# Testing of Ultrafire WF-138 and WF-139 chargers



## GrAndAG (Oct 14, 2008)

Recently I've made some tests of my Ultrafire chargers and just wanted to share some results...

*UltraFire WF-138*



 

*Test results (Li-Ion 3.6V)*





- averaged by 10 sec


 - without averaging _(click to enlarge)_

The charging was started at 260mA current, which decreased slightly and almost constantly during the process to 180mA at the end. The charging voltage was 4.35V at the end of charging. When the charging was finished there was no charging current (0mA, no tickle charging), the battery voltage was 4.26V (after 0.5 sec), after 30 min - 4.20V. 
It seems the charger uses CC method only, but the its power supplier is a bit weak to provide proper power.


*Test results (LiFePO4 3.0V)*




- averaged by 10 sec


 - without averaging _(click to enlarge)_

The charging was made by 320mA current during almost whole process, and only at the last 3 minutes there was a slight decrease to 250mA with rapid increase in voltage (to 4.0V) simultaneously. Battery voltage was 3.80V just after the charging, and decreased to 3.40V after 3 minutes.



*UltraFire WF-139*



 
*Note:* I have the new generation charger, the 5V open circuit.

*Test results:*




- averaged by 10 sec


 - without averaging _(click to enlarge)_


- zoom on transition phase _(click to enlarge)_

The specs clam that the charging current is 450mA, but the actual charging was made at 360mA. When 4.15V was reached the current started decrease slightly, which should be supposed to be the CV stage. But the weird things happened here - the charging current dropped to 220mA, continued decreasing during following 70 seconds to 170mA, after that the charging almost stopped. After 10 seconds the charger "woke up" and increased the current back. the rest time it tried to work in CV mode, but without a huge success. The maximum charging voltage was 4.25V (260mA) at the end, after that the charging stopped. When the charging was finished there was no charging current (0mA, no tickle charging), the battery voltage was 4.16V (after 0.5 sec), after 10 min - 4.14V.

*Addendum:* After an hour I decided to continue charging of that battery by switching off/on the charger. The charging recommenced. The charger easily exceeded the previous stop limit and continued to feed the battery. During the next hour it additional added 250mAh to the battery. Why did it stop the charging earlier before? I have no idea.
*But!* After that hour, when the charging voltage was 4.35V (@200mA), the interesting thing happened - the voltage started jumping from 4.35V to 4.9V and back! I suppose it was the result of battery protection PCB work. But the charger ignored that event and continued to charge. After 25 minutes I decided to abort the experiment, because it seemed the charger wont stop. The battery voltage showed 4.28V after the experiment and did not decrease after 10 minutes.
The charts:



 - "overcharging" _(click to enlarge)_


 - magnified _(click to enlarge)_


*P.S*. Sorry for my ugly English.


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## EngrPaul (Oct 14, 2008)

Thank you!

What battery are you charging?


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## GrAndAG (Oct 14, 2008)

WF-138 was tested with:


- DX's BTY CR123A 3.7V 850mAh
and


- DX's Lithium LiFePO4 Battery (350mAh)

WF-139 - with:


- DX's Ultrafire 3.7V 2400mAh LC 18650 Protected Battery


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## rantanplan (Oct 14, 2008)

I monitored the charging voltage of my WF-139 some time ago and the charging voltage reached levels of above 4.30V too ... even though the battery measured only 4.18V after correct charge termination, I don´t use my WF-139 anymore.

The RC guys with their LiPos are saying that even some milliseconds above certain critical voltage levels do harm their batteries ... so for myself I assume that LiIons with cobalt chemistry don´t like such high voltages neither. There are cheaper chargers that do that job better than the Ultrafire crap ... 

In the meantime I got a RC charger which can charge everything pretty nice, so my WF-139 is already half in the garbage can  ...


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## SilverFox (Oct 14, 2008)

Hello GrAndAG,

It is generally thought that any time spent over 4.20 volts will reduce the cycle life and capacity of a Li-Ion cell. This charger seems to spend a lot of time with the cell over 4.20 volts...

Many cell manufacturers recommend charging at 0.7C. It seems that at this rate the time spent a 4.20 volts is somewhat minimized.

The RC people have tried charging at faster and slower rates and they have settled on 1C. This is a little faster than the 0.7C recommendation, but it seems to work well.

I don't know how much this over voltage effects the cells. Does anyone have any information on cycle life with cells charged on this charger?

Tom


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## konut (Oct 17, 2008)

rantanplan said:


> There are cheaper chargers that do that job better than the Ultrafire crap ...
> 
> In the meantime I got a RC charger which can charge everything pretty nice, so my WF-139 is already half in the garbage can  ...


 
And which charger would that be?


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## jirik_cz (Oct 17, 2008)

I have Digital Li-Ion 18650 Battery Charger from DX. It has 4.18V open circuit voltage. Light goes green at 4.15V then trickle charges to 4.18V and stays there. But my friend has this charger too and it overcharges to 4.27V  Has anyone experience with solarforce chargers?


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## cheetokhan (Oct 17, 2008)

GrAndAG, what equipment did you use to measure the voltage and current and to generate these graphs?


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## GrAndAG (Oct 17, 2008)

I used Medusa Power Analyzer Pro.


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## mdocod (Oct 17, 2008)

GrAndAg,

You're english is great IMO! Don't worry about that! The Tests are Awesome!

I am really glad to see these tests and I can not tell you how much I appreciate it. I am always looking for more good information about chargers and batteries. 

So we know that these chargers are not following the recommended charging algorithm as per manufactures recommendations for li-ion cells. Very few actually do. Oh well....

I've found myself using my old DSD more and more lately after I did a crude test of my 139 and found it pushing cells over 4.30V during charging. The DSD will bring cells up around ~4.25V at the highest during the charge, and always terminates without trickle and cells always settle quickly after termination to less than 4.20V.


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## rantanplan (Oct 19, 2008)

konut said:


> And which charger would that be?



The "Digital Li-Ion 18650 Battery Charger" (sku.6105) from Dealextreme is working fine. It is using the CC/CV method and charges the batteries close to 4.2V. no serious overcharging ... and that for less than $9 shipped .

I´m using now a GT Power A6-10 (=chinese copy of e-station BC-6 from Bantam, $80 w/o shipping from HK). The A6-10 can charge 1-6 cells (LiIon/LiPo) with up to 10A and NiMH, NiCD and PB of course too. There are lots of similar chinese charger (iMAX, Mystery,...) ... they are much cheaper than original ones, therefore the quality you get is a "lottery" too. I had luck with my charger so far, others didn´t with this "cheap way". I chose this one because of the PC interface ... if you don´t need that, the "Tenergy Microcontrolled ...." charger (1-4 cells), available at all-battery.com, should be a nice one too.

