Relay for DC motor

Hi, I am building a rover and I use high-power DC motors, whose current can be up to 30A @24V. I intend to use relays to turn it on and off (on & off buttons). I am wondering which relay can fit my need. I looked up some relays, but they are rated 20A@~230V or 50A@~230V. I use 24V batteries to power my rover. Can I use the one of 10A@~230V relay for my motor 30A@24V? Because I use DC source, not the AC 230V, I am confused.


Hi Minh,

Those are some powerful motors, can I ask why you want to drive them via relays instead of using a motor controller?
Granted a motor controller is more expensive but if you need control over the motor’s speed you will need a motor controller, or at least a motor driver. Switching the relays rapidly on and off may work for a time, but with a current that large you may find the relay contacts weld themselves closed if they are continuously switching in and out to try and control your rover’s speed.
I’ll include a link to the difference between drivers and controllers below.


Hi Trent, thanks for your reply. This is only the start/stop circuit. Because I want to use the virtual stop button from my remote controller to stop the rover, I implement a latching circuit which is a bit similar to latching in PLC. I do have a motor driver for each motor.


Hi Minh
Be careful with relays at those sort of currents. They are rated very differently for AC and DC. A relay rated for 20A AC may be only good for 10A DC. Both ratings are usually shown.

For the currents you are quoting you may have to look at contactors but the same applies here. I think they are rated differently also.The coils are different also. Some contactors operate with AC coils and if you use them with DC you finish up with smoke.

If building this from scratch I would tend to use schottky diodes across the relays instead of the 1N4??? series. The 1N4??? are pretty slow and may not catch the relay back EMF quickly enough.
Cheers Bob


Hi Minh,

Core doesn’t have any relays with a rating that high. You might need to look into relays or contactors from a more industrial supplier like Element 14 or RS components.

Bob makes a good point about checking the switched voltage type. The largest relay we have is a solid-state relay (SKU: COM-13015) which will only switch on the zero-crossing part of the load waveform, so it only works with an AC load.

Hi Trent

This appears to be a zero crossing AC load only unit. Unsuitable for this application.
Cheers Bob

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Hi Bob,

I mentioned that relay as an example of why you have to check the load type requirements, but reading it back I’ve worded it poorly and it sounds like a suggestion. I’ll edit and rephrase the post to avoid confusion for anyone skim-reading later.