For my production printers, I just solder the heatbed wires directly to pcb, better safe then sorry 
@ThantiK How flat is that 1/8"? Went that route originally and couldn’t get a piece flat enough for my liking.
@John_Ridley , I shift my glass forward a little (or have it cut slightly short of 9") and tape it to the back center of the bed. You don’t want your thermistor falling off on a system like this.
@Matt_Miller that’s what the glass is for. Glass is manufactured flat.
@ThantiK yeah, never considered a broken thermistor… That’d be quite a hot source. I’m wondering if I could size a slow blow bus fuse to the ac mains so it blows if the city cycle implies malfunction… Would probably need to test iteratively. Good call
@Eric_Moy , better solution would be a 180C or so thermal fuse. Run your 12V through the thermal fuse, if the temp ever gets up that high, the alloy melts and disconnects the circuit.
You want a White-Rodgers 3L11-250 or equivalent. It’s a NC thermostat that opens @
124C and closes at 118C. If your thermistor ever fails or comes off the glass the bed will just chug along in this temp band until the print completes. You just need some DOW 736 adhesive to attach it to the underside of the silicone pad.
Awesome suggestion @Matt_Miller !
@Matt_Miller @ThantiK Great info guys, you all are going to kill my budget!
After killing a Mosfet or two by overheating them in a RAMPS, I stopped switching the heated bed directly with the mosfet and am using a relay instead. Works very well and rather cheap. Currrently I use the Teensylu I got from @Stephanie_A to run my Repstrap and have a RAMPS 1.4 for my Prusa i2 and my Wallace. IIRC the relay I am using cost 2 or 3€.
I could pick up an automotive relay real cheap, and even run the bed off a higher voltage. good idea @Robert_Koppl
If you’re not using an SSR make sure the relay has a protection diode, otherwise it could get stuck closed or cook stuff with the back EMF… or something like that
I’m referring to the coil of the solenoid, not the load. The relay is still DC actuated, and I’m thinking it is still affected
Yep, the coil of the solenoid can cause back-EMF and destroy stuff. You need a flyback diode to protect against this. It’s not hard to protect against. And good luck not being driven insane by the clicking noise constantly. Also forget PID tuning your bed or PWMing it.
Wow, $5 for a 25A relay…3-32vDC input, 250V switch…very nice.
@ThantiK yeah, I saw that one, then I saw a 40A for $5 more and said, why not?
I’ve got a board in my bonepile that has a blown MCU if you want it. Also have some left over EC2 connectors from the quadcopter that would be good for the heatbed.
Thanks @Laine_Walker-Avina I have a bunch of mcu’s, so that would work.
I think for now I will use a relay until I redesign teensylu.