My A6-10 tends to undervolting by 20mV, so a single LiIon comes out with 4.18V max ... fine for me-

But I would still use my cheap charger from DX for my 18650s, but I fried one channel during testing. I remembered that I´d done some tests with my chargers a couple of month back, I even found the graphs :

 ... my WF-139 did over 4.4 volts, now I remember. 

Ultrafire WF-139




bigger one

Digital Li-Ion 18650 Battery Charger




bigger one

In both tests I used two discharged Trustfire 2.500mAh. Voltages of both channels were monitored by a Labjack U12 DAQ device. The measurement wasn´t the most precise one which you can see at some spikes due to movement I guess, but it should good enough. The behaviour of the WF-139 was interesting. Every couple of seconds it stops charging and the battery drops to resting voltage. You only have to look at the lowest values of a small period of time and get the real battery voltage. You can see clearly see too that the WF-139 use only a CC charge ... that´s why the voltage gets so high.


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## 12Johnny (Mar 31, 2009)

Thanks for the superb test!


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## moldyoldy (Apr 1, 2009)

rantanplan said:


> The "Digital Li-Ion 18650 Battery Charger" (sku.6105) from Dealextreme is working fine. It is using the CC/CV method and charges the batteries close to 4.2V. no serious overcharging ... and that for less than $9 shipped .
> 
> I´m using now a GT Power A6-10 (=chinese copy of e-station BC-6 from Bantam, $80 w/o shipping from HK). The A6-10 can charge 1-6 cells (LiIon/LiPo) with up to 10A and NiMH, NiCD and PB of course too. There are lots of similar chinese charger (iMAX, Mystery,...) ... they are much cheaper than original ones, therefore the quality you get is a "lottery" too. I had luck with my charger so far, others didn´t with this "cheap way". I chose this one because of the PC interface ... if you don´t need that, the "Tenergy Microcontrolled ...." charger (1-4 cells), available at all-battery.com, should be a nice one too.
> 
> ...



With an oscilloscope this was a good test. A DMM simply cannot react fast enough to register the resting voltage which evidently is the basis for cutoff of charging. 

FWIW, My observations also support the theory that the WF-139 uses a CC charge. the best example of that is to observe the voltages when charging an 18650 cell and when charging an RCR123 cell, both AW branded. The 18650 cell overshoots the intended 4.2v cutoff by very little because of the much lower internal resistance. Charging the RCR123 cell results in voltage much higher than 4.2v because of the comparatively much higher internal resistance. 

Note that some battery charger designs do not like to have the power cycled in the middle of charging - that messes up their programming. First the mains power, then insert the battery. If you want to restart charging, always remove the battery, then reinsert some seconds later.

I wonder about the presumed cell damage under conditions of a constant current charge cycle raising the cell voltage above the desired 4.2v when in fact the cell chemistry is still below a nominal fully charged state. Is the cell damage incurred by overcharging the chemistry beyond a full charge? Or does is the cell damage incurred at any time when the cell is above 4.2volts regardless of the status of the cell chemistry?? When does the proposed cell damage occur?


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## moldyoldy (Apr 1, 2009)

GrAndAG said:


> <snip>
> *P.S*. Sorry for my ugly English.


u vas otlichnij anglijskij yasik. Pyatyorka! :wave:


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## DHart (Apr 2, 2009)

139 user listening closely...


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## mdocod (Apr 2, 2009)

moldyoldy said:


> With an oscilloscope this was a good test. A DMM simply cannot react fast enough to register the resting voltage which evidently is the basis for cutoff of charging.
> 
> FWIW, My observations also support the theory that the WF-139 uses a CC charge. the best example of that is to observe the voltages when charging an 18650 cell and when charging an RCR123 cell, both AW branded. The 18650 cell overshoots the intended 4.2v cutoff by very little because of the much lower internal resistance. Charging the RCR123 cell results in voltage much higher than 4.2v because of the comparatively much higher internal resistance.
> 
> ...



:twothumbs

I really like the way you explained the "CC" only charge methods and proofing that based on the different effects on different cells sizes (I've come to the same conclusions but I really appreciate your method of explaining it as we need more ways to make this make sense to the masses!)...

As for when and how much cell "wear-and-tear" occurs during CC-only charging... this is something I have wondered quite a bit myself. After a great deal of pondering on this one, I have come to the conclusion that cell manufactures would have noted a CC-only charge method in their "specs" if it were equally viable as the CC/CV and could generate equally good cell health and life. Problem is, I haven't seen a single spec sheet even mentioning this charging routine, which leads me to believe that it is probably not the best thing for the cells. 

Imagine filling a tank or bottle with a fluid. when you force fluid in a stream into the container, a "bubbly" surface of the fluid develops. If you want to fill the container to the top without spilling anything, you have to slow down the fill rate towards the end so the bubbles can settle. I think of filling a Li-Ion cell very much like this, if you want to "fill it up" properly, without any wasted cycle life, (spilled fill material), you have to slow down the charge rate at the end of the charge.


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## moldyoldy (Apr 3, 2009)

Hmm, here is a rather hard-nosed view of Li-Ion chargers from an engineering design standpoint: 

A product is designed to a set of requirements. That product is later released for sale with identified specifications. Any use outside of those identified specifications not recommended. Any deficiencies in design as derived from usage reports is then incorporated into a revised set of requirements. The design cycle begins anew.

It needs to be noted that the sales and specification information posted on the average reseller's website is up to the reseller as to how accurately the information reflects the original specifications for the product. Even more pointedly, a nominal perusal of the specifications from the manufacturers website (or as close as I am able to find) for some sample Li-Ion battery chargers indicates an inconsistency between the identified specifications and the information posted on reseller's websites or the reported casual use of Li-Ion chargers by flashaholics. 

Using the charger specifications for the WF-139 charger as an example: Battery to be charged: "18650, 17670, 18500, 14500, 17650, 17500". Battery type identified is "Li-Ion". That is all. The WF-139 charger specifications do not identify an RCR123a or an IMR 16340 cell. Just because the charger output is for 3.7v @ 450ma and cuts off at 4.20v does NOT mean that the charger is automatically applicable to any Li-Ion cell of the 3.7v output type. The WF-139 is commonly sold with spacers to charge lower capacity cells such as the IMR16340 or RCR123 cell in a charger slot intended for a maximum of the 18650 size. This usage practice is NOT per specification of the charger. 

