Both big mosfets and one small mosfet now not working

smoothie-forum
(jh628_SW) #1

A few days ago I managed to overshoot the config defined max temperature for my hot end- this caused things to shut down and I got a fault/warning in Pronterface, but now the small mosfet I had running the hotend and the LED above it are constantly powered. I read about this happening to a few different people, so it is nothing new. The small mosfet looks burned.

I noticed my more recent trouble toward the end of a 26 hour print. Both the input connector and the big mosfet connecter (2.5) for my heat bed were burned partially black. The print finished, but once the power to the bed was cut, it was gone forever. I can no longer get either 2.5 or 2.7 to power up- the LED stays off and I can measure no voltage. I am getting 12 volts to the input connector still. I re-read the setup instructions and noticed that I glazed over the fact that the mosfets require cooling if drawing more than 12 amps. I did the calculations and my current 12 volt, 270 Watt heater overshoots 12 amps by a bunch. Huge mistake on my part.

I have on the way from China a 110 volt silicone heater I had planned to run with a solid state relay, but with just one functional small mosfet, I can run either a hot end or a relay controlled heated bed, but not both.

There is visible discoloring on the board and a few components radiating up from those scorched connectors. Is it likely that a lot more than just the 2 big and one small mosfets need to be replaced (plus the burned connectors)? It seems like two different problems since the small mosfet is always on and the big mosfets are just dead. I successfully completed a print with PLA last night, so the board seems to function just fine other than the loss of the mosfets. Is it worth buying the replacement parts, or do I need a new board?

Imported from wikidot

(jh628_SW) #2

Is there no one that can give some insight on this?

(DaveyMaker_SW) #3

it’s not clear what you’re looking for. I don’t know how badly the board is damaged, nor where, nor what your skill levels are. Iffin’ it were me, I’d wire up some new MOSFETS mounted external to the board. You may need to wire in those ‘few components’ either on the board or externally.

(DaveyMaker_SW) #4

I’d consider wiring the new heater up to a separate digital temperature controller. some have outputs that could probably drive the heater directly.

(Arthur Wolf) #5

Hey.

You don’t need a mosfet to control a solid state relay, any GPIO pin will do directly ( see the 3D printer guide ). This means you can just use any free GPIO ( or the GPIO of one of the burnt mosfets ) to control the SSR, and use the available small mosfet to control the hotend.

Cheers.

(jh628_SW) #6

Thanks DaveyMaker and arthurwolf.

I got replacement connectors and mosfets in the mail and decided to go ahead and replace everything that looked damaged. I managed to pull a pad off the board when removing the small mosfet. I found the resistor the schematic said the pad connected to and soldered a jumper wire to it. Everything appears to be working as normal now. The surface mount soldering was tricky and doesn’t look really pretty, but I am glad to have more options now.

Thanks again.