Driving a large DC motor

I’m designing a pitching machine for a friend. I have two 24v 22.5A 400W(.5hp) DC motors (with a diode installed across the leads), and 2SK2529 MOSFETs rated for 60V/50A and high-speed switching, and a 24v 12Ah battery.
I’ve driven DC motors using arduino PWM and transistors before, but they were no where near as high a current load as these.
I’ve seen some DC speed controllers online and they seem far more complicated than the simple set-up I’m looking to use, although they probably include an H-bridge for direction control. But these big robust speed controllers make me think using a MOSFET and PWM are too simple.

So can I use these MOSFETs to drive these motors with PWM from an arduino? Or do I need to look at a more robust speed controller?

2SK2529.pdf (64 KB)

T12qS3FbNcXXXXXXXX_!!0-item_pic.jpg_400x400.jpg

Jrodenba: I'm designing a pitching machine for a friend. I have two 24v 22.5A 400W(.5hp) DC motors (with a diode installed across the leads), and 2SK2529 MOSFETs rated for 60V/50A and high-speed switching, and a 24v 12Ah battery. I've driven DC motors using arduino PWM and transistors before, but they were no where near as high a current load as these. I've seen some DC speed controllers online and they seem far more complicated than the simple set-up I'm looking to use, although they probably include an H-bridge for direction control. But these big robust speed controllers make me think using a MOSFET and PWM are too simple.

So can I use these MOSFETs to drive these motors with PWM from an arduino? Or do I need to look at a more robust speed controller?

At a minimum, I would drive the Gates to at least 10V, You want to turn on and off the MOSFET as fast as possible, Until it is fully on, its resistance is high.

There is a graph in the spec sheet that show the Drain Current vs Drain to Source Resistance with 4Vgs and 10Vgs. the Power loss for 4Vgs at 100A is 200W, for 10Vgs it is only 70W. Big difference.

Chuck.

At a minimum, I would drive the Gates to at least 10V, You want to turn on and off the MOSFET as fast as possible, Until it is fully on, its resistance is high.

There is a graph in the spec sheet that show the Drain Current vs Drain to Source Resistance with 4Vgs and 10Vgs. the Power loss for 4Vgs at 100A is 200W, for 10Vgs it is only 70W. Big difference.

Thanks for the reply!

So I might need to use PWM to drive something like a 2N2222 transitor that drives the gate of the MOSFET with between 10-20v? But the MOSFETs themselves shouldn't have any problems handling the load from the motors, right? They just look so small to be driving such high loads. Will I hit issues with switching speed when using one transistor to drive another?

Thanks again, Josh

I'd be very surprised if the battery held up with that load.

I'd be very surprised if the battery held up with that load.

It's a battery from an electric bike, and the motor specs are pretty close to the ones they use on the electric bikes here (China). And the motors themselves aren't actually driving a heavy load. So I'm not too worried.

Hi, Those pitching machines have wheels that exhibit quite a bit of inertia.

You may like to program in a maximum acceleration rate to the speed control, so if it is started from zero speed or some low speed and the pot is at full or suddenly turned to full, you will not get full 255 PWM.

This will probably cause an overload as the motor will take time and current to get up to speed. The expensive controllers have current limit built in to counter-act this problem.

You may even make it so if its turned ON and the pot is not at zero speed, the motor will not be driven until you turn the pot down.

Just some control thoughts.

Tom.... :)

You may like to program in a maximum acceleration rate to the speed control, so if it is started from zero speed or some low speed and the pot is at full or suddenly turned to full, you will not get full 255 PWM.

Thanks Tom!

I’m actually planning on implementing acceleration control in the code. I’m building a pair of IR tachometers, one for each wheel, that way I can use the RPM values to adjust speed and control acceleration. I’m hoping this will also allow for easier control over the pitches it throws; they should be able to preset the rotation speeds for curve balls, fast ball etc, and then just select the pitch they want from the LCD menu.
Josh