In the case of the WF-139 Li-Ion charger, a high capacity cell such as an 18650, which was identified in the charger specifications, evidently does stay w/in acceptable charging tolerances. A low capacity cell such as the RCR123a, which was NOT identified in the charger specifications, often demonstrates an overvoltage while under charge (exceeding 4.2x volts). Since the constant current charging method briefly stops charging to measure the cell voltage, a digital voltmeter is not an acceptable measurement device for the cell while the cell is being actively charged. Caveat: The number of test samples is relatively low - 5 of the RCR123a and 4 of the 18650 types. 

Silverfox and many others have already amply warned the CPF community of inherent difficulties with lower capacity cells charged in a higher capacity charger, even the PILA charger! On the other hand, you "get what you pay for". A cheap charger with loose tolerances, even if designed for the RCR123a Li-Ion cell, can be just as "bad" as the WF-139 which was not designed for the RCR123a Li-Ion cell. 

However, from a practical usage standpoint, I have been unable to determine a usage life difference between chargers that over-voltage the cells vs chargers that never allow a charging voltage to exceed 4.2 volts. So far in my limited experience, the variability between cell brands is more the determining factor of lifetime than the charging method as used by the Nano, WF-139, WF-138, Pila, SoShine, including the use of spacers in charger slots for cells of the 14500 size or above. My lack of experience with only maybe a 100 Li-Ion cells of various brands will automatically defer to the experts such as Silverfox, et.al.

Back to the design engineering aspect of CC vs CC/CV vs whatever charging method for Li-Ion cells. I am so far unable to find design information for a Li-Ion cell which addresses my own question regarding over-voltage applied to the cell terminals vs charge state in the cell. 

I was able to find ample information on many ICs designed for single and multiple cell charging of Li-Ion cells/batteries as well as reputable information sources such as the "batteryuniversity.com" website. English or German language websites for IC specification information were accessed. These websites were all quite consistent in identifying a common charging method for Li-Ion cells, namely the CC/CV method. The primary control is focused on the cell terminal voltage (3.7v types). An initial condition with a lowered cell voltage results in a low-rate current controlled charge. Once the cell voltage reaches an acceptable voltage level, a full-rate current controlled charge is initiated. However some ICs simply release the full constant current rate into the cell until the cell voltage reaches the target voltage. When the cell voltage at the terminals rises to 4.1 or 4.2 volts, the charge method is transitions to a constant voltage charge method. With a constant voltage applied, the charge current is free to ramp down. Once a certain low-current level is achieved, charging is stopped. No trickle-charging. 

CC vs CC/CV chargers? CC is cheaper to implement than a CC/CV which requires two control methods.

Another design comment. The open terminal voltage on low-cost chargers is only an indication of the design methods used in the charger. It has no real relevance on the charge delivered to the cell. Any electronic control circuitry requires some "overhead" of voltage with which to regulate the voltage to a lower level. Lowest cost power supply design will not regulate or poorly regulate the output voltage with no load. ditto for chargers. Once the charging is stopped, the voltage rises to the uncontrolled level. The change in design of the WF-139 from 11.x volts open circuit to 5.x volts open circuit is just that - a change in design. Evidently that change was to accomodate the revised design requirement to NOT trickle-charge a Li-Ion cell.

Having said all this, I recommend that this thread be converted into the other much longer thread running on the WF-139 charger and this thread be closed. No point in having 2 threads to track!

Sorry for the length of post!


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## foxtrot29 (Apr 3, 2009)

Odd, it seems the wf-139 is inconsistent from user to user. 

Mine seems to terminate at 4.15, consistently (RCR123), then the cells seem to drop to about 4.14.... This is sufficient for me, however I'd like if it took them to at least 4.18. I can get them up that high by taking them out and putting them back.


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## moldyoldy (Apr 3, 2009)

foxtrot29 said:


> Odd, it seems the wf-139 is inconsistent from user to user.
> 
> Mine seems to terminate at 4.15, consistently (RCR123), then the cells seem to drop to about 4.14.... This is sufficient for me, however I'd like if it took them to at least 4.18. I can get them up that high by taking them out and putting them back.



Understood that your sample may be "ok". However if you review the graphs w/o averaging presented in post #1 and click on them to obtain the larger image, depending on the cell type under test, the peak voltage may well be above a desired limit. A digital voltmeter will only see the averaging, not the peak voltages. Most of us do not have an oscilloscope or equivalent recording device to record the highs and lows of the pulsed voltage across the terminals of a cell under charge. That is why it is so difficult to compare answers for different chargers.


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## foxtrot29 (Apr 3, 2009)

moldyoldy said:


> Understood that your sample may be "ok". However if you review the graphs w/o averaging presented in post #1 and click on them to obtain the larger image, depending on the cell type under test, the peak voltage may well be above a desired limit. A digital voltmeter will only see the averaging, not the peak voltages. Most of us do not have an oscilloscope or equivalent recording device to record the highs and lows of the pulsed voltage across the terminals of a cell under charge. That is why it is so difficult to compare answers for different chargers.



It's too complicated, most people won't even check the voltage out of the meter. I can't be expected to do much more! lol

I'll just hope this is good, continue with my inferior testing, use my ZTS, and be happy. If I get shortened life out of my cells, so be it -- I'll buy more!


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## moldyoldy (Apr 3, 2009)

foxtrot29 said:


> It's too complicated, most people won't even check the voltage out of the meter. I can't be expected to do much more! lol
> 
> I'll just hope this is good, continue with my inferior testing, use my ZTS, and be happy. If I get shortened life out of my cells, so be it -- I'll buy more!



I certainly understand your frustration. In any case, I am impressed you that you even took the time to check the cell voltage at full-charge on or off the charger. That alone demonstrates that you are paying attention! Lithium-something cells are still developing and we all have to learn and adapt as the technology changes! My complements!


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## Black Rose (Apr 11, 2009)

Against my better judgement I decided to put my new 1600 mAh AW 17670 Li-Ion in the "good" charge bay of the new WF-139 unit I received that I consider to be faulty.

The battery was used to about 3.86 volts and then put on the charger. 
The charge just terminated and the cell is showing an open circuit voltage of 4.18 volts. The charge took about an hour and a half.

EDIT: I just topped off a new AW 16340 that was at 3.99 volts (using AWs spacer). The charge terminated and the cell is reading 4.12 volts.

:thinking:


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## DHart (Apr 11, 2009)

My WF-139 was purchased in January/February 2009 and open voltage readings fresh off the charger are typically around 4.16 to 4.17. Open voltage of each bay without cells in place is 4.94v. The charger has, as far as I can tell, been serving me and my Li-Ions very well. But I really don't know if the charger is ruining my cells of not. Could be. Or not. I will await info from those more proficient in these matters than myself.


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## mdocod (Apr 11, 2009)

There still seems to be this continued misconception that because cells come off the wf-139 at an acceptable voltage, that the charging method is therefor automatically "OK." I made a video in another thread awhile back, and have been saying for some time now, that it's not the resting voltage after termination I am terribly concerned about here with the WF-139, it's the charging voltage. 


