Help with battery

[CharlesVjr offline]

I am building a robot using 3 24v 3amp wheelchair motors one will need to run full time for an accessory and the other 2 will drive the bot tank style I was wondering what would be a good choice of battery to power the whole rig it will weigh around 600-800 lbs

[MarcoP]

Hi

I think there are two main points you have to decide regarding the batteries:
Their maximum current output and capacity.

Assuming you have all 3 motors running that would be 9A current. However stall current for the motors (what it draws when starting from a stopped position) is much higher.
So if you want good acceleration you will need much higher current batteries.

Regarding capacity, it also depends on the use. How long do you want the battery to last? Are you going to be running it at constant speeds or lot of speed changes?

Without knowing that data it's hard to recommend an adequate battery.

Rgds

[CharlesVjr offline]

I would need the batteries to last 3-4 hours and there will be a lot of speed and direction changes on the 2 drive motors but constant on the one accessories motor

[MarcoP]

To use a rule of thumb, you can assume constant 3A on accessory motor, and giving you want a lot of speed changes, i will assume average will be around 125% of nominal current for drive motors.

So it will be 4hours*(3A+2motors*3A*1,25) = 42Ah at 24V

You should be able to get two standard 12V (in series) or one 24V car lead battery with that capacity. But it will be heavy.

Lipo's would be a better option but you would probably have to use several in parallel which is a bit tricky...

Regards

[CharlesVjr offline]

So 2 65ah 12v lead acid batteries wired in series would be plenty to run the whole rig and also am not worried about the weight but thanks alot