Removing protection circuits and voltage

[Knife Collector]

I was a member here long time ago, but did not recognize my email so had to make new account.. anyway..
I fully charged some 18650s, then removed the protection circuits for a project. When I installed them they only showed half charge.
I checked with volt meter, and they showed about 3.75. I then checked the batteries that still had the circuits, and they showed 4.2.
I tried both in my chargers, a BT-3100 V2, and an Intellicharger i4. Both show the one with the circuits as full, and the unprotected as needing a charge.
I did a capacity test when first charging with the 3100 and it showed all the batteries at 3280-3360 (when they all had protection circuits) for Panasonic 3400s.
So could be circuits be bad and not letting the batteries get a full charge? Does removing the circuits make a difference?

 

[WalkIntoTheLight]

Removing a protection circuit shouldn't make a difference to the voltage or capacity. At least, not a noticeable difference.

It sounds like your capacity measurements are in the right ballpark for those cells. Did the capacity drop after removing the protection? Perhaps you shorted or damaged the cell when removing it?

 

[Knife Collector]

What dropped was the voltage. The ones with circuits still showed 4.2, but the one I removed the circuits showed around 3.7 on my meter.
I wanted to to charge them more, but without the circuits, I was afraid to since they showed full charge before I took the circuits off.
Not sure if the BT-3100 will notice a full charge on an unprotected cell and shut off.

 

[hiuintahs]

What dropped was the voltage. The ones with circuits still showed 4.2, but the one I removed the circuits showed around 3.7 on my meter.
I wanted to to charge them more, but without the circuits, I was afraid to since they showed full charge before I took the circuits off.
Not sure if the BT-3100 will notice a full charge on an unprotected cell and shut off.

Let me see if I can provide some insight. Chargers don't know the difference between a cell with a protection circuit and one without one. All they see is the voltage of the battery terminals. A protection circuit is in series with one of the terminals and they use Mosfets which are like semiconductor switches. So the voltage drop across the protection circuit is negligible. And you are right that the voltage of the battery shouldn't change much at all if any between having this protection circuit installed or having it off.

Something doesn't sound right. Perhaps the battery got shorted (discharged) somewhat in the process of removing the protection circuit. So I can see your concern for not wanting to put the cell back in a charger. But if you are measuring the voltage between the two terminals (neg end & pos end)...........then that is what the voltage is and somehow it got discharged. Can you post a picture of what the cell looks like after you finished removing all the protection circuitry stuff? Did you remove the skinny metal strip down the side of the cell? Did you re-wrap the cell?

I've taken a few protection circuits off and haven't had any issues. Take a look at these pictures. Did you do pretty much the same?
https://www.candlepowerforums.com/v...0mAh-18650-batteries-too-wide-now-retrofitted

So I'd put the cell in the charger and watch it. If the charger sees the voltage the same as you do at around 3.7v, then it will pump charge into it. If your charger has a display or voltage readout that will be helpful to watch things. You can also test the voltage of the battery with your multimeter while its being charged. It should read a tenth of a volt or so higher while being charged in the CC (constant current mode) until voltage reaches 4.20v and then it holds constant voltage (CV) while the current drops. Even an amp of charge current won't make the cell get much warmer or hot so I'd watch and touch to make sure things are not amiss.

 

[Knife Collector]

I put them back on the charger about an hour ago, the charger shows about 3.85 at the moment. They are not getting hot or even warm.
This happened to all 4 of the batteries I removed the circuit from, and all show about the same voltage. After the circuits were removed, and now.
I took the wrapper off holding the circuit and then removed the top, bottom and the side metal strip.
Here is a pic if it will come thru.

 

[hiuintahs]

OK. Let me know what happens. I'm thinking they just got discharged somehow. Kind of weird. But if they charge up to 4.20v without heat or any other issues, then I think you will be good to go.

 

[WalkIntoTheLight]

Yeah, that's really odd. One getting shorted would explain it. But all four? That doesn't seem likely.

BTW, when messing around with batteries such as removing protection circuits and stuff like that, it's probably better to mostly discharge the cell first. Of course, I don't follow my own advice, but that's just me being lazy about it.

 

[Knife Collector]

I just got home a bit ago, and started the charging again. One has just shut off at 4.20 volts, and the others are close behind. I am tempted to remove the circuit from another fully charged cell, just to see what happens.