# Duracell Power Gauge CEF21 mod for improved charging of AAA cells



## Mr Happy (Jan 16, 2010)

Here is what the CEF21 looks like inside. This is the Duracell Power Gauge charger (Indicator Charger in Europe).

Top view:






Upper left is the mains power supply. Transformer TNY266B brings low voltage power over to the rest of the circuitry. Lower left there are four parallel power supply channels using four coils (two hidden under the metal shield). These supply 5 V DC to the USB power output lower left when they are not being used to charge batteries. The white socket lower center is where the cable from the LED bar graph display plugs in. Lower right would appear to be a test connector.

Bottom view:





Erm...  

This ain't no simple charger.

I've made these pictures as large as forum guidelines allow. I have higher resolution versions I could link to.

The square chip upper right is an ATMEGA. There is some measure of intelligent control going on in this charger.

The four big resistors seem to be connected between the AAA and AA contacts of each channel. If I read the color code correctly, it is orange-black-silver-red making them 0R3, 2% tolerance.

My goal is to modify the charger so that AAA cells get charged with the same 400 mA that AA cells get. As manufactured, the charger uses 175 mA to charge AAA cells and it seems to be unreliable at terminating. I think it would terminate better at 400 mA.

Edit: Please see post #50 below for details of how to make the modification.


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## Mr Happy (Jan 16, 2010)

*Re: Duracell CEF21 disassembled (modifications, anyone?)*

Here are close up views of the connections around the battery contacts.

Lower side:





Upper side:





I'm beginning to think the resistors are just connected in series in the AAA charging circuit as current limiting components. And therefore if I shorted them out with direct links, the AAA cells would get the full charging current?


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## PeAK (Jan 16, 2010)

*Re: Duracell CEF21 disassembled (modifications, anyone?)*

Seems to be either one extra (maybe two) connection beyond the resistor to this AAA node. 

For the charging bank nearest the test connector, a trace runs along the top view to the middle of the board. On the bottom view, the square pad has a smaller round pad that seems to go nowhere.

I would hazard a guess that the current comes from the AA terminal to the AAA terminal through the resistor. Not sure about the value of the resistor as a 175mA would generate very little heat/watts across a 0.3 ohm resistor...???


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## Mr Happy (Jan 16, 2010)

*Re: Duracell CEF21 disassembled (modifications, anyone?)*

I've been puzzled by those round pads that seem to go nowhere too. But if I hold the board up and shine light through it, they really do seem unconnected.

I was looking for the connections to the AA pads. In each case there seems to be a thick current supply trace leading to the AA connector, and one thin (voltage sensing?) trace leading away.

I think there is a similar situation with the AAA connections: a current supply through the resistor from the AA pad and a sensing trace leading away. I'm trying to follow where those traces go.

Maybe the circuit senses the voltage across those resistors? When an AA cell is being charged the AAA pad will be at equal potential and the voltage difference will be zero. When an AAA cell is being charged the charging current will pass through the resistor producing a voltage drop of 175 mA x 0.3 ohms = 52.5 mV. The circuit may throttle the charging current so that the sensed voltage is less than or equal to ~50 mV?

If those are current sense resistors then I can increase the current to the full value by shorting out the resistors.

The tight tolerance value of 2% would add weight to the idea that they are sense resistors.


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## PeAK (Jan 16, 2010)

*Re: Duracell CEF21 disassembled (modifications, anyone?)*



Mr Happy said:


> ....When an AAA cell is being charged the charging current will pass through the resistor producing a voltage drop of 175 mA x 0.3 ohms = 52.5 mV. The circuit may throttle the charging current so that the sensed voltage is less than or equal to ~50 mV?
> 
> If those are current sense resistors then I can increase the current to the full value by shorting out the resistors.
> 
> The tight tolerance value of 2% would add weight to the idea that they are sense resistors.



It might be an idea to monitor the voltage across "the resistor" when charging a AA battery and also when charging an AAA battery to validate some of the above assumptions about the current traversing it.


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## Mr Happy (Jan 16, 2010)

*Re: Duracell CEF21 disassembled (modifications, anyone?)*



PeAK said:


> It might be an idea to monitor the voltage across "the resistor" when charging a AA battery and also when charging an AAA battery to validate some of the above assumptions about the current traversing it.


Good plan.


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## Mr Happy (Jan 16, 2010)

*Re: Duracell CEF21 disassembled (modifications, anyone?)*

My measurements are consistent with the current sense resistor hypothesis.

I placed a voltmeter between the AA and AAA connectors (+ to AA, - to AAA). When I turned on the charger with an AAA cell connected the voltage difference rose rapidly towards ~80 mV and then dropped down to settle around 50 mV, remaining fairly steady at that value with a small up and down cycle imposed.

On doing the same experiment with an AA cell connected the voltage difference remained close to zero, hovering around -2 mV (why negative?).

For my next test I will short the AAA connector to the AA connector and then charge an 800 mAh AAA cell. If my theory is right it will take about 2 hours to charge and will then terminate on cue.


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## Magic Matt (Jan 17, 2010)

*Re: Duracell CEF21 disassembled (modifications, anyone?)*



Mr Happy said:


> I've been puzzled by those round pads that seem to go nowhere too. But if I hold the board up and shine light through it, they really do seem unconnected.



I'm lead to believe it's some sort of anti-reverse-engineering ploy. I have loads of them in my VCR, and when I spoke to an engineer about it I was told it was to make "building circuits that bypass copy protection, or even just copying the design, much harder".

Given there are fake batteries and chargers out there, I can see some sense in it. It would certainly make it easier to prove a design had just been copied if all the dummy tracks were duplicated!


