# The anatomy of a Protected Battery



## HKJ (Jan 13, 2010)

I had a dead 18650 battery and wanted to get some more out of it, this is the result:

[size=+3]The Anatomy of a Protected Battery[/size]
Most batteries has some build in protection, usual it is only a pressure valve, but some batteries needs more than that for protection, this is especially true for some LiIon batteries (LiCoO2). Here I have dissected a AW 18650 battery to see the extra protection.







The battery is a 18650 battery, with this name it is supposed to be 18 mm in diameter and 65 mm long. These measurements do not fit reality completely, the battery is 18.4 mm in diameter and 67.4 mm long, the reason for the extra length and extra diameter will be obvious soon. 






The holes in the plus pole of the battery is the exhaust from the pressure valve in the battery, this can be seen on many types of batteries. Also hidden beneath the plus is a temperature fuse (Called a PTC resistor), but it cannot be seen here.
Note: This protection is enough for some manufacturer to call a battery protected, but a phrase like "pcb protection" or "IC protection" does cover a battery with full protection.












Note the narrowing on the backend of the battery and it also looks like there is something on the side of the battery. Both are signs that this battery has a electronic circuit in the back and usual this circuit is the extended protection. For standalone LiIon batteries (LiCoO2) it is very important that this protection is present. In packs with multiple cells this circuit is usual common for the pack and not mounted in each cell.
Note: Cell is a battery with only one "battery" in it, battery is a collection of cells but also used about a single cell (Does this sentence make sense?).









In this picture I have removed the wrapper around the battery and the circuit at the bottom of the battery can be seen, together with the wire on the side of the battery.












The wire is connected to the plus pole on the battery and the other end goes to the circuit in the bottom of the battery. The went holes, from the pressure valve, can also easily be seen here, including two more.












The wire is soldered to the circuit at the bottom and another wire goes from the circuit to the bottom of the battery, i.e. the (internal) minus pole. The (external) minus pole of the battery is the backside of the circuit, not the minus pole on the cell.






In this picture I have collected all the parts from the battery, the actual 18650 cell in a metal shell, the protection circuit that is mounted at the minus pole of the cell and various isolation pieces and spacers, together with the black wrapper that is placed around everything.
Measuring the cell, without wrapper, wire and circuit, it is exactly 18 mm in diameter and only 64.7 mm long, i.e. the 18650 specification fits.












One these pictures I show some different protection circuits, the last one is for a smaller battery (The scale is different, I have zoomed close on the last picture, all parts looks bigger).
This cirucit usual protect against over discharge, over charge, and to high current drain (Short circuit).









The protection circuit seen from the backside, i.e. the actual/external minus pole on the protected battery. As can be seen, one of the circuits has an extra metal plate on the back of the circuit, to make the minus pole more durable.












The circuit has two important elements, the blue circle is around the controller chip and the red circle is around the switch that is used to connect/disconnect the battery.

Measuring on the protection circuits I found:
AW:
Current consumption: 4.5 uA, i.e. it will discharge a 2000mAh battery in 50 years
Overdischarge will disconnect at 2.5 volt, but will only reconnect if the battery goes above 3 volt.
Overcharge will disconnect at 4.26 volt and will reconnect when battery is removed from charger.
Voltage drop in circuit at 1 amp and 2.9 volt battery voltage: 25mV

The other big circuit:
Current consumption: 4.2 uA
Overdischarge will disconnect at 2.5 volt, but will not reconnect again except with external voltage (i.e. a charger).
Overcharge will disconnect at 4.26 volt and will reconnect when battery is removed from charger.
Voltage drop in circuit at 1 amp and 2.9 volt battery voltage: 30mV

The small circuit:
Current consumption: 3.9 uA
Overdischarge will disconnect at 2.5 volt, but will not reconnect again except with external voltage (i.e. a charger).
Overcharge will disconnect at 4.26 volt and will reconnect when battery is removed from charger.
Voltage drop in circuit at 1 amp and 2.9 volt battery voltage: 60mV

The above measurements are only valud for the circuits I have measured on, but gives an indication about what to expect from LiIon protection circuits.


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## nfetterly (Jan 13, 2010)

Interesting post - that's what I am getting for my $$ !

