I have a question regarding battery sizing and solar panel sizing ,I am not from an engineering background that's why i might need some help with this.

I want to run a 24vdc gear motor 180W 11.5 amps just for 20 mins everyday.The motor spins an 80 kgs drum.

1)What battery size should i get? ( watts amps and volts), Also what type of battery should i get eg: li-on ,deep cycle etc .

2)Also i need to charge this battery on solar, would a 50 W panel and a charge controller of 40 amps be fine? What controller should i get digital or analogue mppt or pwm.(i dont want it to be too complicated and expensive as this is just a university project

  • \$\begingroup\$ Let's start with the fact that if the motor is rated 180W and 24V, you will never run it at 11 amps. P = U * I , therefore 7.5Amp is your highest current you will ever run it at. \$\endgroup\$ Oct 2, 2018 at 10:54
  • \$\begingroup\$ so my battery should have how many amps? at a min? \$\endgroup\$ Oct 2, 2018 at 16:39

1 Answer 1


This sounds like a classic word problem where the trick is to know which 80% of the information to throw out.

The rest is contradictory. You say the load requires 24 V at 11.5 A. That comes out to 276 W. But then you specify 180 W. Huh? Which is it?

Let's say 11.5 A is the stall current, but 180 W is the running power. The startup will be short relative to the 20 minutes run time, so this comes down to needing to supply 24 V at (180 W)/(24 V) = 7.5 A for 20 minutes. The maximum current output needs to be at least 11.5 A.

The load requires 24 V, so that should be the battery voltage. 7.5 A for 20 minutes comes out to 2.5 Ah. Let's say you want the battery to run down to no less than half full, so you need at least a 5 Ah battery.

Two 12 V sealed lead-acid batteries of 5 Ah capacity or more would do fine. For simplicity, you could use two 12 V car batteries in series. You won't be able to find a car battery as small as 5 Ah, so any two of the same type of 12 V car batteries in series will do.

  • \$\begingroup\$ i dint know about the ohms law. thats what was said in the motor. \$\endgroup\$ Oct 2, 2018 at 16:38

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