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## PeAK (Jan 17, 2010)

*Re: Duracell CEF21 disassembled (modifications, anyone?)*



Mr Happy said:


> ....there seems to be a thick current supply trace leading to the AA connector, and one thin (voltage sensing?) trace leading away.
> 
> I think there is a similar situation with the AAA connections: a current supply through the resistor from the AA pad and a sensing trace leading away. I'm trying to follow where those traces go.
> 
> Maybe the circuit senses the voltage across those resistors? ...



Nice Sunday morning project...

There is a style of current source derived from a floating reference voltage that is used in LM78xx type voltage regulators. A voltage is impressed across a resistor that attaches across the output and a sense/feedback node to derive a current.

For the above to hold true in the "fuel gauge" charger, this voltage would correspond to about *93mV* and a resistor of about *0.223 ohms* would be needed to derived the 400mA AA charging current. The 0.3 ohm resistor would be needed to be added in series to the 0.233 ohm resistor to make up a 0.533 ohm resistor to derive 175mA. 

For the bottom charging bank (nearest the test connnector), I see a trace going up from the AA pad and another one going up from the AAA pad that I think you refer to as the "sense" traces. For these to serve this function, they would have to be traced back to the same point on the IC chip. On the bottom view, they seem to do converge toward the middle of the board but then the resolution does not hold up. A high res shot would be useful here.

* Question: *On the top side around the coils glued on the top side are two components marked Z3 and Z4 on the board. This would indicate that they are zener diodes but could they be those 0.223 ohm resistors I mention. A picture would be useful.

* Experiment:* You mentioned that putting a short across the resistor might be one way to boost the current. A half step would be to put a 1 ohm in parallel (held in place by your hand) with the 0.3 ohm resistor and measure the corresponding current going into the battery. If the above ideas hold, then the current should increase to about 200mA. Note, somebody here suggested a way to use an folded aluminum foil (8 folds) used to form a sandwhich of foil-paper-foil that can be used break the connections of a battery while sitting in a charger to provide two attach points (foil) for inserting an ammeter. See pic below:


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## Mr Happy (Jan 17, 2010)

*Re: Duracell CEF21 disassembled (modifications, anyone?)*

Here are high resolution images of each side of the circuit board to help with following the traces:


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## Mr Happy (Jan 17, 2010)

*Re: Duracell CEF21 disassembled (modifications, anyone?)*

I'm running the charger disassembled at the moment and using jump leads to connect from the charger to the battery. Last night I tried the experiment of connecting the AAA terminal to the AA terminal but it was unsuccessful. The AAA cell took about 5 hours to charge as normal. I'm not sure what went wrong; maybe my shorting lead was too long and too high resistance.

I am now charging an AAA cell directly from the AA connector as a reference test to see if that takes the expected two hours to complete.

Current measurements are difficult. While my meter sees steady voltages, the current through the cell appears to be pulsed and the meter doesn't respond fast enough to catch the values. (As I write this I think I might have a different meter with a max hold setting. Maybe that will do better.)

I don't _think_ the charging circuit is using a linear regulator. It think it is using a buck configuration with current sensing. For instance, the transformer leading from the mains power section appears to be feeding a set of eight power diodes (mostly buried in the "stuff" encapsulating the coils) but two of these diodes can be seen in the top view as D8 and D9. In the bottom view they are the two rows of eight thick round pads just north of the transformer.

Above these pads are four configurations of big coil, big capacitor, transistors, chips and other components (e.g. Q4, Q8, R5, C12 on the bottom view). Each of these configurations are what I think are the buck circuits. Just above R15 a thick trace leads back to near R5 and Q8. This I presume is an output feeding one charging channel.


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## Mr Happy (Jan 18, 2010)

*Re: Duracell CEF21 disassembled (modifications, anyone?)*

Well, my attempted modifications are failing 

I have tried two different methods of temporarily connecting the AA post to the AAA post. I have not got the resistance down to zero, but my second attempt got the voltage differential down to about 5 mV. Even so, this is not getting the charging current to rise much above 175 mA when connecting a cell directly to the AAA post. I have verified that when I connect an AAA cell directly to the AA post the charging current is 400 mA. Somehow the circuit seems to be detecting which charging post is in use regardless of my attempt to electrically join the AA and AAA posts. This is very puzzling.

I have been trying to avoid any destructive modifications or use of a soldering iron until I could verify that a planned modification would work, however I am now running out of ideas. What the circuit is doing such that it seems almost entirely insensitive to the resistance between the AA and AAA posts is a mystery.

On the other hand, I have further evidence for the Uniross Hybrio cells I call "hybriloops" being the same as eneloops. I noted that a Rayovac Hybrid reached a maximum voltage of 1.48 V at charge saturation, whereas the Hybrio reached 1.54 V. This latter voltage matches exactly what I observe from Eneloops and not from any other cell I have tested.

I have also noted that AAA cells of either Rayovac or Eneloop varieties do not give a very strong -dV signal. In both cases I saw the voltage reach a plateau and remain steady without decreasing as the cell temperature at the same time began to rise indicating full charge. I think that temperature sensing is more important for termination with AAA cells than with AA cells. 

Related to temperature sensing the CEF21 has a temperature sensor tucked inside each negative post right where it touches the battery and far away from heat generating components in the power supply. This would certainly help with generating a good temperature signal.


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## PeAK (Jan 18, 2010)

*Re: Duracell CEF21 disassembled (modifications, anyone?)*



Mr Happy said:


> Well, my attempted modifications are failing....the circuit is doing such that it seems almost entirely insensitive to the resistance between the AA and AAA posts is a mystery.../QUOTE]
> 
> Here's a reason to be _happier_:
> 
> ...


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## Mr Happy (Jan 18, 2010)

*Re: Duracell CEF21 disassembled (modifications, anyone?)*

Thank you. I noticed the LM339 yesterday, tried to follow traces and was forming the same idea that on/off control is involved. Therefore almost any voltage differential between the AA and AAA posts trips the comparator and flips the circuit into low current mode?

