board smoking and heated bed resistance low
the 15A fuse to my heated bed blew. i replaced it tonight, but the bed did not heat up. instead it just started smoking.
i unplugged it and found the resistance to be .4-.6ohms. I can't see a short. I cut the wire to rule out the wiring. I sprayed contact cleaner on it. no change. Any ideas? Or just buy a new one? I have never done copper tracing or whatever.
Re: board smoking and heated bed resistance low
the 15A fuse to my heated bed blew. i replaced it tonight, but the bed did not heat up. instead it just started smoking
The bed itself started smoking? Where exactly?
Correct resistance of the bed should be at least 0.8 Ohm to achieve max. 15A from 12V. If the bed without wires has 0.4-0.6 Ohm, there must be partial short circuit. Most likely it is the place where the smoke comes out.
Be sure you measured the resistance right and you decreased measured value by internal resistance of ohmmeter measuring cables (measure resistance of cables themselves first, then with bed, then do some easy math).
Re: board smoking and heated bed resistance low
It started smoking from the fuse.
My DMM's resistance is .1-.3. the value i got at the board was around .8. I measured at the solder joints on the board.
Would operating it at too high of a temperature cause this? I have turned the bed up to 90C before. Then i read online that the bed is only rated to 60C.
Re: board smoking and heated bed resistance low
Looks like your setup works near top edge of manufacturing range of parameters. The fact is that Rambo is not designed optimally to handle maximum currents for a long time. The board is OK, it is able to operate up to 110°C with no issues. I print ABS at that temperatures. But to keep high currents outside the control board, I use this helper to control heatbed power: http://www.banggood.com/3D-Printer-Parts-General-Add-on-Heated-Bed-Power-Expansion-Module-High-Power-For-Chitu-Motherboard-p-1086965.html
Re: board smoking and heated bed resistance low
would it work to just wire a relay that pulls directly from the power supply? or is it duty cycled and needs a transistor?
the only concern i have is that before the board started smoking, the bed did not actually seem to heat up. i may try actively powering it up with a jumper or a power probe to see if it is actually heating up.
Re: board smoking and heated bed resistance low
would it work to just wire a relay that pulls directly from the power supply? or is it duty cycled and needs a transistor?
It's quite fast PWM.
Re: board smoking and heated bed resistance low
Damn. I put a 14awg jumper straight to the 12v on the power supply and it worked like a champ. Then, I became worried about the unfused 16?awg ground side that controls it from the board. I didn't see a duty cycle on the DMM, so i was considering the relay option until you told me about the PWM.
Given that the control board only smoked when I had the 12v fuse in, do you think i might get away with putting a fused 14awg wire, or circuit breaker, on the ground side?
otherwise, the price of that heated bed controller was not bad at all.
Re: board smoking and heated bed resistance low
Given that the control board only smoked when I had the 12v fuse in, do you think i might get away with putting a fused 14awg wire, or circuit breaker, on the ground side?
I'm not quite sure what you exactly mean. Could you draw a simple scheme?
Re: board smoking and heated bed resistance low
Nevermind the ground side fuse
Re: board smoking and heated bed resistance low
i had it running through the stock ground wire for 20 minutes or so without issues. My main concern was whether i would be putting too much current through the ground side. I checked voltage drop. .8v at ground side of bed. about .6v at board. I think stepping up the gauge is definitely appropriate. I measured current. It starts at 15A and drops steadily.
it was the 12v side that smoked before, and after rewiring that, i have not seen anything similar.