My @Printrbot Smalls has the upgraded heated bed. A couple questions:
a) Current handling of the board: I’m reading > 20A ! heating the ~6" bed. That is almost the current of the ~8" printrbot bed I’ve added to my Simple. When I put the larger bed on the Simple I bought a heatsinked DC SSR to handle the current. When I bought the Smalls heated bed upgrade, I assumed the mainboard can handle the current - I’m hoping I’m right!
b) Auto level / bed / Z sensor - not very sensitive. To get it to work I have it about 0.1mm higher than the tip of the printer. Any little curling or blob on a print will strike the sensor. Anyone else have that problem? If I raise it anymore the head will strike the bed before the sensor triggers. Can I file/sand some of the yellow/amber coloured coating on the bottom to give myself a bit more clearance?
If you are drawing 20A on the heatbed, turn everything off immediately, and replace the heatbed, it sounds like you have a dead short on it, or a short somewhere else.
This is likely to be the issue for your bed probe.
What is the resistance of the heatbed? Do you have a picture so I can test some here? If the board is bad, we can replace it.
The sensor: a springsteel plate would react differently that’s aluminum if you want to set the sensor higher. When we add the spring steel plates, we have to move the sensor up quite a bit. It’s so low b/c aluminum isn’t as reactive since it’s less dense. That said, we don’t have a problem w the sensor height as it is. I get nervous sometimes but if blobs or warpage are a problem causing collision , that’s a different problem.
I just backed the sensor off one full turn, and it still senses the aluminum plate. So we’ll see how it goes.
As for the heated bed, yes, I’ll try and get some photos tonight. I don’t have a multi-meter that can reliably do <1.0 ohms. But Ohm’s law would suggest the complete path is just over 0.5 ohms. (12V/20A = 0.6ohms). The bed heats up evenly (and quickly!). I’m guessing it’s a 240/250W heated bed?
The board on the Smalls is fine (so far) - just nervous about the rating of the power transistor (without a heatsink) and the power connectors.
The setup already smoked a poorly soldered barrel connector that I initially setup.