You have succeeded better than I did in following where the traces go. It's not easy when they keep jumping from one side of the board to the other. I shall examine your diagram with interest.


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## Mr Happy (Jan 18, 2010)

*Re: Duracell CEF21 disassembled (modifications, anyone?)*



PeAK said:


> The "AA" trace in the top left marked with yellow ultimately makes it way thru R13 to pin5 (positive input) of the LM339. Similarly the "AAA" trace marked in red makes it way through R12 to pin4(negative input).
> 
> When an AAA battery is placed in the charger, the 50mV signal causes pin2(marked in orange) to drive the output "*HI*" and signal the charging circuit to lower the current output. To have the charger put out a 400mA current, I suspect it would be as simple as configuring the outputs to put out a logic "LOW" (pins 1, 2, 13 and 14). This can be achieved on the input side or on the output side making a few selective cuts and joins. Try it out on one channel by using an Exacto knife to cut the orange trace (near R13 marking) and jumper a wire on the left hand side to pin 12 (ground pin) of the LM339.


If I'm not mistaken, the pin and trace you have marked in orange on the image is actually pin 3, V+? Pin 2 would be the next pin north, next to the first 3 of C33?


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## PeAK (Jan 18, 2010)

*Re: Duracell CEF21 disassembled (modifications, anyone?)*



Mr Happy said:


> If I'm not mistaken, the pin and trace you have marked in orange on the image is actually pin 3, V+? Pin 2 would be the next pin north, next to the first 3 of C33?



Mr Happy...you're absolutely right. I realized this after looking at the other 3 comparators this afternoon and decided to draw out the circuit. The outpus all come out of the top of the LM339 as positioned in your bottom view. You will see four traces, the second from left is V+, the other three are outputs with the other output coming out directly from pin#1.These outputs go to the ATMEL chip and I guess programme the current level. In the diagram below, I show this current source with the logic connection. Hope this helps:





Detect circuit for AAA/AA current selection
(Drawing courtesy of *OpenOffice Draw*)
​ Note: Diagram has comparator flipped...see post #26 and #27 for update
In the diagram, you see a red wire for when the AA battery is in the circuit. This puts both inputs at around 1.2V but the 2.2M will cause the negative input to be slightly higher than the positive input and the output will be a "LOW" logic. When the "green wire" is connected, the circuits works as described earlier. There is no hysteresis/"positive feedback" in the circuit and I will strike out those comments in the earlier post.

EDIT: The output traces can be cut either on the non-component side (top view) by cutting the respective purple traces and connecting the side going to the ATMEL chip to the ground plane. Just as easily, they can be cut on the component side and connected to the GND node. The leftmost charging bank output trace going to the ATMEL chip is the rightmost purple trace. These traces on the non-component side are shown in purple below:


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## Mr Happy (Jan 18, 2010)

*Re: Duracell CEF21 disassembled (modifications, anyone?)*

Thank you, nice diagrams. I shall reflect on what to do next. :thinking:


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## PeAK (Jan 19, 2010)

*Re: Duracell CEF21 disassembled (modifications, anyone?)*



Mr Happy said:


> Thank you, nice diagrams. I shall reflect on what to do next. :thinking:


You're most welcome but most of the thanks goes to Sun Microsystems that provided the OpenOffice Draw program. It is the first time that I've really tried it out and it is much better than the equivalent "drawing functionionality" provided within Microsoft Word...back to the CEF21 farm.

 Provided you are comfortable with surface mount components, the easiest modifcation would be to remove the 10K resistor going to the negative input: Pretty easy to taste a CEF21 charger pumping a sweet 400mA into AAA batteries.


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## Mr Happy (Jan 19, 2010)

*Re: Duracell CEF21 disassembled (modifications, anyone?)*

While I await my next move, there is another neat thing I discovered over the weekend. After I charged a Hybriloop up to 1.54 V I later attempted to put it back on charge. I found that the charger flashed the error indicator and refused to accept it. It evidently has a high voltage test. It would be appealing to think this is to prevent the overcharging of a fully charged cell, but I think perhaps it is more likely to reject an alkaline cell that might be placed in the slot.


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## PeAK (Jan 19, 2010)

*Re: Duracell CEF21 disassembled (modifications, anyone?)*



Mr Happy said:


> While I await my next move...


The following change to the circuit is the simplest to test in circuit but takes a bit more room than "10K removal mod" as component side clearances to the casing may be tight. It is also the most elegant if you change your mind and wish to UNDO the mod.





(drawing courtesy of OpenOffice program)
[EDIT: error found January 22/2010:See post #26/#27 below]
​ Tack a 270 Kohm resistor across R39 and then try a AAA in the leftmost bank. The current should be 400mA. The change pumps additional current through the bottom 10K resistor (toward the AAA battery) to generate a 60mV signal across it toward the comparator. This compensates for the 50mV drop of the 0.3 ohm resistor so that the net result is the positive [edit: negative] input terminal ending up at about 10mV higher than the negative [edit : positive] input terminal. This generates a logic HI [edit: "low" and sets the ATMEL/"current source" to 400mA. The only change is about 6uA of additional current flowing down from the 270K resistor and through the bottom 10K resistor that is then sunk by the AAA battery. The named of the output called HI_CURRENT.

EDIT: Corrected diagram follows all references to negative should be changed to posistive and vice-versa


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## Mr Happy (Jan 22, 2010)

*Re: Duracell CEF21 disassembled (modifications, anyone?)*

How about if I just connect pin 5 directly to ground? I can do this with a simple piece of wire which is easier for me to solder than a resistor, and it should force the output to logic low at all times. The data sheet says that all unused pins should be tied to the negative supply so this should be safe and harmless to do.

