# A 12 Volt 60 Ah car battery for Motor Driver 18v25 CS

Hi,

for moving a 12 volt motor I was considering the Pololu High-Power Motor Driver 18v25 CS
I’d like to use a car battery (which is 12 Volts and 60 Ah).
Would this battery be dangerous for the motor driver cause of the 60 amperes?

thank you!

The number 60 Ah is the battery capacity in ampere-hours. It does not tell you how many amperes the battery is capable of supplying, rather it tells you approximately how long the battery will last if you draw a certain current. Example: 1 ampere for approximately 60 hours continuously.

Use Ohm’s law to determine how much current a circuit will draw.

Hello.

It sounds like you might not understand how current works. The motor driver will draw what current it needs from the battery. Batteries do not “push” current through the driver.

You should be able to use that battery with your Pololu High-Power Motor Driver 18v25 CS. Please note that if the motor’s current draw is more than the motor driver can source safely, you could still damage your motor driver.

-Derrill

Yes, I was thinking battery “push” rather than circuits draw from batteries…but…I must say that I was driven in error by a youtube video where the guy was selecting the motor controller in reason of the battery capacity rather than the motors…if I find it again, I’ll post a comment.

So, nothing is really needed between battery and motor controller or a fuse would be nice?

Do you know how much current the motor requires? It is important to check for the maximum value, known as the stall current, because the motor will draw that much if it is seriously loaded down. It also draws close to the stall current when it starts up, and can draw more than the stall current if it is rotating and the direction of rotation is suddenly reversed. You should not try to exceed the motor driver’s current rating.

If you can’t find out motor’s stall current rating, you can estimate it by measuring the motor resistance with a multimeter as you slowly rotate the motor shaft (unpowered, of course). Take the lowest value in ohms and divide that into the voltage of the motor power supply to get the stall current in amps.

Example: you measure 1 ohm, the power supply is 12 V, so the stall current will be about 12 amps.

Hi, I start wishing all of you an happy new year!

Thank you Jim Remington for the interesting tip: I took one of my motors, took the gearbox out (since it was too hard for me to rotate it manually, it is reduced to 12 rpm) and started measuring.

I must admit that the task it’s not that easy…values keep fluctuating while I manually rotate the shaft.
Anyway, I measure 11 ohms when the shaft is steady. The value goes up as soon as I rotate a little bit and release the shaft. Reaches 40 ohms drops to 20 and then again to 11.

Following your instructions and considering my motors are 12 V and using the 20ohms value…I would say the motor is 0,6 Amperes…does this make sense?

well…If there is some danger…I am considering buying two new motors, with all the specs

thanks!

Use the lowest value of the resistance, not a representative number, which suggests that the stall current of your motor is roughly 1 ampere. It is suitable for use with the 18V25 driver. In fact, the driver is serious overkill for this relatively low-power motor.

You should also measure the no-load current. Hook the motor up with your meter set on a current range, with the meter in series with one of the leads to a 12 volt power supply. You should find that the motor draws much less than 1 amp (100 mA might be expected), but this value will go up substantially when you grab the shaft.