1
\$\begingroup\$

Im dimensioning a quadcopter,and from my math, everything will draw a maximum load of 58-63 A. I need to choose Lipo batteries that can handle that current draw. From what I know: Max current: Capacity*C-Rating. For example, i cant use a 2200mAh 25C battery, because max current drawn will be 55A, but if I put 2 of those in parallel, I will maintain the 11.1V of 3S and will double the capacity. From that, my max current will be 4400*25=110A and I will be safe. Is my thinking right? Can I do this?

\$\endgroup\$
1
  • \$\begingroup\$ I will never need to draw 110A, the max current that i will need from the motors+eletronics will be 58-63A. With one battery(2200mAh 25C), i cant get that high, thats why im asking if its possible to put 2 in parallel to double max current drawn. \$\endgroup\$ Jan 25 '16 at 21:18
2
\$\begingroup\$

Yes, this can and is commonly done in the RC modelling crowd with lithium polymer batteries. Just make sure that both batteries are at the same state of charge (voltage within 50mV) before hooking them up, or you might damage the less charged one by charging it out of spec.
You can even use batteries of different capacities in parallel (but never in series!) as long as they have the same cell count and battery chemistry.

It is also possible to charge multiple batteries in parallel. Again, make sure that the batteries are not too mismatched in voltage before connecting, and make sure that you connect the balance plugs in parallel when balancing (which you should do on every charge).

Your maximum current estimate is correct, but keep in mind that cheap LiPos often overstate the maximum discharge rate somewhat.

\$\endgroup\$
3
  • \$\begingroup\$ Putting two complete packs in parallel while discharging requires all leads to be connected through the balancing connector as well. Just at charging doesn't ward off the problems like hardening or inversion upon discharge. Not to mention that, realistically you need a BMS in both cases to monitor all cells, rather than the stack voltage, since more than 1C will degrade batteries much, much less balanced than sub-1-C through micro stresses from factory to user and slight manufacturing unevenness. \$\endgroup\$
    – Asmyldof
    Jan 25 '16 at 22:23
  • \$\begingroup\$ I agree that it's safer and better for the batteries to parallel the individual cells in the packs even when discharging, but it's not strictly necessary unless you are building a commercial product. RC batteries have matched cells, and discharging fully is avoided. Nobody uses a BMS in RC models. \$\endgroup\$
    – jms
    Jan 25 '16 at 22:29
  • \$\begingroup\$ There's one more thing to consider, and that's what happens when a cell goes bad. If you have one good cell in parallel with one bad cell (maybe it's gone short-circuit for some reason), then you also kill the good cell in rather short order, and possibly the wiring as well. If you're okay with losing the entire composite pack if something goes wrong, then you're probably good, but keep that in mind. It might be better to put the two 3S packs in series or use a single 6S pack, with a system designed for the higher voltage. (less current for the same power too) \$\endgroup\$
    – AaronD
    Dec 29 '16 at 23:04

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.