I also feel an inclination to bypass the 0.3 ohm resistors, just on principle.


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## Mr Happy (Jan 22, 2010)

*Re: Duracell CEF21 disassembled (modifications, anyone?)*

Fun with image manipulation 

While I wait to get the parts to modify the charger, I was having trouble following the traces on the dual-sided board where they duck through to the other side.

So to make life easier I produced a composite image with both sides overlaid and lined up with each other.

Here is the result. The first is the basic image, and the second has the AAA cell detection circuits traced out:









This should serve as helpful documentation for anyone else who wants to consider modifying the charger.


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## PeAK (Jan 22, 2010)

*Re: Duracell CEF21 disassembled (modifications, anyone?)*



Mr Happy said:


> How about if I just connect pin 5 directly to ground? I can do this with a simple piece of wire which is easier for me to solder than a resistor, and it should force the output to logic low at all times. The data sheet says that all unused pins should be tied to the negative supply so this should be safe and harmless to do.
> 
> I also feel an inclination to bypass the 0.3 ohm resistors, just on principle.


Nice effort on the pics. 

Your fix will work but a 10K resistor will *now* appear in parallel with the battery drawing about 0.15mA. I don't think it is a big deal but the fix below eliiminates that current and also give the comparator inputs the largest amount of margin (compare to the 270k fix).The 10k to be remove is the one that goes from the AAA terminal. The other way to confirm is to check the correct 10K is verify the connection (using ohmeter) to pins 5, 7, 9 and 11(EDIT: 4, 6, 8 and 10). These resistors are pointed out by the black lines in the image below:


EDIT: Figure removed due to ERROR in post #20 

The most straightforward mod is the *removal of the bottom 10K* going to the [EDIT:"negative"]  postive terminal, however, the complexity is knowing how to remove a surface mount component:

If you have steady hands, good eyes and two soldering irons you can do the following: 
Let both irons get hot and use them like you would if you were using them as a beginner would with chopsticks (i.e. one in each hand). Then pinch each iron on either side of the two ends of the surface mount 10K resistor and lift simultaneously. 






I would practice on some scrap board with surface mount components first, though.​Note: The downside with this "10k" fix is primarily one of reversing the change. It requires very steady hands and some more tricks/technique. Last, now that we "understand" the circuit, it does not make sense why your initial idea of shorting out the 0.3 ohm resistor does not work. I think it may have to do with the combination of the pulsing charge and the use of 'long wire'/'alligator clips' but a quick check would be to solder a wire directly across the 0.3 ohm resistor. The 10K mod will provide more margin in any case.


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## Mr Happy (Jan 22, 2010)

*Re: Duracell CEF21 disassembled (modifications, anyone?)*

I will certainly consider the idea of removing the appropriate 10k resistors when I work up enough confidence to try it. Or I will perhaps try cutting the tracks with an Exacto knife. My eyesight is the bother. I cannot see well enough with the unaided eye to do such detailed work.

Just in case anyone reading this thread is considering the same modification, I'm not sure you have picked out the correct resistors? I have circled my picks in the image below. The AAA battery post is the inner post with the three solder lugs.






As to why shorting the resistor didn't work, I think it is because of the difficulty getting a zero resistance current path. Even a few mV differential will raise the (-) input of the comparator higher than the (+) input and trigger the output low. In my test I got the differential down to ~5 mV but this is still too much.


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## PeAK (Jan 22, 2010)

*Re: Duracell CEF21 disassembled (modifications, anyone?)*



Mr Happy said:


> ...I'm not sure you have picked out the correct resistors? I have circled my picks in the image below. The AAA battery post is the inner post with the three solder lugs.
> ....



EDIT: See post below due to Errors in diagram in Post #20
 I made an *error by selecting R18* (The one we agreed on) and *should have picked R19*. You're choices are the resistors going to the positive terminal...NOT!!! The idea of cutting a trace is an even more direct mod similar to removing the 10K resistor. To reverse the mod, you need only scratch the protective coating off the trace and dab in a wire jumper. Cut it somewhere between the 0.3 resistor and the 10K.

I just realized why the short does not work. With current flow towards the AAA battery, the potential on the positive input will always be higher...in your case 5mV. This works out to a resistance of 0.028 ohms 
(i.e. 5mV/175mA)...pretty low and this is the result of the narrow width of the trace after the 0.3 ohms resistor (in parallel with your short). 

Good luck.


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## Mr Happy (Jan 22, 2010)

*Re: Duracell CEF21 disassembled (modifications, anyone?)*

I see where we seem to have a disconnect. In your circuit schematic in post #20 you show the negative input (pin 4) going to the AAA cell and the positive input going to the AA cell. However, when I follow the circuit traces that does not seem to be the case. For instance negative input #2 at pin 6 (orange) appears to connect to the AA cell and positive input pin 7 (red) to the AAA cell. Similarly (-) pin 8 (purple) connects to the AA cell and (+) pin 9 (violet) to the AAA cell. This is consistent in all four banks.

What this means is that when current flows through the 0.3 ohm resistors to an AAA cell the voltage on the down side drops below the voltage on the up side. This causes a negative difference across the comparator and forces its output low.

When an AA cell is connected the output should therefore be high. I can test this perhaps with a meter later.

[Edit: I have measured this to confirm. The positive supply to the LM339 is 5 V. When an AA cell is on charge the output at pin 2 is high at 5 V and when an AAA cell is on charge the output is low at 0 V.]

If I remove the resistors or break the connection on the AAA circuit (e.g. R18) the comparator will lose the signal from an inserted AAA cell and should keep the current supply in the AA mode...


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## PeAK (Jan 22, 2010)

*Re: Duracell CEF21 disassembled (modifications, anyone?)*



Mr Happy said:


> ...Just in case anyone reading this thread is considering the same modification, I'm not sure you have picked out the correct resistors?