Again, the reason RCR123s consistently terminate at ~4.15V +/-0.01V for most people on the WF-139 is because the 4.35V limit on the PCB is tripped during charging, which isn't considered by me to be an ideal charging practice otherwise the cell manufactures might include mention of said charging practice in their cell information and safety PDFs. Every li-ion cell manufacture calls for a CC/CV charge method, however, most do mention a maximum safe voltage as 4.20V+/-0.05V, or 4.25V absolute maximum, so if a charger is designed such that it uses a CC only charge, provided the charge rate is such that the charge voltage never exceeds 4.25V, then the manufactures recommendations have not really been breached.

Molyoldy, excellent thoughts there, I too have reservations about whether the charge voltage being over the maximum rated cell voltage is a big or small deal... tough call. Until I can confirm otherwise, I'll recommend against this charging routine. 

I'm thinking, maybe the best way to test for the effects on cells would be a long term test involving hundreds of cycles. 2 cells of the same size/brand/age, both start a life being charged and discharged every day for a few months, get a hundred or so cycles on them. Log the capacity of the cell through each discharge, but with one cell always charged on a WF-139, and the other on something known to have a CC/CV charge, or at least a lower voltage cutoff of some sort. If the WF-139 is truly harder on cells as I suspect, then it should be possible to test the hypothesis 

-Eric


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## Outdoors Fanatic (Apr 11, 2009)

I think I'm gonna stick with Laptop chargers from ACER or Toshiba.


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## DHart (Apr 12, 2009)

mdocod... I've edited my last post. Saying that I've been happy with how my WF-139 has performed doesn't mean I'm endorsing the choice as a very good one or encouraging anyone else to do so. Perhaps I'm ruining my cells with every charge.... I really don't know! :thinking: I'm far behind the eight ball as compared to mdocod... so I'm going to continue using my WF-139 *for now* and also stay tuned in to what those more knowledgeable than I (meaning Silverfox, mdocod, and others!) determine as a better way to go. If my Li-Ions die an early death, so be it... I'll have to buy some more!

Thanks to you guys for your diligent evaluations, analysis, and recommendations! :twothumbs


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## Black Rose (Apr 12, 2009)

I really don't know what to make of this based on all the other info that's been posted about the WF-139.

While I was cleaning some mason jars in the kitchen I had the WF-139 charging an unprotected 18650 on the stove. I kept an even closer watch on it since the cell had no protection circuit.

It terminated within a glance at the charger, I immediately took the cell out and tested it with my DMM. It was exactly 4.20 volts.


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## Turbo Guy (Apr 18, 2009)

Ball park volts versus capacity .

4.1 per cell is 90%
4.2 is 100%

10% difference.

This last 10% adds a lot of time to the charge (CV stage) and reduces the life by 200 to 400% depending on who's data you chose to believe.
IMO charging to 4.2 per cell is a waste of time and battery life. A 2000 mAh cell charged to 90% still has 1800 mAh (well it would if it was realy a 2000 to begin with.)

A flashlight that has a 60 min. runtime on hi with a fully charged cell would have 54 min. on one charged to 90%. Like I have advised RC ers for years, if you really need 2000 then use 2200 cells and settle for 4.1 (90%) charges. 

FYI In years past Li ion cells were listed 3.6 nonimal and were charged to 4.1 per cell. I have seen no proof that the newer cells which are now listed as 3.7 nonimal and charge to 4.2 are really any different but then I am only a users not an insider.

Test subject, Tenergy 2600 Li ion which was charged approx. 2 wks. ago. to 4.2V. Today open volts 4.16. Placed in flashlight with 800 mAh drain for 15 min. . When removed 4.02 and after 10 min. 4.05.
Placed on charge and added 170 mAh ,removed waited 10 min. 4.14 volts.


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## moldyoldy (Apr 18, 2009)

FWIW, not to distract from the topic title, but I just received 5 Nano chargers - RCR123 - from Lighthound and have been running them thru their paces with AW RCR123a cells. Caveat noted that all I have left for test gear is a good DMM. no O-Scope. All Nano chargers were properly functional. The LEDs turned green from 4.13-4.17 volts. Once the LED turned visibly green, there was still a bit of trickle charging. That could be attributed to simply not being able to see the remaining yellow color. The LED changes from red to yellowish fading to green. In any case, leaving the cells in the chargers overnight resulted in the voltages drifting up a bit. The lowest was 4.15 and the highest was 4.20v. There was no further change in voltages even with leaving the cells in the charger for over a day - not recommended. Quite acceptable voltage numbers. 

Why do I bother with a Nano charger? It is small and very portable. It also is light enough to use on the end of an adapter for the usual middle Euoprean mains plug at 240VAC. The weight of the cell plus charger is not too heavy for plugging directly into the mains socket.


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## 325addict (Apr 20, 2009)

Well, just one of the reasons for designing my own Li-ion charger is the fact, that even "good-on-paper" chargers sometimes seem to overcharge.

I just yesterday finished my design. A PCB for it has been designed now.

Brief design stats:

1. voltage EXACTLY 4.2000V
2. using proper CC/CV-method, *switch off-current of 3% of capacity*
3. LEDs tell: CC or CV-charging, so you know in what stage the process is,
4. won't charge batteries with less than 2.5V residual charge,
5. capacity switchable: 0,5Ah, 1Ah, 2Ah
6. safety-catch when, for WHATEVER reason, voltage comes over 4.25V

This involved lots of electronics.... 34 resistors, 4 ICs, three transistors, 2 power MOSFETs, 8 capacitors, three 25-turn trimmers for ultimate accuracy, and lots of diodes (lost count).
No microcontroller.... I don't understand those things, I can't do anything with them. I am an analog designer....

It is on a PCB of 100X65mm CRAMMED FULL of parts. And... it must be made multiple times, as it has been designed for the charging of just ONE cell 

Now the production of a prototype is the next step...


Timmo.


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## jzmtl (Apr 20, 2009)

So are there any decently priced charger for 18650 that use cc/cv method?

Yes I know about Pila, it's very expensive for people outside u.s. to get one.


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## csshih (Apr 20, 2009)

now timmo.. that sounds like something to look forward to!


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## Black Rose (Apr 20, 2009)

jzmtl said:


> So are there any decently priced charger for 18650 that use cc/cv method?


There is one on the CPF page at Battery Station. 

They are being sold for $9.00 (CPF) + shipping. It's a Yoho-122

CC/CV, peak current: 1A per channel (2A total) 
4.2v termination (+/- .1v) 

BullzeyeBill has been using one for quite some time for protected and unprotected cells and has had no issues at all with it.


