Just switched over to a silicone heater + 4mm aluminum plate as well. The thermistor that was included on the bottom was pretty much worthless, as it would report 120C when in fact the aluminum plate was only at 105C jet, but then slowly crept up to 115C in the next half hour. I drilled a hole in the aluminum plate and installed a Semitec thermistor in there, v6-style. Spot-on readings, even if the reported heat up times are a bit longer (but more accurate).
150x150mm, 150W (at 12V), goes up to 150C. 15€. Much faster to heat up than a PrusaPCB. For 400x400 I’d probably use one that is around 1kW to get decent heat-up times.
Back on topic, I’d recommend grabbing a decent Mosfet and using that on a daughter board - there’s plenty of types available that won’t burn up with intense loads. Mechanical relays aren’t something I’d want to use for the type of temperature control we’re doing, and I’ve also seen quite a few people post about bulged SSRs in this community.
What have wire are you guys using for these loads, and/or are you experiencing the wiring getting warm while under load?
I’ve been using 2.5mm² silicone wires for each ~150W heated bed, along with the ~1.5mm² ones that the Alirubber mat was supplied with. Neither really get warm, but keep in mind that a certain amount of temperature rise is unavoidable and acceptable. For something like a 400W (@12V, so 33A) bed, the generally recommended size is 6mm² and up. For the same power at 24V (17A), you should be fine with 2.5mm².
@Thomas_Sanladerer weird. My thermister is spot on when checked with my multimeter w/ thermocouple. But that was at 110c. What table did you use?
I know several people using SSR’s with no issues. But a quality SSR is a must.
@Eclsnowman table 1. I could live with an offset, but the temperature kept slowly rising after it reported that it was up to temp.