# High Amp DC Motor Controller

I have found a following gearbox + motor combination that fits the rpm and torque requirements needed. They are here:

The motor has a stall current of 85 amps. I am struggling to find a DC Motor Controller that can handle 85 amps at 12 volts running through it. This controller would have to be able to take in 0-5 logical volts to control motor speed, be able to have a 12v input from the battery to power the motors, and a terminal that outputs 0-12 volts proportional to the inputted 0-5 logical volts. It would have to be able to have at least 85 amps drawn through it (probably a little more than that for safety). Do you know of a place online where we can find such a device for less than \$100? The highest we have found was one for about \$60 dollars each (one per motor) and could only handle a constant 60 amps of current and a peak current of 100 amps for only up to 2 seconds. Because 85 amps is the stall current of the motors, this is unsafe as, if the motors were jammed up by something for more than 2 seconds, for instance, the controllers would burn out.

Thank you

P.S.

If we calculate that we need x torque to speed up to y rpm in the necessary time period, buying a motor with x rated torque and y rated rpm should be sufficient, as the torque below the rated rpm is greater than the rated torque on DC motors. Is this correct?

Edit: One idea is to have current limiting. Something to see that when the current could get over 50 amps or so, it would stay at or below 50 amps. What type of circuit could I buy/make to do this?

Most high performance motor controllers should have a current sense output voltage you can
sense to implement over-current protection. A suitable slowblow fuse can also protect from prolonged
overcurrent.

Torque depends on current, so starting from a standstill the acceleration will be that due to the stall
torque, but that torque will drop off as the motor speeds up and back-EMF starts to balance out the
supply voltage.

handle a constant 60 amps of current and a peak current of 100 amps for only up to 2 seconds.

That should work fine. The stall current is drawn only very briefly.

So, why would this motor controller limit the current, by default, to a current higher than it can handle? It says, by default, it limits current to 60 amps, but can only handle 22 amps.

Regardless, I can set the built in limit to 22 amps. So, with the motor above, if the current is limited to 22 amps, then, the torque will be forced at or below 1250 gcm, and the speed potential will be generally unaffected? The hope for me is that the motor could accelerate up to its rated speed at, or above, its rated torque. Is this possible if it is limited to 22 amps?

Thanks

PureStress:
So, why would this motor controller limit the current, by default, to a current higher than it can handle? It says, by default, it limits current to 60 amps, but can only handle 22 amps.

Regardless, I can set the built in limit to 22 amps. So, with the motor above, if the current is limited to 22 amps, then, the torque will be forced at or below 1250 gcm, and the speed potential will be generally unaffected? The hope for me is that the motor could accelerate up to its rated speed at, or above, its rated torque. Is this possible if it is limited to 22 amps?

Thanks

Please read the specs again! The 22 amps is continuous operation. The limit for instantaneous current is 60 amps.

Paul

Ok, so with the motor above, if the current is limited to 22 amps, then, the torque will be forced at or below 1250 gcm, and the speed potential will be generally unaffected? The hope for me is that the motor could accelerate up to its rated speed at, or above, its rated torque. Is this possible if it is limited to 22 amps?

Thanks

PureStress:
Ok, so with the motor above, if the current is limited to 22 amps, then, the torque will be forced at or below 1250 gcm, and the speed potential will be generally unaffected? The hope for me is that the motor could accelerate up to its rated speed at, or above, its rated torque. Is this possible if it is limited to 22 amps?

Thanks

All you wrote is true, however, the 60 amps will allow the motor to rapidly accelerate from a stop to it's maximum speed. By limiting the maximum amps to 22, you eliminate the rapid acceleration. Only testing will determine what the acceleration will be.

paul

Thank you. My worry with limiting it only to 60 amps, is that, say there was a malfunction and, say, the robot's chains jammed up, I would be worried that the 60 amps would be sent for longer than the controller can handle, and as such destroy it. Am I missing something here or is that a valid concern?

Am I missing something here

Could be, but do check the motor controller data sheet for the details. That is your very best source of reliable information.

PureStress:
I have found a following gearbox + motor combination that fits the rpm and torque requirements needed. They are here:

The motor has a stall current of 85 amps. I am struggling to find a DC Motor Controller that can handle 85 amps at 12 volts running through it. This controller would have to be able to take in 0-5 logical volts to control motor speed, be able to have a 12v input from the battery to power the motors, and a terminal that outputs 0-12 volts proportional to the inputted 0-5 logical volts. It would have to be able to have at least 85 amps drawn through it (probably a little more than that for safety). Do you know of a place online where we can find such a device for less than \$100? The highest we have found was one for about \$60 dollars each (one per motor) and could only handle a constant 60 amps of current and a peak current of 100 amps for only up to 2 seconds. Because 85 amps is the stall current of the motors, this is unsafe as, if the motors were jammed up by something for more than 2 seconds, for instance, the controllers would burn out.

Thank you

P.S.

If we calculate that we need x torque to speed up to y rpm in the necessary time period, buying a motor with x rated torque and y rated rpm should be sufficient, as the torque below the rated rpm is greater than the rated torque on DC motors. Is this correct?

Edit: One idea is to have current limiting. Something to see that when the current could get over 50 amps or so, it would stay at or below 50 amps. What type of circuit could I buy/make to do this?

must be one heck of a setup! I ran 2 power wheel chairs off of a 2x25 from these guys and it had no problem hauling my 220lbs around sitting on it.

https://www.dimensionengineering.com/ they offer a 2x60 that would do it but its more than 100... I highly recommend them.

I can see where you give the requirement for being able to adjust motor speed. I see NO requirement to reverse motor direction.

If speed is the only requirement, then use MOSFETs and no motor controller board.

Paul

PureStress:
Thank you. My worry with limiting it only to 60 amps, is that, say there was a malfunction and, say, the robot's chains jammed up, I would be worried that the 60 amps would be sent for longer than the controller can handle, and as such destroy it. Am I missing something here or is that a valid concern?

Very valid concern - which is why controllers with over-current detection that is configurable are great. The
simplest approach is find a current-limiting controller and set the current limit to a safe level.