View Full Version : Solid state relay for ON/OFF VFD

07-09-2017, 09:30 PM
Hi guys,

I am thinking of using this solid state relay to control the motor ON/OFF signal of the Chinese VFD. Also maybe to control the Enable on each of the servos.

RS part 720-3956

I use 24Vdc for the control side, and I've tried this SSR with a simple LED and it switches on/off fine.

My question is: this SSR is rated at a maximum 100mA for the load side and I have no idea what the load would be on the ON/OFF contacts of the VDF or for that matter the servo Enable, I suspect very low. Do you think this would work?

Consequently I suppose these signal contacts would be isolated from any VDF/driver return surge on disconnect and a diode on the load side may not be necessary?

Thanks for your advice.



07-09-2017, 09:37 PM
It's overkill but should work, the VFD should provide it's own trigger voltage and with that all you really need is some basic support components and a suitable transistor.
The maths and technology is very simple and the parts would probably cost pennies online, or less than a fiver from Maplin.

- Nick

07-09-2017, 09:45 PM
Thanks Nick,

This relay is quite cheap, around 6 and would just be connected straight to one of the opto outputs of my controller (they can drive up to 80V). I only chose it because it goes with my 24V limits circuit.


07-09-2017, 09:49 PM
If you have a common zero voltage reference it will work.