Thanks, Neale


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## dirtybore (Jan 13, 2010)

Cool! Very well done. :goodjob:Great photos too.


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## csshih (Jan 13, 2010)

aw.. I was hoping you'd disassemble the 18650 cell itself! great pics of the circuit!


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## HKJ (Jan 13, 2010)

csshih said:


> aw.. I was hoping you'd disassemble the 18650 cell itself! great pics of the circuit!



I tried to open the top, but my tools was not really sufficient to do it in a orderly manner (I do not consider a hacksaw orderly in this case ).
But the main purpose was to show the protection circuit and that succeeded.


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## Lightcrazycanuck (Jan 13, 2010)

Excellent job HKJ.:twothumbs

The pics are awsome.:thumbsup:

lovecpf


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## alfreddajero (Jan 13, 2010)

I always wondered as well but didnt want to disect any of the batteries that i had. Thanks for clarifying the makeup of the protection circuit and +10 for the great pics.


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## JaguarDave-in-Oz (Jan 13, 2010)

A very enlightening post. I have wondered how such an arrangement all went together whilst remaining so compact and thanks to you I now know.


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## Conte (Jan 13, 2010)

:twothumbs


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## K_Labs (Jan 14, 2010)

Great post. I always wondered about that. I was about 2 make a new thread maybe you could answer my question. I have 2 of the exact same batteries but mine aren't disected. They stopped working all together today. They are protected cells and I checked them out with a voltage meter.... Nothing. Did I discharge them so much that the protection stopped them from putting out power? Or did I kill them both?


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## alfreddajero (Jan 14, 2010)

Did you try putting them back on the charger...it seemed that you tripped the overdischarge protection circuit and in order to reset it the cell needs to go back on the charger. I would put the cell on the charger and wait 2-5 minutes and then take a voltage reading then.


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## LuxLuthor (Jan 14, 2010)

I guess my thread "Photos of Protected Lithium Batteries" got too old to be found.


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## K_Labs (Jan 14, 2010)

Ty will let you know the result when I get a new charger. I lost my old one


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## Vesper (Jan 14, 2010)

Nice photos and info. Thanks - I enjoyed it. :thumbsup:


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## HKJ (Jan 14, 2010)

I have added some measurements on the protection circuit.
One interesting piece of data showed up, the protection circuit does not have any significant influence on the self discharge.


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## alfreddajero (Jan 14, 2010)

Thanks for that tid bit.....i wonder then what can cause it, especially if your like me which has more then 2 batts per light that i own. The lights that i edc i tend to rotate the batts out every 2 weeks or should i do it sooner then that.


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## K_Labs (Jan 22, 2010)

Well I got a Ultrafire 139 charger yesterday and it was working fine flashing light every 2-3 seconds (I didn't count). Left my batteries on there for about 5 mins tested and they are good 2 go again. Charged them up to about 4.2v is that right? Gotta love those protected cells. 

On the other hand. My charger stopped doing the 2-3 second flash and I think it's busted or something. I bought it from DX. Any1 else had this problem?


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## sqchram (Jan 22, 2010)

csshih said:


> aw.. I was hoping you'd disassemble the 18650 cell itself! great pics of the circuit!


 
Yes! Same here.


... at least put a .50 round through it!


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## alfreddajero (Jan 22, 2010)

K_Labs said:


> Well I got a Ultrafire 139 charger yesterday and it was working fine flashing light every 2-3 seconds (I didn't count). Left my batteries on there for about 5 mins tested and they are good 2 go again. Charged them up to about 4.2v is that right? Gotta love those protected cells.
> 
> On the other hand. My charger stopped doing the 2-3 second flash and I think it's busted or something. I bought it from DX. Any1 else had this problem?


 
When its done charging it should stay green.......you will only get the flash if its charging the cells.


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## K_Labs (Jan 23, 2010)

Yea it flashes red now constantly with or without batteries.


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## alfreddajero (Jan 23, 2010)

Send them an email about an RMA.......i would stop using it before something bad happens.


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## Capo_au (Jan 23, 2010)

> Measuring on the protection circuits I found:
> AW:
> Current consumption: 4.5 uA, i.e. it will discharge a 2000mAh battery in 50 years
> Overdischarge will disconnect at 2.5 volt, but will only reconnect if the battery goes above 3 volt.
> ...