Mr Happy, I messed up again. The nice diagram had the comparator flipped. This only affects the sense of the output sense of the comparator BUT also means that whenever I referred to the "negative input", I really meant the positive input. In the diagram, it still is the bottom resistor and this does not change. The updated diagram with the "CUT" mod is shown below. I think this is the way most people should do the change.






I apologize for being as clear a mud. Lesson: Beware of nice diagrams.

EDIT: Just saw your post above...it is 100% correct. Thanks for the feedback and my apologies again.

P.S. I'll expect to see a charger working 400mA into AAA batteries within the hour...slice and dice


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## Mr Happy (Jan 22, 2010)

*Re: Duracell CEF21 disassembled (modifications, anyone?)*

I'm glad we've converged.



PeAK said:


> I think this is the way most people should do the change.


I think "most people" includes me. Some of those resistors are squeezed in tightly next to other components with small clearances. These pretty photographs don't quite convey how tiny this stuff is...


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## Turbo DV8 (Jan 22, 2010)

*Re: Duracell CEF21 disassembled (modifications, anyone?)*



Mr Happy said:


> After I charged a Hybriloop up to 1.54 V I later attempted to put it back on charge. I found that the charger flashed the error indicator and refused to accept it.


 
The Mobile Charger does this also if you insert a fully charged cell.


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## PeAK (Jan 23, 2010)

*Re: Duracell CEF21 disassembled (modifications, anyone?)*



Turbo DV8 said:


> The Mobile Charger does this also if you insert a fully charged cell.


Turbo...for a second I thought you beat Mr. Happy to the punch. My 'Mini Charger" also flashes with a freshly charged battery. My first smart charger was a RS 23-425 that did the same with a pair of batteries. The rejection of a freshly charged pair of batteries formed my "How did it know" test for a smart charger for a while but I think Mr. Happy is right in that it is part of the Alkaline battery test...still you never know: they might add a starting condition whereby they look at the initial voltage to be greater than say about 1.4 V and look at the delta with a pulse of current.


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## PeAK (Jan 23, 2010)

*Re: Duracell CEF21 disassembled (modifications, anyone?)*



Mr Happy said:


> ...[Edit: I have measured this to confirm. The positive supply to the LM339 is 5 V. When an AA cell is on charge the output at pin 2 is high at 5 V and when an AAA cell is on charge the output is low at 0 V.]



The suspense is mounting and by my count you've "measured twice"...time to "cut" 

For the inputs/resistors controlling the output on pin2, it seems that you would need to cut the trace going to R13. I've identify a good spot to cut this trace in the figure below:






The pink line pointing to the blue trace is a good place to cut using an exacto knife to re-program the leftmost bank. The bank next to it can be re-programmed by cutting the red trace shown by the pink arrowed line.

It would be neat if you left your charger in this state as you could have the two rightmost banks behave as it did before (175mA) with AAA batteries and the two leftmost banks charging at a higher current(400 mA).


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## Mr Happy (Jan 23, 2010)

*Re: Duracell CEF21 disassembled (AAA improved charging modification?)*

OK, I've made the mod on one channel and I'm charging a cell to test it. We'll see what happens.


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## PeAK (Jan 23, 2010)

*Re: Duracell CEF21 disassembled (AAA improved charging modification?)*



Mr Happy said:


> OK, I've made the mod on one channel and I'm charging a cell to test it. We'll see what happens.



In case we need to wait :shakehead5 hours :shakehead, can you do an early test on "the cut" to see if the output of pin#2 on the LM339 checks out to be what you expected ?


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## Mr Happy (Jan 23, 2010)

*Re: Duracell CEF21 disassembled (AAA improved charging modification?)*



PeAK said:


> In case we need to wait :shakehead5 hours :shakehead, can you do an early test on "the cut" to see if the output of pin#2 on the LM339 checks out to be what you expected ?


No need to wait 5 hours , I have a meter on the cell and the voltage is going up at the 400 mA rate . It's presently 20 minutes to the expected termination. Will it terminate the charge on cue, that is the question?


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## Mr Happy (Jan 23, 2010)

*Re: Duracell CEF21 disassembled (AAA improved charging modification?)*

OK, it terminated.

For this test not only did I break the trace leading to the input of the comparator, but I also bridged the AAA charging post to the AA post with a soldered in jumper. Just for neatness.

Here are the results:

Cell under test ......................................... AAA "Hybriloop" (eneloop clone)
Time to termination ..................................... 2h20m
Peak charging voltage prior to termination .............. 1.581 V
Charging voltage registered just prior to termination ... 1.576 V
Estimated −∆V signal .................................... 5 mV
Maximum cell temperature ................................ 34°C
Cell voltage just after termination ..................... 1.54 V
 
I'd say the test was successful! :thumbsup:


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## PeAK (Jan 23, 2010)

*Re: Duracell CEF21 disassembled (AAA improved charging modification?)*



Mr Happy said:


> OK, it terminated...I'd say the test was successful! :thumbsup:



Congratulations!
I read your previous post around 5pm and the results were due around 5:30pm. I checked in around 5:45pm and no results but I had faith and this tune in my head from my days as a wee lad watching the "Bugs Bunny/Road Runner Hour" at 6pm:

 Overture, curtain, lights 
 This is it, the night of nights 
 No more rehearsing and nursing a part 
 We know every part by heart 
 Overture, curtains, lights 
 This is it, we'll hit the heights 
 And oh what heights we'll hit 
 On with the show this is it 

 Tonight what heights we'll hit 
 On with the show this is it 

​It was neat to see all the data including the temperature info. How does 34 degrees feel to the hand ?

