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Fried heatbed mosfet

Posted by vitorbrazil 
Fried heatbed mosfet
February 05, 2018 10:55AM
Hi, I'm building a 3d printer, I finished everything, tested the steppers, turned the heatbed and extruder on, both heated nicely. So after regulating the bed, I opened pronterface and started printing. Everything was going fine, extruder and bed were still heating up, when suddenly smoke starts coming out of ramps. I shut everything down, and I can see that the heatbed mosfet is fried, it even melted the plastic connector from the heatbed a bit. But everything else is fine, no burned polyfuse(from the looks of it), steppers working normally, the only thing that fried was the mosfet.

Now, I wonder what caused this, I tested the bed afterwards, it had a resistance of 1ohm, every other component is fine, no sign of shorts. Could this be a simple component defect, or should I look for another problem. I'm not sure how to proceed, I will replace the mosfet and try again, but I'm afraid of damaging the rest of the board, this time I got lucky.

My heatbed resistance, according to the manufacturer, is 0.8ohm(I measured 1ohm, but my multimeter smallest scale precision is 200), so that would give about 15amps of current draw.

Edited 1 time(s). Last edit at 02/05/2018 10:56AM by vitorbrazil.
Re: Fried heatbed mosfet
February 05, 2018 11:59AM
... too much power, insufficient cooling...

Re: Fried heatbed mosfet
February 05, 2018 12:24PM
15 amps is almost certainly too much for the heatbed connector too, particularly if it's a cheap Chinese RAMPS.


{Precision Piezo} Accurate, repeatable, versatile z-probe plus piezo discs, endstop cables, pt100, 50w heaters.
Re: Fried heatbed mosfet
February 05, 2018 12:34PM
Replace the mosfet be sure to add a heat sink this will assist the mosfet in keeping cooler. Myself I added a fan to keep the all components cooler.
My controller is different than your but I too added a heat-sink on my Base v1.3 and MPS.3 controllers as they were running too hot for my liking.
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