Air assist diode

I’m looking to put a dual air assist on my laser. It seems a relatively straightforward procedure will lots of good info on the forum and internet, but there is one bit Im struggling with. The consensus of opinion seems to be that it’s sensible to fit a diode but I can’t seem to find any info on what size diode I need.
I’m already slightly overwhelmed by the learning curve of using my laser without having to do a course in electronics to workout one component.

I believe you are inquiring about the circuit in the schematic ?
The electromagnet is the air assist/supply solenoid coil, the switch is the relay contacts where the relay coil (not shown) is picked by the CNC controller M8 or M7 output, the battery is your air solenoid DC power, typically 5VDC - 24VDC, it matches the air solenoid specs. The diode in this case shunts back EMF when the switch opens, protecting the switch contacts from arcing and from sending a voltage spike into the circuit on the other side of the switch, such as your CNC controller or other electronics. The diode in this case can be a common rectifier 1amp/1watt 1000Vrp , about $6 for a pack of 20 on amazon.
The silver band on one end of the diode (-) connects to the coil side of the circuit where battery positive (+) is applied.

Note that the relay mentioned above and picked by M8 or M7 is typically a small blue Arduino compatible unit and the boards they are mounted on have a back EMF diode for its coil, that protects the M8 or M7 output pin of the MCU. So there are 2 coils and 2 back EMF diodes in play here, but 1 is built into the relay package that replaces the switch in the schematic shown.


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Hi Lou,
Thank you for your help it’s very much appreciated.
I’m hooking up to a small compressor with a tank so that’ll fire up when the pressure drops, so I’m not connecting that to the laser electrically.
I’m taking the 24volt power from the ruida controller and using the wind and status connectors to work the solenoids. So I’ll probably put 3 diodes in, one at the controller end and one on each solenoid.
I’ve ordered my parts last night including a selection of diodes fortunately the ones you recommend are in the selection.

Thanks again for your help, you’ve saved a lot of head scratching,

Paul, to be honest, I don’t think the third shunt diode (at the controller) will buy you much. I think the ones across each solenoid coil will be sufficient. I went a slightly different route. I had a couple dual 24v digital relays ( laying around from a different project. They can be triggered with a high or low signal (I configured them for low). I hooked the Status and Wind connections from the controller to each of the trigger pins on the relay module, and then let the onboard relay do the work. This way the controller only has to deal with a very small amount of current that the electronics of the relay module requires instead of the coil on the solenoid. To be on the safe side, I still put the shunt diodes across the relay coils on the relay module. Just a thought.

Yes that is something else to consider.
Once again thank you very much for taking the time to help me out and your very clear and concise explanation.

If there is one at each end, how does it turn out 3 for 2 relays…?

This is what’s happening. You don’t need to be an electronics wiz to follow this video. He shows you on a scope what’s happening and why these are needed. It’s very enlightening to most people…

About 12:30 in, he shows the scope traces, if the other parts aren’t interesting to you.

Put the snub diodes in as close to the generator (coil) as practical.

I use 1N914 as they are cheap and plentiful…

Good luck


Thank you very much for taking the time to help me out.

Great video thanks