Hey folks, I have a omtech Polar that I’d like to swap the air assist out on (built in fan is very loud)
I have a 24v lasertree air pump to swap in. Is there any reason I can’t simply wire this to a +24v and the wind poles on the 6442s controller to switch it on and off?
The pump probably requires much more current than the 500 mA limit mentioned in the 6442 manual, so a direct connection will eventually destroy the transistor inside the controller.
Instead, use a DC-DC solid state relay to protect the controller:
They come in two versions, AC and DC output; you want the DC flavor.
You can safely assume all cheap SSRs are essentially identical counterfeit / knockoffs, but avoid sellers with storefronts featuring beachware and dog collars.
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cheers, I knew there was probably something I was missing. I’ve previously wired in (on a different machine) an air assist that included a finder relay which needed a flyback diode across the poles to protect the controller, do you happen to know if that would be required with one of these? possibly a silly question but why DC/DC rather than AC on the Load side?
That’s needed for Old School mechanical relays with coils generating a magnetic field to move the armature. When the controller switches the relay off, the energy stored in the magnetic field must go somewhere, so the flyback diode routes it through the coil, rather than the controller.
SSRs have a transistor on the input: no magnetic field, no stored energy, no need for a flyback diode.
SSRs with an AC output have a triac controlling the output, so the current must pass through zero to turn it off. Because the voltage is AC, the output doesn’t have a polarity: connect either wire to either terminal.
SSRs with a DC output have a MOSFET that can switch off without a zero crossing. Even though the voltage is DC, the output may or may not be polarized: pay attention to the SSR label!
You mentioned a “24v lasertree air pump” which is almost certainly has a DC motor, so it needs a DC SSR.
In either case, the input will be polarized, so pay attention to those markings.
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excellent, thanks for the explanation, you’re quite right it does have an DC motor.
Here’s a pretty good video on why you need a snub diode with a coil.
I use these also for my exhaust fan, and previously my small compressor, on my Ruida.
@ednisley good call, that air pump draws about 950mA 
It’s a wonder how long that poor little transistor could last … 