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John D
08-25-2005, 07:06 AM
Hello

I have two 1250mah, 11.1v, 10c 3s1p lipos that are good for 12.5A continuous.

If I connect these two in parallel, can the 3s2p battery cope with my brushless setup that draws 21A max?

regards

John

SargentM
08-25-2005, 07:37 AM
Yes. You can charget them at 2100mA too. You will need to make sure that the packs are all at the same voltage BEFORE putting them in parallel, and it helps if they are both the same age. If I was going to do it I would buy the two packs at the same time, or alternativley buy a 3S2P pack already assembled.

ragbag
08-25-2005, 09:54 AM
Having a 3s2p is convenient at hookup time.

When it comes time to balance the cells it is nice to have two separate packs. IMHO it is easier with three cells.;)

By George

Unbalanced prop
08-26-2005, 07:07 PM
Most vendors like Tanic, TP, Maxamps amd Kokam at least have or can install taps on their 3S2P packs to enable easy balancing through a balancer or charging each cell seperately. I use a TP 205 balancer to balance Tanic, TP, Maxamps and Apogee 3S2P packs. I had to add taps to the apogee packs, but the balancer works fine on all the various brands of 3S2P packs. Gives me a little extra piece of mind. :cool:

Doug

John D
08-29-2005, 12:30 PM
Thanks for the replies.

Is it okay to parallel 2 batteries with different capacities.

For example, can I connect a 1700mah 3s1p 11.1v lipo with a 1050mah 3s1p 11.1v lipo to end up with a 2750mah 11.1v 3s2p lipo. A 2750mah lipo would give me excellent flight times, not too much weight, and for 10C rated batteries would easily cope with my max. current of 21A.

If the answer to the above is yes, can they also be charged in parallel, or should they be charged individually?

fdix
08-29-2005, 12:56 PM
The answer is no...
If you put packs in parallel they must have the same capacity! If this is not the case at a certain point one pack will be empty whilst the other will still be halve full. You will overdischarge the smaller pack and destroy it.

Unbalanced prop
08-29-2005, 01:51 PM
John D

I have charged different capacity packs in parallel many times with no problems. As an example, I have hooked a Kokam 3S 1500, a Polyquest 3S 1100 and a Tanic 3S 1550 in parallel. I charged them at the 3 cell setting and a charge rate of 4 amps. You MUST be sure the voltage is fairly close before hooking the packs in parallel. I try and make sure the packs are within .3 volts of each other.

As far as discharging, I have never done it, but people do with no problems. Here is a post to a parallel discharge with different capacity cells. No damage is done to the cells, because the discharge still cuts off at the LVC (3 volts per cell) before damage is done to the cells. Since they are hooked in parallel, the voltage is the same on all the packs hooked in parallel as they equalize themselves by being hooked in parallel.

http://www.rcgroups.com/forums/showthread.php?t=360273&highlight=parallel+packs+of+different+capacity+

fdix
08-29-2005, 02:23 PM
You do learn sometihng new every day... From what I had heard unless you discharged with very low current running two different packs in parallel was not at all a good idea, but form the graphs in the thread Unbalanced prop linked to it seems okay to do so if you don't demand extreme performance.

GeraldRosebery
09-06-2005, 12:01 AM
Thanks for the replies.

Is it okay to parallel 2 batteries with different capacities.

For example, can I connect a 1700mah 3s1p 11.1v lipo with a 1050mah 3s1p 11.1v lipo to end up with a 2750mah 11.1v 3s2p lipo. A 2750mah lipo would give me excellent flight times, not too much weight, and for 10C rated batteries would easily cope with my max. current of 21A.

If the answer to the above is yes, can they also be charged in parallel, or should they be charged individually?

NO NO NO never connect mismatched cells in parallel, not unless you want afire that is.

ragbag
09-06-2005, 11:20 PM
I agree with Gerald, why tempt fate?

But then I wear suspenders and a belt. You will never hear of my vehical catching on fire from charging. I do all my charging at the house under close supervision.

I carry enough packs to fly for the day, when they are gone it is usualy to hot to hang around anymore anyway.

I have taps on all of my packs that didn't come with. them
By George

John D
09-07-2005, 12:19 AM
Okay - I'm convinced - it might work but why risk it - will not hook up 2 batteries with different capacities.

I charge my lipos in my office on a desk directly opposite to where I sit. That way I only need to glance up every now and then to see whats going on.

Thanks for the comments.

Unbalanced prop
09-07-2005, 05:21 AM
You will never hear of my vehical catching on fire from charging. I do all my charging at the house under close supervision.

I would NEVER charge in my vehicle either. :eek: When I go flying it is usually for several hours, so I charge at the field. I have a 12 volt marine type deep discharge battery that I setup at the field and run three chargers off the battery (2 AF 109s and a GP four port). What could be safer? Charging outside with no combustibles close. If something goes wrong inside, you better have a way to get the pack outside in a hurry or a bag of sand close by to dump on it. I also have taps on all my packs and a balancer (TP 205) that will work on all of them, with an adapter. Correctly balanced packs will perform better and last longer then non balanced ones. IMHO

Doug