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Solid state relay wiring

Hi, I have some of these SSR laying around


These are 5V high-level trigger relay with a working current of 3.8mA and 250V\2A capable load. I'd like to use with a 250V\35W air compressor that should work.

Are these type of SSR good for MG3? If yes, how should I wire it? MG3 has 2 connectors for controlling SSR (GND and +5V I think) while these type has 3 connectors (GND, +5V and Signal trigger).


Thank you

Hi Stefano,

Yes, for that very small sized fan 'compressor' it should be ok to switch it directly from an SSR.

A general comment about compressors: larger size compressors should not be operated by SSR. The SSR should drive a solenoid air valve instead.

But even with your small fan/compressor, you should find out what 'duty cycle' is allowed. This means how long it can be on for continuously, and how long a break is required. You then have to ensure that you don't operate it for too long, otherwise it may overheat or other problems.

For your SSR, you can connect the 5V to the K40 power supply 5V terminal, and the GND and Signal to the MG3 controller. Another customer is trying this in the next week or so, if you want you can hear how he goes before you try yourself.



Thanks.. this morning I have some spare time so I tried.

Connected my SSR like this:

  • 5v to 5v output on power supply
  • gnd to mg3 j2 - pin 2 (gnd)
  • trigger to mg3 j2 - pin 1 (air assist)

After powering up the system, I tested it and found 5v on 'trigger' just upon start (and of course this causes the relay to close).. I think it should be 0v until air assist is invoked by software. Led 2 on mg3 is off.

Sending M7 command via console causes the Led 2 to light up, testing the SSR there is 0v on trigger and the relay is now open. It seems that it is working in inverted mode, but parameter $95 is 0 (should be 0= normal operation and 1=inverted).

Should I simply set $95 to 1 and be safe?

Sure, invert the signal to match your SSR. The webpage you provided has both LOW and HIGH triggered SSR versions. I guess for whatever version you have the LOW triggered version, that's absolutely fine, just set $95=1



Thanks Dan,

actually I think my SSR is an HIGH triggered version, since it opens with 5v on trigger. The strange thing is that MG3 is outputting 5 V on 'air assist' pin when air assist is OFF (LED 2 is off). Just after starting all up there are 5 volts on MG3 air assist pin...


ok, well try $95=1 and let us know if you're happy with the result

Inverting it works, now with M7 relay closes and with M9 it opens.

But when trying a cut, air assist won't start; in Lightburn I checked the 'air assist' switch near the layer I want to cut but nothing happens. I should probably ask this in Lightburn forum..


Edit: nevermind, I found the option to switch between M8 and M7 in machine settings 🙂

Thank you!

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