View Full Version : DC motor controller

06-01-2022, 06:25 PM
We have a 600w 220vDC motor that we need to control from the breakout board. Is there a suitable motor controller available with a PWM or 0-10v input and an inhibitor switch? Everything I've seen doesn't have an inhibitor switch and it looks like the only way to turn the motor controller off and on via the breakout board is through a relay on the 240vAC supply. I tried a solid state relay on the DC output to the motor, although there are separate issues with solid state relays and it wasn't satisfactory.

We do have a great deal of experience with VFDs and AC setups already yet I'm not really willing to junk the DC motor, as it's fine for the job, and an AC setup would be another 250 expense that isn't really necessary. Information on DC setups seems to be a little thin on the net. How have other people addressed this issue?

06-01-2022, 08:38 PM
Most basic DC motor controllers do rely on switching the 240VAC supply, but there are controllers that do have internal enable circuitry.

Sprint drives (I've just checked the 680i manual) have a run input, but they have the following warning -

WARNING. RUN is an electronic
inhibit function. The field remains energised, and all power terminals ‘live’. RUN must not be relied
on to ensure the machine is stationary during hazardous operations. Remove the power source to the

Having had a quick look at a couple KB Electronics drives (KBIC and KBMM), they also have an inhibit input, but again they only disable the armature output, so the motor will still be live with voltage on the terminals.

Is there any reason why you can't use a relay as the main inhibit, as DC drives are designed to handle the input being switched regularly.

06-01-2022, 09:21 PM
OK, that answers the question about the Sprint motor driver and if it cuts power to the motor. The reason was just to make the install simpler as I suspect the on signal from this breakout board is only 5v, as it will run from a USB cable, so would need two relays, one 5V to 24V, and 24V to 240VAC. Although it would make adding a door or chuck guard interlock easier as it can switch the 24V loop. There is also a delay switching the power supply on, and then another delay spinning up the chuck, and it may have reduced that. And not wanting to keep switching it on and off although you say it's not an issue.

Thank you for your help. It's a big hand up knowing I was on the right path.

21-01-2022, 07:37 PM
Got a new question. Come to run a program and it sits waiting for the spindle speed to increase. I don't have a spindle encoder, and do not have an input for one selected in the LinuxCNC stepconf. The documentation says if there isn't one then LinuxCNC should just simulate it anyway yet it isn't. I can't see any options in the HAL configuration and can't work out how to add the simulate encoder option in. Can anyone help with this one?

21-01-2022, 08:12 PM
Probably best to ask on the LinuxCNC forum.

22-01-2022, 04:24 PM
Never mind. Got it worked out now. The machine is running and cutting metal.

Lee Roberts
22-01-2022, 06:30 PM
Never mind. Got it worked out now. The machine is running and cutting metal.

What was the fix/issue ?

23-01-2022, 11:12 AM
I'm not sure if this could be an issue for you but some drives from Sprint and KB are NOT isolated from mains, so you cannot make a ground connection from the BoB to the drive. It is possible to extend control to them but an isolator is needed.

23-01-2022, 03:36 PM
What was the fix/issue ?

I sorted out a pickup on the spindle for a speed input. It was after spending the day on it connecting everything and doing the wiring, I was just being belligerent about not doing any more. Came back to it the next day and just spent the 30 mins sorting it and it all works.