​


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## Mr Happy (Jan 23, 2010)

*Re: Duracell CEF21 disassembled (AAA improved charging modification)*

34 degrees feels slightly warm to the touch, a bit warmer than room temperature but not much. Like a metal object that someone has been holding for a while.

I have gone ahead and modified all four channels and I'm just discharging a set of four Rayovac Hybrids to do a full charging test. I have three CEF21 chargers so I don't mind experimenting on one in an attempt to improve it.

On comparing the innards of this charger to the CEF23 in another thread, this one seems by far the most complex inside.


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## PeAK (Jan 23, 2010)

*Re: Duracell CEF21 disassembled (AAA improved charging modification)*



Mr Happy said:


> ...I have gone ahead and modified all four channels and I'm just discharging a set of four Rayovac Hybrids to do a full charging test. I have three CEF21 chargers so I don't mind experimenting on one in an attempt to improve it...


Good to see you embolden by success and on the road to gathering more data on your modifed chargers results with different AAA batteries.​


Mr Happy said:


> ...I also bridged the AAA charging post to the AA post with a soldered in jumper...


The effect of series resistance is going to small to a current source in your case because it only needs to account for a small voltage increase to keep current constant. You can measure the value between the AA and AAA terminal using an ohmeter but even if it were 3x the value of the 0.3 ohm resistor, lets say 1ohm, the voltage drop would only be 0.4A * 1 ohm =0.4V. For a 5V supply voltage, this would add to the 1.5V at termination and require the current source to work up to 1.9V...shouldn't be much of a problem. But as you say, putting in the short should not hurt.

Before making the "short" mod, you can also measure the voltage at both the AA terminal and the AAA terminal to see the voltage delta. If you leave it out the short, this voltage can provide an easy way to monitor the current via the resistance info.​


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## Mr Happy (Jan 23, 2010)

*Re: Duracell CEF21 disassembled (AAA improved charging modification)*

I'm also thinking about the bad cell detection logic and charge termination logic that work with voltage measurements too. By shorting the 0.3 ohm resistor I make an AAA cell look as much like an AA cell to the charger as possible, especially in light of the increased current that would be flowing through the resistor after the modification.


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## Mr Happy (Jan 24, 2010)

*Re: Duracell CEF21 disassembled and modified for improved charging of AAA*

Now here is interesting. I set the four AAA Rayovac Hybrids to charge in the reassembled charger. The charge did terminate automatically for each cell, but at very unequal times spaced between 2h 10m and 2h 40 m. All of the cells reached about 48°C prior to termination.

Oddness was afoot with these cells. For instance the last cell spent about 15 minutes at least at a temperature of 48°C with the voltage hovering around 1.471 V before the charger eventually decided to end the charge. I did not observe any detectable −∆V signal as I did with the Hybriloop, so I presume the charger selected some other termination criterion.

After I discharge the Hybrids I am going to charge them in the GP PowerBank 1 hr charger and see what it makes of them.


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## PeAK (Jan 24, 2010)

*Re: Duracell CEF21 disassembled and modified for improved charging of AAA*



Mr Happy said:


> Now here is interesting. I set the four AAA Rayovac Hybrids to charge in the reassembled charger. The charge did terminate automatically for each cell, but at very unequal times spaced between 2h 10m and 2h 40 m. All of the cells reached about 48°C prior to termination.
> 
> Oddness was afoot with these cells. For instance the last cell spent about 15 minutes at least at a temperature of 48°C with the voltage hovering around 1.471 V before the charger eventually decided to end the charge. I did not observe any detectable −∆V signal as I did with the Hybriloop, so I presume the charger selected some other termination criterion...



Interesting that one terminated 10 minutes faster than your first experiment but with a bit more heat. They make a good group of batteries to determine the signature of why the charger stopped charging at a 0.5C rate.

Some random thoughts:


Previous to your mod, the rate was 0.218C and gave a ambiguous −∆V signal to the charger even with eneloops but the battery probably could not generate enough heat/temperature to reach 48°C. The message here seems to be that if a charger is relying on a backup termination scheme, then, it should kick in before too much excess charge happens. Your modifed chargers seems to do this.
Possibly the charger uses "0 slope" to terminate when above a certain temperature. I used a 0.14C rate on a fully discharged Energizer 2500 battery that increased the voltage at about 1mV every six minutes (middle of charge cycle) and it never terminated until the 10 hour time out function kicked in. This is as close as you might get to "0 slope" conditions.
I guess one could apply a heat gun after one hour and raised the ambient above 48°C to see if backup termination scheme is temperature. The opposite experiment of putting a fan could also tell you with the danger of putting in a cycle of extreme overcharge should it be defeating the temperture termination. If it terminates, as before, then it probably is "0 Slope" termination.
48°C is 118°F (20 degrees warmer than the human body) and can be found in places in this world. How would you classify the temp to the touch?
One can get a better appreciation of what the Maha engineers were up against when they try to determine a termination scheme for all sorts of NiMH batteries...some with very weak to no −∆V signal. If the last battery hovered around 1.48V, even, the Maha C9000 would have heated the battery up to beyond 48°C.


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## Mr Happy (Jan 24, 2010)

*Re: Duracell CEF21 disassembled and modified for improved charging of AAA*

I would say 48°C feels toasty warm but still comfortable to the touch.

After the Rayovacs I found a set of Kodak Pre-Charged AAA that had been fully charged a long time ago and put in storage. They were reading about 1.29 V. I put them on the modified charger and they all terminated at about the same time after 10 or 15 minutes on charge and with a temperature not much above 30°C. The Kodak cells also reached above 1.54 V prior to termination.

I discharged the Rayovac Hybrids at 500 mA on the C9000 and got readings of about 650 mAh as is usual for these cells. I discharged the Kodaks at the same rate and got readings of just under 800 mAh, similar to Eneloops.

