Hi everybody, just a question to confirm what I’m thinking on this one. I was charging an 18500 Li-ion 1800mAh capacity protected cell from TrustFire and it got quite warm, they usually always stay cool during charging. This cell needs to be disposed of, right? I was using a cottonpickers USB charger with voltage monitor at 700mA when it got hot.
I have a pair of them that I have in a light my 5 year old son uses. Already got a new pair, this time AW’s from Lighthound…also protected 18500’s but with 1500mAh capacity. Being as how it’s in my son’s light, any question at all as to the cells integrity and it’s outta here.
Just checking in that this is the correct approach.
I only have 2 10440s from Ultrafire that aren’t “name brands” after this, everything else is Panasonic, AW or Redilast.
Thanks for input on this, never had one heat up before but I’ve not been into these kind of lights for very long either. My first Li-ions were purchased for a MagLite mod, a one cell from JayRob that I’ve had about a year, with my first cells being from Novae…32650 protected at 5500mAh. I have 6 of those and they’re all doing well.
Yeah, that definitely isn't supposed to happen. It could come from two man things. 1st, if the cell is an extremely low capacity and the charge current is to high (unlikely in this case) or 2nd if the internal resistance of the cell is to high. From the sounds of it it is option 2, which will only get worse as more time passes. It also means that it is not going to supply as much power when used in a flashlight.
The charger is working fine, charging other cells with no issue. The 18500 in question is 1800mAh capacity and was being charged at 700mA. So it wasn’t being charged at too high a rate.
The charge was in progress when I terminated it due to the heat issue. The voltage monitor was reporting something like 4.15 when I took it off the cell and it now shows 4.08.
Could it be that anyway? I mean, the charger is a USB charger so it could only pull some 1200mA from the USB port even if the charger went bad…being that it gets it power from the computer USB port it simply can’t provide enough total output to overcharge a 1800mA cell, can it?
At any rate, I’ve used the charger on another cell and it worked fine. Should I keep my eye on this charger to be on the safe side? I always charge the cells right here on the computer beside me and if I have to leave the computer I unplug it and restart it later rather than leave it.
How long was it between when you took it off the charger, and then measured that 4.08V?
I’m kind of thinking that you should check the voltage, maybe tomorrow, to see if it is maintaining the voltage.
You could also try measuring the current while it’s charging that 18500 also, i.e., set the charger to 700 mA charge rate and measure current to see if actually is charging 700 mA. I remember seeing page showing how to do that, by putting two pieces of aluminum foil with a piece of paper between them, then attach your meter (current mode/connection) leads to each of the aluminum pieces.
I don’t have an explanation for the warming up. Then again, I’m still a newbie (BTW, how long do I get to say that :)?)…
Edit: BTW, for a USB 2.0 port, maximum current is ~500 mA. Hmm. Maybe try setting your charge rate lower, to maybe 500 mA, and see if that battery still warms up when charging it?
From that much voltage drop in a short amount of time, I would say toss it. But the cell would have dropped some voltage right off the charger even if new. I suspect if you measure it in a day or two it will be even lower. Let it rest a day or two and measure again. Let us know what its voltage is then. But I do suspect its shot. As scaru already said, the internal resistance is probably what is causing the cell to build heat while charging.
Ok, so how do I check the charger input if it’s connected by magnets on leads? Are you saying to connect my DMM on either side of the positive contact in such a way that the input is running through my DMM? This would be with the DMM set to Amps?
The charger is a Cottonpickers charger, with built in digital voltmeter and 2 output selections…480mA and 700mA. I have another with 90mA and 200mA settings.
Edit: On 700 my DMM shows .53, on 480 it shows .39 This going into an NCR18650PD Panasonic cell
Hook the DMM up if it was another cell in series with the battery, set DMM to current. The current has to run through the DMM.
I really don’t think its the charger. The current readings above are perfectly acceptable.
My DMM has given me false readings when taking tail measurements in the past looking to see what amperage a light is pulling. I finally got readings that are close to what others get by using 12ga solid copper leads about 2 in long. I just set it up like that and took the magnet out of the alligator clip on the positive end of the charger, clipped it onto the red lead in the DMM with the the negtive magnetic alligator clip on the negative end of the battery. I held the black lead of the DMM to the positive side of the battery and plugged in the charger and got that .53 reading when the charger was set on 700mA.
So my DMM is off, or my computer is not allowing the charge to output more than 500mA or the charger is not functioning properly.
Was the battery almost discharged when you measured the current. If the battery voltage was high (almost fully charged) towards the end of the charge cycle the current would be lower when the charger hits the constant voltage stage.
Ah, forgot about that…no this cell had 4.05 when I put it on the charger and the charger was showing 4.14 going in. That might very well account for a lower amperage charge rate.
Thanks for reminding me. I’ll have to run something down before I can get that true reading.
As long as the voltage wasn’t 4.2v while charging, the charger shouldn’t have hit the constant voltage stage yet. At least my hobby charger doesn’t. The cottonpickers charger may be different.
Charger is just fine in the output dept, a 14500 cell with 840mAh capacity at rest @ 3.68V tested at the 700mA setting with the DMM showing .70, with an alternating .69 and back to .70.
The “problem cell” is still sitting at 4.08V. That was Wednesday night late when this happened, and it’s still sitting at 4.08V The charger, however, is daid! I noticed the illumination indicating charge dimmed a few times during the charge cycle so I pulled it off the charger and checked magnetic leads on the cell I was charging. Pulled the lead connection from the charger and put it back, all seemed well. Even flicked the amperage selector switch a couple of times. The charger now does nada, zilch. The display works fine, but no charging lights no matter what I try.
I contacted Cottonpickers and he’s sending out a replacement, virtually no questions asked. (virtually because he asked my mailing address to send a replacement out to)
I was wondering if it could be fixed, but then, it’s embedded in epoxy.
So now I don’t know if the cell should be tossed or not. It did get pretty dang hot, uncomfortable to hold but not impossible to hold.
A good testimony for customer service at Cottonpickers though, he’s all over it!
I do not think that an 18500 Trustfire cell puts out 1800 mAh’s. The .fire cells are consistently overrated. Just another.fire battery issue. I see that you have figured out the charger troubles. You should be better off with the AW cells. And for the record, Cottonpicker is an excellent vendor to deal with.
