what current to charge at

[Mouse]

Hi there

first of all let me say that i am new to rc planes and the new batteries that are in use nowadays, (mainly used to ni-cads), but don,t know what rate to charge my li-po,s

I have just bought a ethos lxi4b pro charger and the instructions say to charge to the makers instructions but i have none, on the batterys it says 2250mha 3s1p 11.1v, 33c on one pack and 2400mha 11.1v, 20c on the other.

could someone help me with what some of these numbers mean, mainly the 33c and 20c and the 3s1p ones.

thank you

Bill.

[Martin Harris - Moderator]

Generally, LiPos should be charged at the C rate i.e. for yours, set the charger to 2250 mA (or nearest setting (down) on your charger) and 3S for the first pack and 2400 mA 3S on the other.

The 33C is the maximum discharge current (33 x C for a 2000 mAh pack would be 66 Amps)

A 3S 1P pack is 3 cells wired in series - the P refers to the number of series packs wired in parallel - rarely seen commercially supplied these days but for example a 4S 2P pack would be 8 cells giving the voltage from 4 cells with twice the capacity of each series pack. e.g. if the cells were 2000 mAh the pack would be a 14.8 V 4000 mAh one.

Many people run packs in parallel to increase the capacity without buying larger more expensive ones.

Edited By Martin Harris on 31/08/2013 22:50:41

[bren]

the way i would charge these would be

1. if i was at the field in a hurry i would charge them 2.2 amps and 2.4 amps as thats the max you can do

2. at home i would balance charge them both at 1 amp

[Pete B]

Assume that the charge rate on a Li-Po pack is 1C , unless otherwise stated - generally 5C maximum, Bill. The charge rate is very much different to the discharge rate, which are the C ratings you have quoted - 33C and 20C.

In the case of charging your Li-Po's , 1C is a charge rate of 2.25A in the first case, 2.4A for the second. If you have a 5C-rated pack for charging, you could charge at up to 5 x 2.25a = 11.25a for the first pack. The max charge rate is often not too obvious on a pack, so, as i said, unless you know for sure, stick to 1C.

Now the discharge rate - 33C means that theoretically you can discharge the pack without harm at 33 times its capacity, ie 33 x 2.25 = 74.25A. In practice most packs won't achieve this, or appreciate your attempts to attain it and will respond by getting very hot indeed or worse....

So take discharge rates with some salt and keep well within the rated capacity.

The Magnificent Timbo has explained it better than I ever can....

Pete

[Mouse]

Just a quick question while i try and get my head around all this.

is 2400 mAh the same as 2.4 amps and 2250 mAh the same as 2.25 amps.

I ask because the settings on my charger go from 0.1 A, to 4.0 A in .1 increments.

I also have some 1500 mAh 7.2v packs that i assume i could charge at 1.5 amps maximum. ????.

Thank you

Bill.

[bren]

thats how i see it mouse!! i never charge above the mah rate but it looks like i may be wrong on that one

2400 is mili amps i think

Edited By bren on 01/09/2013 12:01:22

[Pete B]

Yes, you're getting it, Bill.

I have a selection of 1C and 5C charge rate packs but, unless time is an issue - and it rarely is - I charge them all at 1C.

Pete

[Ben B]

2400mA = 2.4A

2400mAh means they could potentially supply 2400mA / 2.4A for one hour before being empty (it's a measure of capacity). So you set the charger for 2.4A and it should charge the batteries in an hour (it won't be exact because the pack won't hopefully be completely empty when you set it charging and the charge isn't maintained at 2.4A for the entire charge- most chargers reduce the ampage when you get near to trigger voltage).

Some batteries let you charge at higher currents (like the 5C mentioned) but it's kinder on the batteries which will subsequently last longer if you stick to 1C charges. Charging at the field usually requires quick charges but I try to avoid going over 2C (occasionally 3C if I'm in a hurry). Batteries with a high C rating tend to be more expensive so I tend to take more care of them!

If you do a balanced charge (which is always a good idea) you don't actually gain that much going from a 2C to, say, a 4C charge. Sure the intial charge is quickler but the bit which can take time is the balancing (depending on how out of balance the cells are). My experience is that as you go to higher and higher C rate charges you get a "law of diminishing returns" when you balance charge. And I wouldn't want to wallop 5C into a battery without balancing it.....

[Mouse]

So can i then assume that even though i have several packs all of 11.1 volts if the mAh is different i should charge at that rate, and also that the 1C rate will also change according to the mAh rating.

Bill.

sorry posted while other where writing.

Edited By Mouse on 01/09/2013 12:21:19

[Biggles' Elder Brother - Moderator]

Yes Bill that's correct. The voltage doesn't not influance the charging current - only the capacity in Amp or mAmps does that. But you must of course have your charger set for the correct voltage (number of cells) as that is used as part of the chargers method to know when the battery is full and so to stop charging.

BEB

[Mouse]

O.k I think I've got it.

one last thing though, if 1c of a 2250 mAh battery is a charge rate of 2.2 amps, is a charge rate of 2c 4.5 amps, i.e times 2 and the same for 3s ect, on the same mAh battery.

I think the 2c ect will not effect me as my charger is only rated to 4.0 amp maximum which i assume is another way of saying 40 w max as stated on the charger.

Thank you

Bill.

[Frank Skilbeck]

Posted by Mouse on 01/09/2013 16:21:40:

O.k I think I've got it.

one last thing though, if 1c of a 2250 mAh battery is a charge rate of 2.2 amps, is a charge rate of 2c 4.5 amps, i.e times 2 and the same for 3s ect, on the same mAh battery.

I think the 2c ect will not effect me as my charger is only rated to 4.0 amp maximum which i assume is another way of saying 40 w max as stated on the charger.

Thank you

Bill.

Yes that's it, but as others have noted it's kinder on the battery if you stick to less than 1C, there's not much benefit in going higher because once you reach the max voltage, 4·2v per cell the charger will start to reduce the current and the pack is fully charged when the amps have reduce to zero

[Mouse]

Hi all

Thank you all for your information and patience, and also for putting it in a way i could understand.

I now feel more confident about how to properly charge and look after my battery's in the future.

Until the next question.

Bill.