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## rantanplan (Apr 20, 2009)

jzmtl said:


> So are there any decently priced charger for 18650 that use cc/cv method? [...]





rantanplan said:


> The "Digital Li-Ion 18650 Battery Charger" (sku.6105) from Dealextreme is working fine. It is using the CC/CV method and charges the batteries close to 4.2V. no serious overcharging ... and that for less than $9 shipped .







Black Rose said:


> There is one on the CPF page at Battery Station.
> 
> They are being sold for $9.00 (CPF) + shipping. It's a Yoho-122
> 
> ...



Same Experience here ... the Yoho-122 is a good one (if its still using the same circuit )


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## DHart (Apr 20, 2009)

The Yoho 122 sounds like a great buy with the desired charging method... what's the downside to it, if any?

What charging method does the WF-139 use?


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## Black Rose (Apr 20, 2009)

DHart said:


> The Yoho 122 sounds like a great buy with the desired charging method... what's the downside to it, if any?


It can't charge cells that have less than 1000 mAh (i.e. 16340, 14500, etc).



> What charging method does the WF-139 use?


Appears to be CC only (although some sites advertise it as CC/CV) and it looks like it exceeds 4.2v during charging.

I was charging a TrustFire 16340 yesterday and the best I could get was 4.13 volts....the overcharge circuit on the cell kept tripping, thus ending the charge.


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## old4570 (Apr 22, 2009)

Ok There Cheap , 

My WF-138 is just fine .. Never goes over 4.2 
The WF-139 does about 4.22 or 4.23 with unprotected cells 18650 ,of the charger ...
The batts I charged last night are sitting on 4.2 right now - some 14 hours after charging .
Only the UF- BRC3000's are sitting on 4.16 after terminating @ about 4.18 

Protected cells run 4.17 or 4.18 

CR123's go about 4.17


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## rantanplan (Apr 23, 2009)

old4570 said:


> Ok There Cheap ,
> 
> My WF-138 is just fine .. Never goes over 4.2
> The WF-139 does about 4.22 or 4.23 with unprotected cells 18650 ,of the charger ...[...]



Have you monitored the voltages during the charging process? Guess not ...

Overcharging (=batteries come out with too much volts) isn´t the problem of the Ultrafires, at least not of the newer ones. Problem is, that they apply high voltages far beyond 4.2V to the batteries while charging.

AFAIK there are no scientific tests about the negative impact like there are about overcharging etc. But I strongly believe that the "CC-only" style of the Ultrafires DOES harm the batteries. I used a WF139 too and am now looking onto a basket full of unusable LiIons ...


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## old4570 (Apr 24, 2009)

Open Circuit = 4.97 volts 

BAtt Voltage = 4.12 in charger 4.15 

If I put the MM in series it reads under 1v 0.86 with a CR123A 
and 0.68v with a 18650 

Amps with a CR123 go .38 then drop to .28 and back up to .38 

Amps with a 18650 go .35 down to .24 and up again to .35 

Well thats my WF 139 ...


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## wapkil (May 4, 2009)

I have just finished testing my Ultrafire WF-139. I've bought it around a month ago from DX. It is a version that has 4.26V OC voltage when measured without batteries inside and doesn't blink with the LEDs when charging.

I have placed a partially discharged "Blue" TrustFire 900 battery inside the charger, started measuring the voltage and started charging:





I have unplugged the charger when the voltage exceeded 4.25V. It seems that my WF-139 simply pushes current inside the battery, no matter what the voltage is or what its own LED shows. 

I have bought at DX an Akoray K-106 light that used to work, this WF-139 charger and two Trustfire LiIon batteries:duck: I think I will have to reconsider buying from DX anything with electronics inside...


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## GrAndAG (May 4, 2009)

It seems the charger (3rd generation or faked) acts like TrustFire TR-001.



GrAndAG said:


> I tested TrustFire TR-001 charger. Here is the graph of charging process:
> 
> 
> 
> ...


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## wapkil (May 4, 2009)

GrAndAG said:


> It seems the charger (3rd generation or faked) acts like TrustFire TR-001.



Thanks for the link. Yes, it seems that I have a 3rd revision of this charger. It behaves the same way the TR-001 does and has a license number on the back label. So there is also the charger lottery and I've lost. Oh well, you get what you pay for.


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## Black Rose (May 4, 2009)

wapkil said:


> Thanks for the link. Yes, it seems that I have a 3rd revision of this charger. It behaves the same way the TR-001 does and has a license number on the back label. So there is also the charger lottery and I've lost. Oh well, you get what you pay for.


I have a 2nd revision WF-139 that has the license number on the back label.

Here is GrAndAG's list on how to determine which revision of the WF-139 you have:
https://www.candlepowerforums.com/posts/2940000&postcount=13


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## wapkil (May 5, 2009)

Black Rose said:


> I have a 2nd revision WF-139 that has the license number on the back label.
> 
> Here is GrAndAG's list on how to determine which revision of the WF-139 you have: https://www.candlepowerforums.com/posts/2940000&postcount=13



Yup, I've read this thread - my WF-139 is 4.26V OC and has all the other characteristics of the 3rd revision. Unless of course they came up with some another similar version in the meantime.

I was surprised that with all the single-chip LiIon charger circuits it is still possible to create something that doesn't charge correctly. It was probably a few cents cheaper this way...

Today I received a single cell universal charger for LiIons and NiMHs (sku 14885)- will see how this one behaves. Hopefully this time they used a dedicated circuit and not another in-house "invention".


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## old4570 (May 6, 2009)

I was looking at this one , 1.2v 3.6v and 9v charger . :candle: sku 14885
Let us know how it goes :


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## wapkil (May 6, 2009)

old4570 said:


> I was looking at this one , 1.2v 3.6v and 9v charger . :candle: sku 14885
> Let us know how it goes :



I will post the summary when I'm finished testing it. I now have data from a 14500 charging and this one seems to undercharge. This test was conducted with an additional cheap, old (and with a history of abuse) DMM to measure the current and I don't know if it didn't interfere with the charging process. I'm currently testing the charger with an AA NiMH and I will repeat the LiIon test later.

I'm only not sure where should I post the results. Should I resurrect this thread, post in your thread (I test AA/14500, not 17340/18650 as in the title), add the information here, start a new thread... ? :shrug:


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## wapkil (May 8, 2009)

wapkil said:


> I will post the summary when I'm finished testing it. I now have data from a 14500 charging and this one seems to undercharge. This test was conducted with an additional cheap, old (and with a history of abuse) DMM to measure the current and I don't know if it didn't interfere with the charging process.



