FYI: I ran a 2S, 120mAh LiPo down to about 5.9V and my HiTec charger reported low voltage and refused to charge it. I configured the charger for NiMH and watched it charge back up to about 6.3V--took maybe 15 seconds. Re-configured to LiPo, 0.8C and it auto-charged to 8.4V, took about an hour. I ran it back down to about 75% of capacity and auto-charged again to full, took about 30 minutes.

Originally Posted by hoppy

12 min and 30% left would be around a 15 min flight if the whole capacity was used.

A 15 min flight is an average 4C draw.

I think you will still find them bad if you try to do a continuous 15C discharge - 30+A

Many "bad" packs can still be used for low current applications such as your parkflyer which in your test was averaging a ~9A draw.

By going bad, it's meant they are short on capacity and don't meet the original C rating.
But as to the 'apparent' miraculous recovery, that's a new one on me. Did you balance charge them the first time before the test?

Yes, I used a CellPro 4S to balance charge them to 12.6V and gave them a couple of minutes to make sure they were at room temperature before testing them. I could do more testing. For instance, I could monitor the current and just run them at FT in the tethered parkflyer and see how long they go before they cut out.
Thanks a lot.

Interesting experiment - was it cold the day you tested them? That really takes the oomph out of a pack.

Originally Posted by hoppy

Interesting experiment - was it cold the day you tested them? That really takes the oomph out of a pack.

I did it in a garage; I don't remember the temperature but it was comfortable, not too cold or hot.

So, I did the test I mentioned above (running the batts at full throttle in a parkflyer until cut out). Two of the batteries cut out shortly after three minutes, but the other two were still going at four minutes when I shut them down because they were getting too hot to hold. The average current for the two good ones (over the 4 minute period) was 19.5a and 19.63a (9.29C and 9.35C) and their remaining capacity was 40% and 44% (determined by maH restored during the charge cycle after the test). This morning I flew these two batteries in the parkflyer, and everything was fine for a 12 minute flight on each batt. I'm going to call these two OK but I'm not sure what I'm going to do with the two that only ran for 3 minutes.

Amazing. Good info for future reference.
I wonder what the IR on those packs is.

Originally Posted by hoppy

Amazing. Good info for future reference.
I wonder what the IR on those packs is.

I looked into estimating this but as I only have a DVM and a 100a shunt I don't think I can do it, because I can't accurately measure the voltage and current at the same time. It would be pretty easy to do if you have something like a WattMeter.

Hi Norm,
To make an IR meter you just need a known resistance and a volt meter. http://www.rcgroups.com/forums/showp...&postcount=272

I used 100W, 2 ohm resistors I got off the internet from China.

IR
Vu = unlaoded V
Vl = voltage under load

IR = (Vu - Vl) x R/Vl Don't forget to divide the answer by the number of cells in the pack.

The IR will probably not match other meters but, it can be used to effectively grade your own packs. Mine varied from 8 mohms to over a 100 mohms.

Originally Posted by hoppy

Hi Norm,
To make an IR meter you just need a known resistance and a volt meter. http://www.rcgroups.com/forums/showp...&postcount=272

I used 100W, 2 ohm resistors I got off the internet from China.

IR
Vu = unlaoded V
Vl = voltage under load

IR = (Vu - Vl) x R/Vl Don't forget to divide the answer by the number of cells in the pack.

The IR will probably not match other meters but, it can be used to effectively grade your own packs. Mine varied from 8 mohms to over a 100 mohms.

Oh, that's easy. I'm embarrassed to admit that I'm an electrical engineer and should have been able to figure this out myself

I read the post you referenced but I don't know anything at all about LiPo chemistry; do you know if it matters how much current you're pulling or if the IR changes as the cells heat up? I've got a 47ohm 5W load but that's not going to pull much current, so its probably not too good for this. Guess its time to pick up some power resistors.
Thanks a lot.
-norm

My tests at 10A and 20A showed little difference in the IR. My setup can give me either a 1 or 0.5 ohm load.
A 1 ohm resistor would yield a 12A load with a 3s pack. That would be 24C for a 500mah pack and a 3C load for a 4000mah pack. Using the 0.5 ohm load would increase that to 6C with the 4000mah pack.

The IR meter uses a 16A load. I assume the chargers with built in IR circuitry use less than a 5A load.

Good luck.

I do believe that battery manufacturers specification sheets state AC ohs as the ohms is measured using AC 1khz. There may be a slight difference by using DC ccts.

Hoppy and others, thanks for posting and maintaining all this information on LiPos, chargers and their care. For a newby like myself just getting into RC and specifically planes, remember that there is a lot to take in. Glow engines are not this complex!

I have been crazily reading stickies and boning up on my electrical math. The stickies on how to prevent a campfire while charging your LiPos was most enlightening (literally). These batteries are like nothing I have ever used, and their care and feeding have no similar counterpart with any other common battery type, and this may be the problem. To treat LiPos like you do other batteries might burn your house down.

I continue to madly read but not post just yet.

Thank you. Enjoy the hobby, it's a great time to be getting into electric flight.

Very helpful info. Have managed to salvage one battery so far and am about to resurrect some more.

Thank you all

hi. I have 3.7 battery that unlike other 1 cell batteries have 3 contacts. One is +, another is -, but can't understand what is 3rd one b/n them.

id pins.
used to identify the battery to the phone.
plug in the wrong battery and it won;t work