Would I be right in assuming that if the over discharge disconnection kicks in then damage has already been done to a AW LiCoO2 cell?

Sorry if this is stating the obvious, i'm still trying to get up to speed on the different lithium chemistries.


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## K_Labs (Jan 25, 2010)

alfreddajero said:


> Send them an email about an RMA.......i would stop using it before something bad happens.


 
Yea good idea. It's a good thing I have 2


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## The Dane (Jan 25, 2010)

So i took a dead cell from a PC bat and heres the story in pictures:

Heres the patient and the tools for dissection





I first took 3 cuts on the mill to open the steel hull








Then i had to recut the top




The innards




The fartvalve sorry gasvent




Here it is the complete electrolyte




Wrapped around an alu tube to get the disered shape




"Between" the layers a sheet of copper @6x70cm or @2½x27½"





Under the intire ordeal a destinct stench of ether was pressent and at the wery first cut a clear liquid bubbeled out of the cell.

The brown stuff i think is the electrolyte and it is not flamable at all!




The ultrathin plastic film burns poorly, like a wet fart




The copper does'nt burn at all, who would have guessed that:duh2:




The film with lithium on




And by prodding it with a small propane burner i made it fart a couple of times like a sparkler, but no constant selfcontaining burn at all. Some nasty smell arose from this sacrifice to the electronic goods




And that ladies and gents, is another perfect served dish from hells kitchen:wave:


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## rayman (Jan 25, 2010)

Great thread :twothumbs. Always wanted to know what is inside there.

rayman


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## mikevelarde (Jan 26, 2010)

very informative!!!:twothumbs


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## Conan (Jan 26, 2010)

mikevelarde said:


> very informative!!!:twothumbs



+1! lovecpf


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## zipplet (Feb 6, 2010)

Excellent thread, thank you to both of you for taking these batteries apart. I was especially interested in the Li-ion cell dissection, being too chicken to ever do that myself!


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## WebWalker (Feb 8, 2010)

Excellent presentations gentlemen.
Learned a lot.


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## Rommul (Feb 9, 2010)

HKJ is there any possibility that you could reuse these protection circuits on other cells?


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## HKJ (Feb 10, 2010)

Rommul said:


> HKJ is there any possibility that you could reuse these protection circuits on other cells?



If you have the equipment to mount the circuit (Spot weld the connections), I believe it is possible. You can also get new circuits from DX.


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## NutSAK (Feb 11, 2010)

What did these poor 18650's ever do you you guys? 

Great info, thanks! 

Is there a shrink-wrap material that can be used as a replacement for the original wrapper? I have an AW that is developing a split in the wrapper.


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## The Dane (Feb 11, 2010)

NutSAK said:


> What did these poor 18650's ever do you you guys?
> 
> Great info, thanks!
> 
> Is there a shrink-wrap material that can be used as a replacement for the original wrapper? I have an AW that is developing a split in the wrapper.



Think RC, they shrink wrap all the time


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## NutSAK (Feb 11, 2010)

The Dane said:


> Think RC, they shrink wrap all the time



Thanks! I wasn't aware of that, and now I see many sources.

Is this material thin like the original though, or thicker like wire shrink wrap? I don't want to run into any fitment issues.


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## The Dane (Feb 11, 2010)

Most of the tuf i have bought is thin, the trick is selecting wrap that just fits. When it shrinks it thickens, doh rocket sciense:tinfoil:


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## kosPap (Jan 23, 2016)

HKJ I have a question.

I need to amke some button top 18650 umkprotected batteries.
I was thinking of getting protected ones, removing the wrap, the protection circuit and cut the wire as close to its root (if safe). the rewrap.

Question is, is the added button solidly mounted on the battery top, or is it easily removable if the second wrapper is removed?

edit: I just found ths picture of yours. is it like this always?


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## HKJ (Jan 23, 2016)

kosPap;4826485edit: I just found ths picture of yours. is it like this always?
[IMG said:


> http://www.lygte-info.dk/pic/battery/DSC_6239.jpg[/IMG]



No, there are two way to do button tops, the above is one way. The other way is to weld the top directly to the plus pole of the battery.


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