I have finally found some time to look at the test results. It seems that the second DMM indeed interfered with the charger algorithm so please disregard the plot from the link above. I posted the description of my test results in this thread.


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## recDNA (Jul 14, 2009)

I just want to make sure I understand this thread correctly.

I want a charger for protected AW18650 batteries

4-7s sells the AW's Dual Bay Fast Charger AW-139 [AW.chg139] and I have always trusted their products.

You are saying it is not a good charger right?


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## mdocod (Jul 15, 2009)

recDNA,

dual posting is not allowed... I just answered *basically* this same question over in this thread...

-Eric


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## recDNA (Jul 15, 2009)

mdocod said:


> recDNA,
> 
> dual posting is not allowed... I just answered *basically* this same question over in this thread...
> 
> -Eric


 
I didn't start this thread Eric. I searched and found an applicable thread. I asked the same question in MY thread specifically because you had been so helpful. My title had nothing to do with chargers so my expectation of a reply was low.


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## Outdoors Fanatic (Jul 16, 2009)

recDNA said:


> I just want to make sure I understand this thread correctly.
> 
> I want a charger for protected AW18650 batteries
> 
> ...


Just because a seller is respected it don't automatically mean that all his products are 100% perfect or reliable. AW also sells the WF-139.

And to asnwer your question: No, this charger is definitely not good, many would even say it is a total piece of crap. Get a Pila IBC if you want a decent charger.


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## DHart (Jul 16, 2009)

Outdoors Fanatic said:


> And to asnwer your question: No, this charger is definitely not good, many would even say it is a total piece of crap. Get a Pila IBC if you want a decent charger.



While the Pila is undoubtedly a better charger, a recent model WF-139 are not a "total piece of crap". Many members here are happily charging li-ions with Pilas and WF-139s. I have used my WF-139 to charge a great many 16340, 14500, 17500, 17670, 18500, and 18650 cells - many times over. And every time they come off the charger at or just below 4.2. That doesn't mean they are being charged in the most "ideal" manner possible, or with the best algorithms, but they are certainly adequately charged and not over charged for a reasonable price. 

Regardless of the charger you use, it's important to understand that charging lithium ion cells involves some risk and must be done with a certain degree of care and understanding. Be present while charging and pull your cells off the charger when the done light goes on. Don't put li-ions on any charger and leave the house for an indefinite period of time... that is risky. Also smart to put your charger on a fireproof base, such as a stone tile or two.

For the money (about $19) the WF-139 is an adequate charger. If you don't mind spending more money, at around $40? the Pila is a good choice with an arguably better charging algorithm. With either one, use a good multimeter to check charged voltages to make sure things are at or below about 4.2.


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## recDNA (Jul 16, 2009)

DHart said:


> While the Pila is undoubtedly a better charger, a recent model WF-139 are not a "total piece of crap". I have used mine to charge a great many 16340, 14500, 17500, 17670, 18500, and 18650 cells - many times over. And every time they come off the charger at or just below 4.2. That doesn't mean they are being charged in the most "ideal" manner possible, but they are certainly adequately charged and not over charged.
> 
> Regardless of the charger you use, it's important to understand that charging lithium ion cells involves some risk and must be done with a certain degree of care and understanding. Be present while charging and pull your cells off the charger when the done light goes on. Don't put li-ions on any charger and leave the house for an indefinite period of time... that is risky. Also smart to put your charger on a fireproof base, such as a stone tile or two.
> 
> For the money (about $19) the WF-139 is an adequate charger. If you don't mind spending more money, at around $40? the Pila is a good choice with an arguably better charging algorithm. With either one, use a good multimeter to check charged voltages to make sure things are at or below about 4.2.


 

Even protected 18650's will burst into flame if left on the charger?

Can I safely leave the house with protected 18650's on a Pila?


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## DHart (Jul 16, 2009)

recDNA said:


> Even protected 18650's will burst into flame if left on the charger?



Not in my experience. And I wouldn't think so. But to be safe, I only use protected li-ions (except for 10440s) and I follow the recommended guidelines for use and charging to a "T".

I've never had any charging problems of any kind. But I don't push the envelope by leaving cells on the charger for indefinite periods of time. Even if you did, the chances are that they won't melt down... but I've read enough threads and seen enough photos of charging issues with li-ions that I don't take the chance. I charge my cells when I'm going to be home and keep an eye on the charger from time to time and pull the cells as soon as I get the green light. Never a problem with hundreds of charges. I do believe strongly that anyone who will be using li-ions needs to read a lot of the threads about safety practices that should be observed when using and charging li-ions... and be consciencious about following guidelines.


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## Black Rose (Jul 16, 2009)

When you are charging Li-Ion cells with any charger (Pila, Ultrafire, very expensive hobby chargers) do not leave them unattended for extended periods of time. 

If a cell suffers thermal runaway, you need to react quickly.


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## recDNA (Jul 16, 2009)

DHart said:


> Not in my experience. And I wouldn't think so. But to be safe, I only use protected li-ions (except for 10440s) and I follow the recommended guidelines for use and charging to a "T".
> 
> I've never had any charging problems of any kind. But I don't push the envelope by leaving cells on the charger for indefinite periods of time. Even if you did, the chances are that they won't melt down... but I've read enough threads and seen enough photos of charging issues with li-ions that I don't take the chance. I charge my cells when I'm going to be home and keep an eye on the charger from time to time and pull the cells as soon as I get the green light. Never a problem with hundreds of charges. I do believe strongly that anyone who will be using li-ions needs to read a lot of the threads about safety practices that should be observed when using and charging li-ions... and be consciencious about following guidelines.


 
Then frankly, I can't have any kind of rechargeable lithium battery. I thought I was safe with protected 18650's on the recommended charger (Pila). I *KNOW* myself. I will *DEFINITELY* forget the charger at some point and leave the batteries in it beyond the recommended time. It is not a question of *IF* I will forget - only *WHEN*. As Dirty Harry once remarked, "A man has to know his limitations."

The only thing I can think of is trying to approximate how long it takes to do one charge and attaching the charger to an air conditioner timer (higher power rating than normal timer) and setting the timer as a fail-safe when I'm charging batteries.

It AMAZES me that nobody can figure out how to build a charger that totally shuts off when the green light comes on. If a circuit can be designed the recognize the voltage level and turn on a light it should be able to simply shut off power completely.

Should I be afraid to leave the house because the thermostat won't work and the heat will fail to shut itself off before the house is in flames? No, somebody designed a pretty fool-proof method of shutting off the system before it explodes. Why nobody can do that with a battery charger is beyond me. Where are all the electrical engineers?


