I am using an ssr to control a linear compressor for a berd-air part cooling system.

Standard pwm signal did not vary the compressor output (it only operated at full) so I added a full bridge rectifier after the ssr so now one dc pulse = one pulse of the compressor. I use the M950 Q command to vary the frequency of my compressor and then adjust pwm duty cycle to get the pump running smoothly anywhere from 1-60hz.
The problem is that it takes a lot of gcode post processing to make my part cooling fan work.
The reason I want to use this compressor is so i can use one "fan" on a tool changing matching with a standard V6 hot end and with a super volcano hot end, even laser air assist some day.

I think people laser cutting or even cnc routers could use these compressors if fan outputs could be switched to pulse frequency modulation with some sort of duty cycle

@zapta Thanks alot. that did the trick.

the relay i'm using is here amazon relay

@mrehorstdmd that's kind of what I had in mind. My bed is not over powerd by any means so it takes a while to get up to temp. That gives the chamber some time to heat up and a 500x500 bed should help heat the enclosure too. I think I will try with the one heater for now and plug the machine into a watt meter to see if I have enough power left for a second heater if needed.

@mrehorstdmd thanks for the info!
mine is 153liters and has polycarbonate sheets on the sides and top. the bottom is 6.5mm aluminum that is mostly covered with insulation.
so two heaters it is. but I will probably blow a fuse if the bed and chamber are heating at the same time. might have to add a plug in the house and convert the machine from 110v to 220v.

i might double wall the sides and top or use something other than polycarbonate to enclose it.

my printer is massive and still vary much a work in progress.

I have a 400w 110v heater with an ssr. the heater has a 12v fan that that needs to be on with the heater so maybe i will switch to bang-bang and run the fan off of the dc side of the ssr.

my next problem is that my print bed is at the bottom of the machine so i might need to blow the hot air down. i'm planning to put fans in the enclosure at the top to blow the heat down the side not directly on the print and use thermostatic control for them when the top of the enclosure heats up.

and probably add a second heater because 400w probably wont be enough.

forgot to mention.
duet2 wifi with duex2 board running firmware 3.1.1

I am adding a enclosure heater to my printer.
i want to run a few fans at 100% to circulate the air and to blow over the heater element.

its probably a vary simple solution but i can find the answer.

i can't have a thermal controlled fan because the fan needs to turn on with the heater or the chamber will not heat up and the heating element will over heat without air flow.

i don't want an always on fan as i don't plan on using the chamber heater often.

the heater will be running pid so i can't hook the fan to the same output because i always want the fan at full power.

i just want to map a fan to come on full blast when the heater is running and to turn off at the end of the print.

I thought about having the slicer turn on a fan before heating the chamber but if i use the web interface to turn on the heater and forget about the fans i will over heat the element.

@zapta Thanks alot. that did the trick.

the relay i'm using is here amazon relay

@alankilian do you know what comand i need to enter into my config.g?

if i send M80 the relay turns on and the bed has power.
If i send m81 the relay shuts off and cuts the power to the bed, just what i want.

if i bypass the ssr then set;
"M143 H0 S40 ; set temperature limit for heater 0 to 40C" and send M80 when the bed passes 40 it sends a fault code but does not trigger m81 so the bed keeps getting hotter.
I assume i just need to add a line to the config but i cant find any information on it.

@alankilian one wire and 5 minutes later, my creation won't try to kill me as I sleep.

@alankilian thanks, that got the ball rolling!

@Chriss the only reason i want a fail safe is that an ssr will fail closed circuit. with two ssr its still possible to have two failures although highly unlikely its not 100% fail safe.
i currently have an Arduino relay thingy that I wanted to use as an on/off control, controlled by the duet but i cant just run the dc side in parallel with the dc side of the ssr because it won't function with the pwm signal. or maybe it will... the board for the relay has a bunch of other components on it. might try it anyway. if it doesn't work i think i will just put a simple reliable bimetal switch to cut the power if the bed gets higher than its rated for.

hooking up a separate Arduino is a little further than i want to go.