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redgiki
09-24-2005, 08:33 PM
I recently purchased two 3S1P 2100mAh 12C Dymond LiPo batteries. They were a good deal at $45 each.

My question is this: my charger defaults to only 1 amp charging rate for this 3S pack. What is the generally-accepted maximum charge rate on a LiPo pack? I've heard "1C" as a common rate, meaning the amp-hour rating of the battery. So a 2100mAh battery could be charged safely at 2.1 Amps then, right?

At 1 amp, full charge time is nearly two hours. This is OK for overnight charging prior to flying, but not so great for the weekend of flying I'm planning next week!

I'm charging a pack at 2 amps right now, checking every 5 minutes to see if it's getting warm, with a Triton heat sensor attached set to turn off charging if the pack reaches 130 degrees farenheit. I'd love to know what the "real" guidelines are though... 0.5A per cell sure seems low.

Maybe I should just go buy four or five more LiPos to keep me in the air... $$$$$....

--
Matt B.

Twmaster
09-24-2005, 09:05 PM
Yes you are correct 1C or 1 x the pack rating is the maximum safe charge rate. Good idea to use that temp probe too.

I always have several packs when I go to the Aerodrome for the day.

Greg Covey
09-25-2005, 01:27 AM
Matt,

Always use a 1C charge rate for Lithium cells with the exception of Skyvolt cells from FMA that can be charged at a 3C rate with the Skyvolt charger for a 20 minute charge time.

Matt Kirsch
09-25-2005, 01:33 AM
Normally, a 1C charge will take 45 minutes to an hour if you don't fly until the motor cuts out. Unfortunately for the impatient, 1C is the best you can do with conventional LiPolys.

timocharis
09-25-2005, 06:58 AM
I generally keep it to .8C (roughly) just to be careful. I get very good mileage from my packs, so maybe there's something to it.

If you're not balancing, it's also a fairly good idea to pull the packs a little early to avoid overcharging the "high" cell. But in practice this doesn't seem to matter much.


Dave

redgiki
09-25-2005, 08:17 PM
Matt,
...Skyvolt cells from FMA that can be charged at a 3C...
Greg,

Thanks for the plug :) I was wondering why Kokam/Skyvolt systems were more expensive than others.

Am I correct in assuming that the Skyvolt system can charge faster, basically, because it has better cell temperature monitoring?

At the size of packs I'm using (3S, 2100mAh) I'm not horribly concerned about pack life expectancy. I mean, $45 is two gallons of nitro fuel :) But I am concerned about my plans for my next electric, which will be a .60-sized bird, with commensurately larger, more expensive packs.

What is it about the Skyvolt system that makes it a better choice for big birds vs generic LiPo pack assemblies?

Greg Covey
09-25-2005, 11:47 PM
The combination of the cell balancing charger and the Kokam SHD cells allow for a 3C charge rate. What makes the Skyvolt system unique is that the cells are individually monitored on both charge and discharge cycles. Therefor, as long as the user doesn't severly over-current the cell or reach pack temperatures higher than 160 degrees F, you are pretty much guaranteed 200-500 cycles before losing more than 10% capacity. The Skyvolt packs come with on-shot temperature dots for 160 and 180 degrees F used for warrenty as well as a re0usable temperature strip to monitor pack temperature and make air cooling changes, if needed. For big packs, you pay big money, so you might as well protect yourself from over charging or over discharging.

falingtrea
09-27-2005, 05:37 PM
I found this doc on the web. Looks like a good FAQ on LiPo batteries.
http://www.dynamoelectrics.com/LiPo%20Essay.aspx

Bullwhip
09-27-2005, 10:03 PM
Redgiki,
130 degrees F is to high a temperature setting for LiPo batteries according to the Triton manual. The suggestion is ambient plus 10 degrees. NiCad and NiMh are higher at 115 degrees F.

Bullwhip