In this case I think the problem lies mostly with the Rayovac cells. Either the breed in general or these four in particular have higher internal resistance, lower voltage, less pronounced −∆V and overall just do not seem to perform as well.

The Rayovacs are just finishing up a test charge on the GP PowerBank 1 hr charger. Three cells have terminated after 50 minutes but one is still going. I'm not sure if it is the same one that also took a long time on the CEF21. The one that is still charging is up to 65°C now (the others reached 50-60°C prior to termination). As I write it has just stopped at 55 minutes and 68°C. This temperature can be described as very hot, uncomfortable to touch for more than a couple of seconds, and emitting a "hot" smell.


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## Turbo DV8 (Jan 24, 2010)

*Re: Duracell CEF21 disassembled and modified for improved charging of AAA*



Mr Happy said:


> Now here is interesting... the four AAA Rayovac Hybrids... did terminate automatically for each cell, but at very unequal times spaced between 2h 10m and 2h 40 m.


 
FWIW, I am finding my AAA ROV Hybrids to be widening out all over the board in terms of being able to terminate at previously reliable rates, rates of self-discharge, or just plain crapping out altogether. Maybe can just chalk your observation up to the ROV Hybrid AAA's not being as stable over time as the Eneloops?


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## PeAK (Jan 24, 2010)

*Re: Duracell CEF21 disassembled and modified for improved charging of AAA*



Mr Happy said:


> ...a set of Kodak Pre-Charged AAA that had been fully charged a long time ago and put in storage. They were reading about 1.29 V. I put them on the modified charger and they all terminated at about the same time after 10 or 15 minutes on charge and with a temperature not much above 30°C. The Kodak cells also reached above 1.54 V prior to termination.


Pretty neat as a Maha would still be topping them up for a while



Mr Happy said:


> ... The Rayovacs are just finishing up a test charge on the GP PowerBank 1 hr charger. Three cells have terminated after 50 minutes but one is still going. I'm not sure if it is the same one that also took a long time on the CEF21. The one that is still charging is up to 65°C now (the others reached 50-60°C prior to termination). As I write it has just stopped at 55 minutes and 68°C. This temperature can be described as very hot, uncomfortable to touch for more than a couple of seconds, and emitting a "hot" smell.


It looks like these batteries best be charged on the C9000. They have similar issues to the Energizer 2500 batteries but with better shelf life. For those without a C9000, a way to use them would be to fully discharge them and to put them on a timed charge putting out about 1.6C.





Turbo DV8 said:


> FWIW, I am finding my AAA ROV Hybrids to be widening out all over the board in terms of being able to terminate at previously reliable rates, rates of self-discharge, or just plain crapping out altogether. Maybe can just chalk your observation up to the ROV Hybrid AAA's not being as stable over time as the Eneloops?


Are these the same as the Rayovacs 4.0 ? I'm sure that as each charge cycle misses termination and heats the battery, the next charge cycle will have an even tougher time terminating.


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## Mr Happy (Jan 24, 2010)

*Re: Duracell CEF21 disassembled and modified for improved charging of AAA*



PeAK said:


> Are these the same as the Rayovacs 4.0 ?


As far as we know, the Rayovac 4.0 and the Rayovac Hybrid are the same cell inside.



> I'm sure that as each charge cycle misses termination and heats the battery, the next charge cycle will have an even tougher time terminating.


So you think perhaps allowing one to heat up to 68°C was not a good idea? :devil:


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## PeAK (Jan 24, 2010)

*Re: Duracell CEF21 disassembled and modified for improved charging of AAA*



Mr Happy said:


> ...So you think perhaps allowing one to heat up to 68°C was not a good idea? :devil:


I'm pretty sure the priorities of the Maha engineers was to avoid both the excess charge and heat when they revised the firmware of the C9000. So you can buy the most sophisticated/$$$ charger to use with the worst performing batteries or else buy cheaper chargers to be used with "better" batteries. The Duracell Chargers seem to add enough sophistication to allow you to use some of the "bad" stuff.

Personally, from your test results, it seems like a green light to have your reamaining two CEF21 units "modded". As this thread's content has about 96% of it's post contributed by two people, we could strip down all the posts and offer a *CEF21 modification service *and be infamous


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## Mr Happy (Jan 24, 2010)

*Re: Duracell CEF21 disassembled and modified for improved charging of AAA*

You understand :devil: means it was a joke, right? 

Another data point here. I just charged the set of four AAA Kodak Pre-Charged cells from empty. They all terminated at 2h 30m ± 5m at a maximum cell temperature of about 47°C. That's good and consistent and still relatively cool.

So yes, I'd say the modification is a success.

I do have in mind now to produce a single post with detailed step by step modification instructions including pictures and I will reference that from the first post in the thread when I do so. I may get to that later today. [Edit: Done; see post #50 below.]

I may modify the other chargers or maybe not. We'll see. I really don't have that many uses for AAA cells. The main uses are my Harmony remote and perhaps a couple of small lights. Where size is not an issue AA cells are far more practical than AAA cells.


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## verge (Jan 24, 2010)

*Re: Duracell CEF21 disassembled and modified for improved charging of AAA*

Thank you very much Mr. Happy for that Duracell CEF21 modification experiment.
I have the CEF21 and CEF23, but I like the CEF21 better for its power gauge lights. 
I like the columns of lights moving upward as the battery gets closer to full charge.
It's better than the single light on CEF21 that changes its color to green indicating full charge.
The power gauge lights gives me a sense of time when the battery is halfway and about to reach its full charge. Although it seemed that the time it takes to finish from halfway is faster than from start to halfway with CEF21's power gauge, it still gives me a sense of time in anticipating when its going to reach full charge.
(Off topic) I wish MH-C9000 will also have some sort of power gauge for each battery along with the numbers shown on the screen.