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## Mjolnir (Jul 16, 2009)

The PILA _does_ shut off when the green light goes on (although some cheaper chargers don't). However, things can fail. Even if there is only a .1% chance that the PILA will overcharge a cell, it could theoretically happen. Of course, your laptop could also explode while you are charging it. I leave cells charging overnight sometimes because I trust the charger, but I probably would not leave the house with it charging. 

Out of all the chargers though, the PILA is probably the safest to have, should you forget you are charging and leave the house.


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## recDNA (Jul 16, 2009)

Mjolnir said:


> The PILA _does_ shut off when the green light goes on (although some cheaper chargers don't). However, things can fail. Even if there is only a .1% chance that the PILA will overcharge a cell, it could theoretically happen. Of course, your laptop could also explode while you are charging it. I leave cells charging overnight sometimes because I trust the charger, but I probably would not leave the house with it charging.
> 
> Out of all the chargers though, the PILA is probably the safest to have, should you forget you are charging and leave the house.


 
The key is KNOWING that probability. One chance in a 100 is probably too great a risk to justify based on my limited need. One chance in 100,000 is low enough not to worry about. I am confident that the risk of my computer exploding is lower than 1/1000 based on the large number of XPS M1530 sold and the small number of reported cases of explosions. Dell once made an unsafe battery...they quickly got it off the market because they want to stay in business. 

I know very little about the companies that make the 18650 Li-Ion batteries or the chargers but they aren't huge American companies like Dell or Energizer or Duracell so I trust them less.

I suspect the odds of a problem are very low but I have no statistical basis for that gut feeling, no comfort level with companies I've never heard of, and concern based on the repeated warnings I've had here.

In the future I'll make sure to only purchase lights that can be effectively used with primaries.

(BTW, is it better to be sleeping IN the house when there is a fire or someplace else entirely?)


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## recDNA (Jul 16, 2009)

What do you think of my timer idea ? (hook charger to a timer set to 8 hours so worst case scenario when I forget is a few hours of overcharging). When I am better able to guage how long a charge takes I can cut the number of hours on the timer to a closer approximation.

IF I buy a charger it WILL be the Pila. I wouldn't skimp when it comes to safety.


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## DHart (Jul 16, 2009)

recDNA said:


> What do you think of my timer idea ? (hook charger to a timer set to 8 hours so worst case scenario when I forget is a few hours of overcharging). When I am better able to guage how long a charge takes I can cut the number of hours on the timer to a closer approximation.
> 
> IF I buy a charger it WILL be the Pila. I wouldn't skimp when it comes to safety.



Whatever the charger you decide on, it wouldn't hurt to use a timer... just an extra measure of security for those who feel it necessary. Electrical circuits, switchers, components, etc. of all kinds, types, and cost can and do fail. Somewhere in there from extreme to extreme, one just decides on a "comfort zone" and goes with it.


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## recDNA (Jul 16, 2009)

DHart said:


> Whatever the charger you decide on, it wouldn't hurt to use a timer... just an extra measure of security for those who feel it necessary. Electrical circuits, switchers, components, etc. of all kinds, types, and cost can and do fail. Somewhere in there from extreme to extreme, one just decides on a "comfort zone" and goes with it.


 
Plus the added advantage of the ac timer sitting around anyway. No summer so far in New England this year so I haven't had any occasion to use the air conditioner. Global warming my ...

Pila it will be with AW 18650's.


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## Mjolnir (Jul 17, 2009)

Well I have had a fair amount of occasions to use my air conditioner...


If you really want to be safe, you could get/make an all metal box (or one made out of some sort of blast shield), and charge the cell in it. That way, if the cell completely explodes, it won't do anything except ruin the charger (and if the charger overcharges the cell, then it deserves to die anyways). I seriously doubt that a lithium ion battery explosion could punch through metal plating that is even a few millimeters thick.


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## DHart (Jul 17, 2009)

An old metal ammo box from an army surplus shop would make a nice charging container.


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## recDNA (Jul 18, 2009)

DHart said:


> An old metal ammo box from an army surplus shop would make a nice charging container.


 
I have a safe but probably not a good idea to keep the charger with live ammo right? LOL


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## 325addict (Jul 18, 2009)

As long as the CC-only charging limits the VOLTAGE to 4.200V there's not so much that can go wrong.
The only drawback may be, that the battery won't be filled to the brim, as the "last part" (the CV part) of the charging simply misses.

My self-designed charger meets following criteria:

charging current switchable: 250mA, 500mA, 1A
CV maximum of 4.200V
full switch-off at 3% of rated capacity 500mAh, 1Ah, 2Ah
failsafe-switchoff if voltage comes above 4.25V for whatever reason
won't start charging if cell-voltage is under 2.5V
LEDs for: CC, CV, ready, "<2.5V", fail

I think this actually IS a safe charger, which should give great cell-life :thumbsup:


Timmo.


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## HKJ (Jul 18, 2009)

Black Rose said:


> When you are charging Li-Ion cells with any charger (Pila, Ultrafire, very expensive hobby chargers) do not leave them unattended for extended periods of time.
> 
> If a cell suffers thermal runaway, you need to react quickly.



You are aware that most laptop uses 18650 batteries and would need the same protocol!

This is a general problem with lots of electronic, how safe do you wish to be? Even a TV on standby might burst into flame, it might only be 1 in a million, but it does happen, it is the same with LiIon batteries, some batteries does burst into flame, sometimes they are in a laptop and sometimes they are in a charger. But as long as you do tread you batteries the right way, the probability is very low.


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## recDNA (Jul 18, 2009)

I don't know if it's OK to ask about a different charger in this thread but every time I start my own thread somebody tells me the answer is already is some other thread so here goes...

Anybody know anything about the HXY digital charger for 18650's? I found only very old (presumably outdated)nposts about it in my search.

Also...I emailed Batterystation.com and Kevin says they've never carried the Yoho brand charger. Where are they available if I elect to go "cheap". With only one flashlight that uses 18650's it's hard to justify spending $50 for a charger if a less expensive yet still safe alternative exists. I doubt I would ever use RCR123's or any of the smaller rechargeables.


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## oren1s (Jul 19, 2009)

Hi all,

After reading.... i feel uncomfortable using my WF-139 charger! I know there are expensive solutions, like "Schulze" charger.

What do you think of using cell phone (nokia) for charging 1 cell?


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## shadowjk (Jul 21, 2009)

Keep in mind that the cellphone "charger" is just a powersupply, the charger is in the phone and batteries must thus be connected to the phone itself.


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## oren1s (Jul 22, 2009)

Shadowjk,

That's what i have intended to do, using the cell phone itself. I have done so in the past with Nimh celles, charging my RC receiver.


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## donjoe (Jul 28, 2009)

Does anyone know if the WF-138 is picky about where on its power connector it gets the Live and where the Neutral wire from the wall outlet?

