### Author Topic: battery selection for a motor  (Read 566 times)

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#### MC

• Jr. Member
• Posts: 16
##### battery selection for a motor
« on: August 31, 2011, 05:22:00 AM »
Hi

i am bit confued over the battery selection for a  motor

if the battery of 1300Ah battery is what i require, and the machine needs a 260A current ,and should run for 5hours, how can i know if that the machine takes the current for entire hour or per hour or per min?

the motor takes 260Amps so does it mean that it will take total 260 Amps as long as it is on ? so 260Amps for 5 working hours or may be 260 Amps for 8 woking hours also?

thank you

• Jr. Member
• Posts: 14
##### Re: battery selection for a motor
« Reply #1 on: August 31, 2011, 06:38:38 AM »
Quote
how can i know if that the machine takes the current for entire hour or per hour or per min?
I am not sure what you're asking here.. But if your motor isn't running, it will not use current or a very small current for the motor controller.

1300 Ah means that the battery has enough charge to supply 1300 A during 1 hour (those are huge numbers by the way! You sure it's a 1300 Ah battery?). However, because of the  internal resistance of the battery, it probably can't do that.

You are correct though, if you divide the capacity by the current used you get the hours the battery SHOULD last at that current. If that current is the maximum current used, but is only required a short amount of time your batteries should last longer.

Hope this helps..

#### MC

• Jr. Member
• Posts: 16
##### Re: battery selection for a motor
« Reply #2 on: August 31, 2011, 07:07:13 AM »
Hi
what i mean to say is that if the motor has a current rating of 260Amps
so now if the motor runs on full capacity and has a battery for eg of 1300AH then the battery will last for 5 hours by cal
but now if the motor runs at full speed for 30 min and then slowly but not stopped for the rest of the 30 min so how do we know that in the first 30 min it took how much current and then next 30 min because it went slow it took less Amps ?

#### Soeren

• Supreme Robot
• Posts: 4,672
##### Re: battery selection for a motor
« Reply #3 on: August 31, 2011, 10:54:19 AM »
Hi,

what i mean to say is that if the motor has a current rating of 260Amps
so now if the motor runs on full capacity and has a battery for eg of 1300AH then the battery will last for 5 hours by cal
It won't.
The capacity of large batteries is specified as the C20, which for a 1300Ah battery means that (new battery of course) it can supply 1300/20 = 65A for 20 hours. Any higher current draw and the nominal capacity goes down.

but now if the motor runs at full speed for 30 min and then slowly but not stopped for the rest of the 30 min so how do we know that in the first 30 min it took how much current and then next 30 min because it went slow it took less Amps ?
Look into power management circuits like used on eg. laptop PC's.
You simply (or not so simply) measure how much current is drawn in each time unit (say 1/10 second). This can be done with a microcontroller or by dedicated chips. Another solution is to integrate with a large but leak proof capacitor.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?