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## Mr Happy (Jan 24, 2010)

*Re: Duracell CEF21 disassembled and modified for improved charging of AAA*

Yes, it's a nice charger but you should be aware that the "power gauge" is actually more of a "progress gauge". The second red light comes on exactly two hours from the start of charge, and the third red light exactly two hours after that. The finishing green light is the only one that really depends on the state of the battery. It looks nice and gives you a rough countdown timer, but it doesn't really know how full the charge is.

On the C9000 you have a timer that gives you the same information, and better than that you have the voltage reading. Once you know the charging profile of a battery you can use the displayed voltage to give you a very accurate estimate of the time to go.


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## Mr Happy (Jan 25, 2010)

*Re: Duracell CEF21 disassembled and modified for improved charging of AAA*

Drawing together the various parts of this thread, here are step by step instructions for modifying a Duracell Power Gauge or Indicator charger model CEF21 so that it charges both AA and AAA cells at the higher rate of ~400 mA. The benefit of this modification is that it will produce faster charging and more reliable charge termination with AAA cells.

Step 1: Turn the charger upside down and remove the four rubber feet by lifting them with a fingernail. Underneath are four cross head screws to be removed. While removing the screws hold the case together with your other hand to stop it coming apart prematurely. Keep the screws and the rubber feet safe.







Step 2: Carefully remove the lower half of the case while leaving the circuit board attached to the upper half of the case. Inside it should look like this:






Step 3: Using a small, sharp craft knife and a magnifier, carefully cut through the circuit traces at the locations shown.






Step 4: (Optional) For maximum circuit efficiency you can bridge the AA posts to the AAA posts of each charging circuit, as illustrated below. The modification should still work without this last step and if you are not confident with a soldering iron you can skip it.






Step 5: Reassemble the case and test. After the modification an 800 mAh AAA cell should take about 2.5 hours to charge instead of the 5-6 hours it would previously have taken.


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## march.brown (Jan 26, 2010)

Mr Happy said:


> My goal is to modify the charger so that AAA cells get charged with the same 400 mA that AA cells get.


 

I might be missing something here, but ------

Would it not be easier to use the AA cell slots to charge the AAA cells in, by using a ball-bearing or magnet spacer ? ... It would be easy to make a spacer by cutting a piece of brass rod to the right size ... This way, you have the choice of two AAA charging currents and the charger is still in its original specification should you ever want to sell it.
.


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## PeAK (Jan 26, 2010)

march.brown said:


> I might be missing something here, but ------



Mr Brown,
For Flashaholics, it all comes down to *play value*. We get to pull out our screwdrivers, meters, Xactor knives, soldering irons, and then document the process with our digital cameras. The other aspect to "playing" for my generation (Seventies) is making up for "lost play time" when the leisure time meant playing the new vinyl LP for the whole entire month. Repeat process of waking up early to head downtown to pick up the next new release.

If the above sounds all confusing, the you can wax on this poem and ponder life.

I was an "enlightened" member, once. 
PeAK


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## Bright+ (Jan 26, 2010)

*Re: Duracell CEF21 disassembled (modifications, anyone?)*

Another option is to simply jumper the 0.3 ohm resistor, so that the mV/A sent to feedback is the same for both AAA and AA.


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## march.brown (Jan 26, 2010)

PeAK said:


> Mr Brown,
> For Flashaholics, it all comes down to *play value*. We get to pull out our screwdrivers, meters, Xactor knives, soldering irons, and then document the process with our digital cameras. The other aspect to "playing" for my generation (Seventies) is making up for "lost play time" when the leisure time meant playing the new vinyl LP for the whole entire month. Repeat process of waking up early to head downtown to pick up the next new release.
> 
> If the above sounds all confusing, the you can wax on this poem and ponder life.
> ...


.
Thank you for your comments and making me realise that I am missing out on playing ... I am in my seventies so I remember LPs and the 78s too ... I remember studying Digital Computers and building up gates before there were Integrated Circuits ... As I was finishing my course of study, it was possible to buy ICs with whatever gates you wanted ... Now that was progress but not as much fun.
.
Keep up the good work and play-on.
.


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## PeAK (Jan 26, 2010)

march.brown said:


> .
> Thank you for your comments and making me realise that I am missing out on playing ... I am in my seventies so I remember LPs and the 78s too ...



I think Roberto Benigni said it best:

_“First I must thank my parents for giving me the greatest gift of all,” he said, then he paused for effect and dropped the bomb, “*poverty*.”_


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## Mr Happy (Jan 26, 2010)

*Re: Duracell CEF21 disassembled (modifications, anyone?)*



Bright+ said:


> Another option is to simply jumper the 0.3 ohm resistor, so that the mV/A sent to feedback is the same for both AAA and AA.


You might think so, mightn't you? However this option does not work when tested. Read the whole thread for some indications as to why...


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## PeAK (Jan 30, 2010)

*Re: Duracell CEF21 disassembled and modified for improved charging of AAA*



Mr Happy said:


> Drawing together the various parts of this thread, here are step by step instructions for modifying a Duracell Power Gauge or Indicator charger model CEF21 so that it charges both AA and AAA cells at the higher rate of ~400 mA. *The benefit of this modification is that it will produce faster charging and more reliable charge termination with AAA cells....*


Nice summary. I thought I put a couple of before and after images showing the change to the charge profile with an increase charge current to *show the benefit*. For those unfamiliar with smart chargers, they depend upon the formation of a bump at the end of the charge. I came across these pics from a thread (see link below after pics) from SilverFox after following TakeTheActive's signature line. The ideas are incorporated in this modification to the CEF21:

Before:





After:






Take a look at the pitfalls of Slow Charging by SilverFox. If you want to see if your charger can generate and detect "this bump" in less that 15 minutes, try this test.


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