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LiIon, LiPo, NiCd & NiMh General General Battery Support


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Old 03-19-2011, 05:02 PM   #1 (permalink)
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Default 3S Lipos at 4.21v per cell.... safe ??

Hi all,
I'm using an Imax B5 balancing charger to charge my 3S 11.1v 1100mah Lipos for my Blade SR.

All seems well, and the batteries perform great. But just out of interest, I dropped my DVM onto the contacts after the batteries were fully charged, and noticed that some of the cells are sitting at 4.21v (but also some sitting at 4.20v) (One 3S pack had overall voltage, fully charged, of 12.63v)

I've heard thet anything over 4.20v is dangerous, so should I be worried about 4.21v per cell or is that ok ????

Thanks in advance for any advice guys !!

Cheers, Pete
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Old 03-19-2011, 05:11 PM   #2 (permalink)
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Quote:
Originally Posted by CyclicPete View Post
Hi all,
I'm using an Imax B5 balancing charger to charge my 3S 11.1v 1100mah Lipos for my Blade SR.

All seems well, and the batteries perform great. But just out of interest, I dropped my DVM onto the contacts after the batteries were fully charged, and noticed that some of the cells are sitting at 4.21v (but also some sitting at 4.20v) (One 3S pack had overall voltage, fully charged, of 12.63v)

I've heard thet anything over 4.20v is dangerous, so should I be worried about 4.21v per cell or is that ok ????

Thanks in advance for any advice guys !!

Cheers, Pete
Most multimeters are not accurate to .01V, so keep that in mind. But no, there is not problem with the cells at 4.21V even if they are really at that voltage.
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Old 03-19-2011, 06:52 PM   #3 (permalink)
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Thanks, that is quite re-assuring !

I've also noticed that if I stop charging when my charger reads 3.9v per cell , then measure with my DVM , my DVM says 3.8v per cell ???

On the whole my charger seems to be telling me there is approx 0.1v extra per cell , than my DVM tells me !!

I don't know which one to believe !!!!
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Old 03-19-2011, 09:02 PM   #4 (permalink)
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Remember that when current is flowing into a pack, it places a charge load on it and that will raise the voltage. When the load is removed, the voltage will settle some. That is likely what you are seeing there.
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Old 03-20-2011, 08:17 AM   #5 (permalink)
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Quote:
Originally Posted by CyclicPete View Post
Thanks, that is quite re-assuring !

I've also noticed that if I stop charging when my charger reads 3.9v per cell , then measure with my DVM , my DVM says 3.8v per cell ???

On the whole my charger seems to be telling me there is approx 0.1v extra per cell , than my DVM tells me !!

I don't know which one to believe !!!!

Confusus say: "Man with one DMM always know the voltage, Man with two DMM never know the voltage".
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Old 03-20-2011, 03:20 PM   #6 (permalink)
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Confusus say: "Man with one DMM always know the voltage, Man with two DMM never know the voltage".
I like that !!!!! Very true !!

I didn't know about the "charge load" raising the voltage. You learn something every day !! Especially on Helifreak !!

That would explain a few things though !!

So how far above 4.2v (per cell) for a Lipo is considered dangerous ???

4.22v ?....... 4.23v ?....... 4.24v ? ............... ??

(Is my fully charged 3s pack at 12.64v dangerous ????)
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Old 03-20-2011, 03:24 PM   #7 (permalink)
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Sorry ... double post
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Old 03-20-2011, 05:41 PM   #8 (permalink)
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There is no real "danger" voltage. At some point the pack starts to become damaged but I suspect it is nearer to 4.3V than 4.2V. I have personally seen lipos at 4.7V per cell while being charged at a high charge rate and they weren't even warm. It did trash the lipos though. Dude only got like 10-20 cycles out of the Volts 35C packs and they were gone.
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Old 03-20-2011, 08:27 PM   #9 (permalink)
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There is no real "danger" voltage. At some point the pack starts to become damaged but I suspect it is nearer to 4.3V than 4.2V. I have personally seen lipos at 4.7V per cell while being charged at a high charge rate and they weren't even warm. It did trash the lipos though. Dude only got like 10-20 cycles out of the Volts 35C packs and they were gone.
What amount of C are you charging at ??? for the lipos to die that quick you must me overcharging. 1C for every 1000mah would be the best. Mine are rated a 2C but i only do that if im in a rush, but thats the cost. fast=loss of batt life.
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Old 03-21-2011, 09:17 AM   #10 (permalink)
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I don't really understand the "C" thing with charging. The batts are 3S, 1100mah, and I'm charging them at 1.1amps. Is that 1 C ??
The batts perform great, I was Just a bit worried about them being slightlyover the 4.2v per cell which I've heard is a maximum.
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Old 03-21-2011, 01:04 PM   #11 (permalink)
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Yes "C" refers to the capacity in "Amp hours" and in your case is 1.1 (1100mAh = 1.1A)

So if your continuous discharge rating is say 30C that would equal 33 amps.
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Old 03-21-2011, 05:27 PM   #12 (permalink)
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Aha !! I see ! (Or should that be ... I "C" !!!)

Again, that makes sense ! I learn something every night from this forum !

Cheers All !!
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Old 03-22-2011, 03:06 AM   #13 (permalink)
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It surely will shorten life span of the lipos by overcharge or overdischarge
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Old 03-22-2011, 09:19 AM   #14 (permalink)
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Is 1C a safe charge rate for My lipo then ?
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Old 03-22-2011, 04:39 PM   #15 (permalink)
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Yes, 1C is the default rate for all LiPos I have ever used. Higher rates would be specified by the mfg.
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