Running LiPo's in Parallel and Discharge Calculations

[nate80]

I';ve been looking around at batteries for the F550 rig I';m going to build.  Still waiting for a few parts to be delivered before I start but thought I';d look at what LiPo packs I might buy for it.

One of the primary reasons for my build is photography, so I';d like to get decent flight times of 16+ minutes.  I plan to run 2 LiPo batteries in parallel to help achieve this.

I understand that running 2 identical batteries in parallel means the Voltage remains the same as the Voltage of either of the individual packs, and that the total amps is simply the 2 LiPo';s output added together.

My two questions are, how is the Discharge rate calculated and am I better off running 3S or 4S batteries?

I was initially leaning toward 4S, but they are quite a bit heavier, and a 3S 5000mAh pack is significantly lighter than a 4S 5000mAh battery, so now I';m not sure.

And if I run 2 x (let';s say) 10C constant discharge (20C burst discharge) batteries in parallel does that mean the setup maintains 10C constant discharge (20C burst discharge), or is it increased to 20C constant discharge (40C burst discharge)?

Many thanks   

[rsmith21]

quote (And if I run 2 x (let';s say) 10C constant discharge (20C burst discharge) batteries in parallel does that mean the setup maintains 10C constant discharge (20C burst discharge), or is it increased to 20C constant discharge (40C burst discharge)?

end quote :)

The way I understand it is two packs in parallel, the voltage remains the same, but you have twice the amperage available and twice the flight time ( not quite true because you have the added weight of the additional cells)
So I think you are correct in saying if you wanted it you can draw 40C burst.

[nate80]

Thanks very much rsmith21, I appreciate the help.  With all respect, I';m not sure that';s quite right though.  The question of C ratings seems to be a question that gets asked quite a bit from my searches around the www.  Two good short answers I';ve stumbled across are:


The C rating does not change when in parallel, but the available amperage does double.


or:


Will two 1500mah 20C batteries in parallel be able to safely supply amps at twice the rate of a single 1500mah 20C battery.

The answer is YES.

Will two 1500mah 20C batteries in parallel be able to supply twice the current rate of a 3000mah 20C battery.

The answer is NO.

Both battery configurations mentioned above will supply at the same max C rate (20C). The max rating is that of any of the individual batteries.


Assuming that';s correct it looks like the maximum pull of my F550 hex with e305 20A ESC';s and e305 motors will be 120A.  So the 2 x 5000mAh 4S 10C batteries I was looking at might not be ok as 5 x 10 = 50 x 2 = 100A  That';s 20A less than the ratings of the ESCs and Motors.  The batteries do provide 20C burst, but I';m not sure if that means they are ok to run on my hex?

[guest325]

The thing to remember when you rate your batteries is that you very rarely fly at WOT so the burst current is more relevant. If you';re using it for AP  you should be ok with those batteries; I doubt that you will be running at 17A under normal circumstances.

[nate80]

Cheers Darrell.  What does ';WOT'; mean?

[guest325]

WOT = Wide Open Throttle

[nate80]

I';d not heard that before.  You learn something new every day. 

[Russ_H]

The C rating does not change, 20C remains 20C, but as you have doubled the available amp/hours available 20C now results in twice the available current.

[nate80]

The C rating does not change, 20C remains 20C, but as you have doubled the available amp/hours available 20C now results in twice the available current.

Nice, short and simple explanation.