I just got the damned thing with a UK plug (BS 1363) and I can't use it with my continental-European outlets (Type C/F). I'm thinking of simply replacing the British plug at the end of the cord with a Type F "Schuko" and forgetting all about the Live & Neutral wire positioning...

... but I'd very much like to not blow up my charger when I plug it in like this.


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## GrAndAG (Jul 29, 2009)

donjoe said:


> Does anyone know if the WF-138 is picky about where on its power connector it gets the Live and where the Neutral wire from the wall outlet?



The polarity does not matter. I got mine with US plug (flat pins) and use the charger through flat-to-round adapter without any problem.


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## donjoe (Jul 29, 2009)

OK, thanks.

Now that I think of it, the only problem should be if there's ever a current surge (short-circuit etc.), because the charger's internal fuse is probably connected to the pin where it expects to have the Live wire, so if it blows when you've connected the Neutral to that pin, it will interrupt the total circuit but some parts of it will still be under current from the uninterrupted Live wire.

Anyway, even if it does blow I'm not planning to put my hands on it before unplugging it from the wall, so I should be fine.


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## GrAndAG (Jul 29, 2009)

donjoe said:


> the charger's internal fuse



I'm not sure whether the charger does have such thing. 
BTW. In Russia there no standard which hole in the outlet socket should be Live or Neutral...


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## donjoe (Jul 29, 2009)

GrAndAG said:


> I'm not sure whether the charger does have such thing.


Oh I'm pretty sure it does. 








> BTW. In Russia there no standard which hole in the outlet socket should be Live or Neutral...


Same in Romania, that's why I asked about it. Not only does the wall plug that came with the charger have fixed L and N positions, but also the power connector on the charger itself is asymmetrical, suggesting that the charger also "cares" about where L and N go. But, as I said, it probably only "cares" because of the fuse.


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## GrAndAG (Jul 29, 2009)

This is just a label. For Chinese products it is not a prove.


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## donjoe (Jul 30, 2009)

Now now, you don't need to diss the Chinese indiscriminately like that, after all Fenix are Chinese too and look at the great job they're doing. 

But anyway, I tried to take the thing apart to look inside and settle the question, but taking out that single screw on the back wasn't enough to allow me to separate the two halves of the case without fear of breaking something. :shrug:


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## Norm (Jul 30, 2009)

donjoe;3030755I said:


> tried to take the thing apart to look inside and settle the question, but taking out that single screw on the back wasn't enough to allow me to separate the two halves of the case without fear of breaking something. :shrug:


The other screws are usually hidden under the label.
Norm


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## GrAndAG (Jul 30, 2009)

I'm more lucky with my WF-138... It has differently shaped label, so the both screws are visible. 





So, inside of the box:


 



The black cylinder near power socket looks like glass fuse in the tube. It's connected to the round pin of the socket.


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## donjoe (Jul 30, 2009)

Norm said:


> The other screws are usually hidden under the label.


Yeah, I know, I tried pressing on the label at various points, but I couldn't feel any additional hole underneath. (I'm not sure I'd be able to feel it even it if was there - the label seems pretty thick.)



GrAndAG said:


> The black cylinder near power socket looks like glass fuse in the tube. It's connected to the round pin of the socket.


Unlike some other people, I actually do like to say "I told you so". :nana:


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## palomino77 (Oct 18, 2009)

GrAndAG said:


> This is just a label. For Chinese products it is not a prove.


 
Well even Pila is made in China.  
Have you guys ever thought; that maybe even Chinese brands are being counterfeited by other Chinese lesser qualities manufacturers? Just like they counterfeit everything else, this is a very common practice in China. A lot of the chargers and batteries on DX are not originals. One of the most counterfeited brands in China is Ultrafire. It is impossible to know which ones are the originals and which are counterfeit; they are exactly the same outside. 

Mainland Chinese (where most of these companies are) do not have access to the DX webpage. For some reason it is being blocked where they cannot see it. Makes you think why doesn't it? :thinking:


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## KiwiMark (Oct 25, 2009)

I have 2 hobby chargers and 2 WF-139 chargers. As far as I can figure this is what happens:
The 2 hobby chargers charge at a rate I specify (CC) until the voltage reaches 4.2V, then they taper off the amperage while holding the voltage at 4.2V (CV) until the amperage has tapered off to 1/10th of the original value then they turn off (no trickle).
The WF-139 chargers charge at a constant amperage until the resting voltage of the cells reaches 4.2V. I have confirmed this by using 2 multimeters with one measuring the amps and the other measuring volts. Each time the light turns green the cells can be checked and measure 4.2V.

It occurs to me that the final result is pretty close to the same either way. However during the final stages of the CC/CV charge the voltage does NOT exceed 4.2V, but with the CC charge (WF-139) the voltage while charging may be 4.25-4.30V. I wonder how much harm that does - I realise that Li-ion cells should not be taken over 4.2V, but on the other hand they only exceed that level for a few minutes at the end of each charging stage. The actual charging state will be about the same from a WF-139 charger as a CC/CV charger - I don't believe that the cells are being over charged, they are just being allowed to have a voltage above 4.2V for a few minutes until their resting voltage = 4.2V.

On the charger is written "Ultrafire Rapid Charger For 3.7V Lithium batteries" - is the "Rapid Charger" a hint at CC charging method which would indeed charge a Li-ion cell noticeably faster than the CC/CV method?

So what I really want to know is this: How much damage would their be to a Li-ion cell if its voltage is allowed to exceed 4.2V while charging for a few minutes at the end of every charge? I would presume that if only charging once every couple of months that the amount of time above 4.2V is so little (per year) that the damage would be almost none, but what if you were charging the cells once a week? What about daily charging?


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## TranceAddict (Oct 27, 2009)

GrAndAg, 

it will be really great if you can analyze this https://www.candlepowerforums.com/threads/233932

i find it troublesome to use scope to do datalogging for current flow.


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## donjoe (Oct 27, 2009)

Finished the first WF-138 recharge of my AWs after they lost the initial charge I bought them with. One finished about 10 minutes earlier than the other, I suspect there might have been some difference in actual capacity and/or initial/leftover charge between them.

I took the first one out no more than 5 minutes after the light went green, measured it open-circuit and got about 3.8-3.9 volts (low-precision multimeter here).

I left the second one in for about 45 more minutes after that (watching a TV episode ), so I don't know exactly when it finished, but it probably had a green light for much more than 5 minutes before I took it out. I measured it and again got 3.8-3.9 volts.

Looks to me like I got a really good charger here, no overcharge at all, not even 4V out of fresh cells. That or I'm doing the measurement wrong.  Or the AW is a very good cell that doesn't stray from its nominal voltage at all.


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