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I have a project that has 14 DC motors, 8 of them have 6A nominal current the rest requires 5A. I'm thinking of using 12 LiPo batteries each 5000mAh, 30C~40C, connected in parallel so that total I'd have 60A.

My question is, can the batteries handle all of these motors? I'd like them to run at least 1 hour without any problem. Do you have any suggestions?

Thanks!

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  • \$\begingroup\$ More information needed, please. What voltage are the motors? LiPo batteries range from 4.2V charged to ~3.0V flat. Is there a W.h (Watt.hour) rating for the LiPo's you're proposing to use? Do you have a datasheet for them you can share with us? Putting all those batteries in parallel likely won't be a viable option; perhaps dedicate 1 LiPo to each motor instead, but lets get the basic info first :) \$\endgroup\$
    – Techydude
    Apr 29, 2015 at 12:05
  • \$\begingroup\$ All of the motors use 12V, 8 of them are 150Watt and the LiPo is 14.8V. The data sheet for the lipos: hobbyking.com/hobbyking/store/… \$\endgroup\$ Apr 29, 2015 at 12:12

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ok, so each battery has 4 cells in series, so you'll get 16.8V (fully charged) down to around 12.0V (flat), hence 14.8 "nominal". (Never ever discharge Li cells below ~3.0V/cell, or premature cell death is guaranteed).

they're 5000mAH capacity, and they're rated for ridiculously high discharge rates (at 5Amps, your discharge rate is 1C, not the 30-40C they're capable of), which means that you should be able to draw 5000mA (aka 5.0 Amps) for about 1 hour. so, you're OK there.

but, you almost certainly don't want to be putting all those batteries together in parallel to get "one big battery". all cells are different, especially as they age, & multiple cells in series (4 in this case) only makes this reality worse. Sure, you can short the batteries all together in parallel and they'll equalise each other out until they're all at the same voltage & no more current flowing between them, BUT: (a) performance is influenced downwards to the 'lowest common denominator' (i.e. the weakest battery); (b) a failure in 1 battery will bring down the whole system, and with that many in parallel, there's a huge amount of power behind the good ones to really wreak havoc on the failing/dead one, catastrophically so (as in fire, death, pesilence, etc); (c) power loss in conductors is proportional to the current squared (P = V.I = I².R), so by concentrating current unnecessarily, you're actually wasting some power you don't need to. I'd go for a distributed approach, 1 battery per motor.

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If the motors run continuously, with no changing load, and actually draw the rated power, and if the batteries actually retain and deliver as much power as they specify, and ignoring other effects and losses, then:

8 motors * 6A/hr = 48A/h

6 motors * 5A/hr = 30A/h

48 + 30 = 78A/h

Adding 15% for losses and safety margin,

(78 * .15) + 78 = 89.7A/h

If you used a 60A/h battery array on an 89.7A/h load, you could expect 60 / 89.7 = 0.6689 hours of operation.

If the motors were only "on" half of the time, then 2 / 89.7 = 44.85A/h, 60 / 44.85 = 1.34 hours.

Paralleling and charging multiple LiPo packs can be problematic. The better packs include a second connector for charging, which allows each cell to be individually charged. Any bank of LiPo's must be charged per-cell for safety. Some sort of power distribution, regulation, monitoring, and per-cell charging system likely needs engineered. LiPo's are very touchy about going over and under cell voltages and working in cold temperatures also.

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