View Full Version : Packs in Parallel and Series ... Please Set Me Straight!
jmb2232
02-07-2007, 02:49 PM
Here's a question for you battery guru's. Say I have two 3S, 2100mAh, 20C burst LiPo packs. What do I have when they are connected in 1)series and 2)parallel. I'll take a shot at it and correct me if I'm wrong.
1) 22.4V max; 2100mAh; and 20C burst
2) 11.2Vmax; 4200mAh; and 40C burst
Are any of these numbers correct? Thanks
Mike B.
z11355
02-07-2007, 02:55 PM
correct BUT I'm not convinced that you get 40C burst in reality. You are only drawing
1/2 the current so it's effectively the same though.
mudbogger2
02-07-2007, 06:05 PM
You still only get 20c its just the 4200mah 20c is 2x higher than 2100mah 20c.
2100 20c burst = 42 amps
4200 20c burst = 84 amps
jmb2232
02-07-2007, 09:09 PM
That doubling of the amperage was the basis for my question. So if you decide to parallel packs to increase flight time you have to be careful not to fry your ESC. The picture is a little clearer now. Thanks to both of you!
:thumbup:
Mike B.
Pinecone
02-09-2007, 05:30 AM
No the system will only draw as many amps as required for the voltage. SO if you take a Trex the flies fine on a 2100 pack at a max of 25 amps, and parallel 2 for longer flight times, it will still draw only 25 amps max.
Yes the pack will be able to supply more, but that doesn't mean the system will take more.
Efliernz
02-09-2007, 07:07 AM
No the system will only draw as many amps as required for the voltage. SO if you take a Trex the flies fine on a 2100 pack at a max of 25 amps, and parallel 2 for longer flight times, it will still draw only 25 amps max.
Spot on Terry. Current is what the motor wants to draw. Bigger blades/bigger motor, the more current it wants to draw. The more current "requested by the motor", the higher capacity/performance (C) battery required to be able to supply the current (amps) required.
The "Higher capacity" I refer to above means the abilty to deliver current. This may mean a 15C 2000mA pack delivering up to 30A or a 10C 3000mA pack that also can deliver 30A... both will be limited to 30A.
Pinecone
02-09-2007, 11:27 AM
Also don't forget that bad bearings can increase amp draw, as can bent parts.
That's why lipo alarms are a great idea.
jmb2232
02-09-2007, 01:26 PM
I understand, now. Thanks for all the replys! :cheers
Mike B.
P.S. Sorry for the double post above. I do not know how that happened. :dontknow
WillJames
02-09-2007, 08:44 PM
I got rid of the dup.
The other thing is that weight is not an electric flyers friend. Adding the weight of the parallel pack may get you the point of diminishing returns weight wise and increase the strain on the rest of the system.
You may want to consider going 4s from 3s instead of going up in p.