Max Charge Rate of Lithium Batteries

[Edge 540]

Ok, so we all know that lipos are a "charge at 1C" deal.

Why?
Where did the magic universal 1C limit come from? I realize a few chargers are capable of more,... but thats an exception to the rule.

Obviously the recommended rate is going to err on the side of caution as manufacturers (both hobby and industry) practice a little CYA. Whats the real threshold? Obviously its not as though a battery charged at 1.05C is going to instantly incinerate. Probably not at 1.2C either. What about 1.3... etc etc ?

How can R/C toys (those little airhogs etc) charge their lipos in 7-15 minutes? Are they really only depleting only 25% of the available capacity? I doubt it.

We found out earlier in the summer that we had mistakenly been charging a set of cheap Chinese lipos at 1.6C for weeks. These were very small foamy batteries. This represented dozens of cycles, many back to back on the same evening without any problems whatsoever.

Waiver: The over charging was done accidentally and obviously isn't recommended. I'm not suggesting trying this. I usually charge lipos at .5C unless its foamy batteries and we're in a hurry (at contest). Then its .9-1C MAX!

[pitviper51]

i use a Commen Sence RC balance charger with thier trex battery and i can charge it at 2 amps if i want, but the middle cell is a tad lazy so i charge at 1 most the time, sometimes even a trickle charge at .6 or lower( all day thing there) but i wouldnt do it with my other lipos that dont say max charge 2amp writen on it.

mike

[RichardK2046]

Charge at lower than 1C will not prolong battery life but anything over 1C pretty much depend on the pack.

The newer quality battery support 2C~3C charging, however, the 3C charging in lab does not show significant faster than the 2C due to CC CV algorithm, the optimal charging rate is 2C. A number of brand like TP, Flightpower, polyquest has claim to support 2C charging. I also saw a new brand cxarge on eBay also claim to support 2C charging but I haven't try it. I normally charge my pack in field at 2C and then 1C at home, so far shows no deterioration in pack life.

For other lower quality packs, I think it's the manufacturer try to give themselves more rooms not to damage the packs hence set a limit of 1C. I also found some 1800mAH pack, the manufacturer specify to charge at 1A.

[Edge 540]

The example that started this all was the $20 helicopter toy I was fixing for a cousin. How can they charge those things in 15 minutes? I'm jealous basically is all it come down to.

[superdh]

the little toy helis only have a very small 50-110mah single lipo cell, they are charging them at way more than 1c, probably closer to 4c but even at that the charge currents are very low and the cells seem to be able to survive it for awhile, however most of those batteries show a noticeable decrease in runtime after many charges, some go 20, some 100, but most show the decrease which indicates cell damage, if they took 1hr to charge they wouldn't sell as well!

[RichardK2046]

The only reason I can think of is this toy plane came with a 150mAH battery and the cheap charger that come with it has a fixed charge rate of say, 0.5A, force user to charge at 3C. LOL.

BTW, the charge rate depends on the battery pack and not the charger though some of the charger has to limited their charge current due to their output power. Like e-station BC6, their maximum power is 50W, they cannot go more than 2A to charge a 6S pack, if you have a 6S 5000mAH pack, it force the charge rate to 0.4C maximum though the battery pack can support 2C charging.

[SargeNZ]

You will find that the main reason packs 'die' is the cells go out of balance with one another - the result is that some cells are over charged, and others are over disharged, neither is good. The theory is that you can charge them at a higher rate, provided they are balance charged so they never go out of balance. The cheap toys that can charge in 15 minutes can do so because they are a single cell, so there is no possibility of the cells going out of balance.