I would like to power my heated bed with an external power supply and still use the printer board to control the temp through a relay or SSR.
Will this still work with the PID turning a relay on and off?
PID tuning doesn’t mean binary on/off. So I guess it wouldn’t work.
Yes it will work. It is best to use SSR or power MOSFETs. Stay away from mechanical relays for PID since the on/off cycles can be too fast and wears out the relay.
If you’re simply using a higher-power or higher-voltage (24V, not 240V) supply, you can join the board’s and PSU’s ground lines. The bed will then be hooked up to the PSU’s positive rail and the board’ mosfet drain, which is usually labeled bed (-) or something like that.
Of course this requires your bed’s transistor being able to handle the load.
I was questioning to do this as i am adding a silicone heating bed and didn’t know if the Solidoodle 2 with a Printrboard could handle it.
If i use an ATX supply and connect the SSR to the blue ( i think blue ) on off wire then that should be OK?
I could use the ATX power on wire straight to the printers board, there is little current draw there.
Not sure if I understand your wiring description, but in essence, what I did, was take the wrote that were between your board and heated bed, disconnect from your bed, and connect to the input of your SSR (make site the SSR can take 12vdc input). Then connect the SSR output side inline between your new larger power source + lead and one side of the bed heater. Connect the other lead of your heated bed to the - terminal of your new power source.
There are millions of ways to connect but I believe this is the safest, but I’m definitely open for correction. I’m an ME that does electrical work a lot, so I know enough to be dangerous. Hope this helps
Oh, and the rain you don’t want to use mechanical relays is that the response time is too slow for pwm. It will end up getting stuck open or closed, which will be the equivalent of bang bang control while probably damaging the relay coil. SSRs are pretty cheap on eBay or amazon though
Thats what i had in mind, thanks for confirming this but then i got to thinking about the power on/off wire in the ATX power supply. If i connected that directly to the bed heat connection on the main board may be able to do away with the SSR as the power on/off wire only has minimal current draw. Less than the original heatbed anyway.
Don’t use a relay for the extruders, or if you have PID enabled for the bed temp.
If you have PIDBEDTEMP disabled the bed temp is only checked every BED_CHECK_INTERVAL (default 5000mS) and a normal relay is fine, I have used a cheap automotive headlamp relay for well over a year now.
@Wayne_Friedt I’d suggest sticking with an SSR. An atx power supply takes a while before it’s rails are energized, and if you use pwm you will destroy it. For bang bang control you might be fine though