RAMPS 1.4 MOSFET becomes very hot

Hi, I have a Monoprice maker select V2 and I'm doing a RAMPS upgrade. I have firmware on the Arduino and I've printed a couple prints with no heated bed. I tried using the heated bed for a print and smoke soon appeared. I found the MOSFET parallel to the blue screw connectors was extremely hot and was melting the plastic of a wire that was touching it. I turned it off. The green arrow is pointing at the MOSFET in question: https://imgur.com/a/G4sOQzk

My printer still works when it turns on. It homes axes and idles, but almost instantly, that MOSFET is unbearably hot to the touch. I've tried running a fan at it but it just gets so hot so fast.

What are the steps to take to troubleshoot this?

Its a design flaw with cheap ramps, particularly an issue if your bed is larger than the standard 200x200 at 11amp.

There are two options

1) replace the mosfet with something better eg IRLB8743PBF or IRLB3034PBF (requires soldering)
2) use an external mosfet eg [www.ebay.com] (just plugs in)

Edited 1 time(s). Last edit at 06/10/2018 08:47PM by Dust.

As Dust suggests replace the MOSFET with a IRLB8743BF or get a quality RAMPS like this one from StaticBoards

[www.tindie.com]

I upgraded both my printers with them.

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Quote
SteveRoy
As Dust suggests replace the MOSFET with a IRLB8743BF or get a quality RAMPS like this one from StaticBoards

[www.tindie.com]

I upgraded both my printers with them.

If you are even reasonably comfortable with a soldering iron, replacing the MOSFET is your best bet. External SSR's will work, but . Replace the MOSFET, they're cheap. The RAMPS board is also pretty cheap, just don't buy that brand again...

DLC

I've been looking for the IRLB8743 mosfet online but the only place I could find them at a decent price was on aliexpress with a 30 day shipping minimum

Anything on amazon where I could get it in less than a week?

EDIT: Found some on digikey.ca

Edited 2 time(s). Last edit at 06/13/2018 10:23PM by Stmcc.

I only run the nozzle on the ramps.
I simply use a relay (With a diode offcoarse) to let power through to the heat bed. The relay is easily accessible and can be replaced in a minute. This way my head bed gets raw power directly from the PSU. No transistors that steal heat away from the heatbed.

real relays tend to weld them selves shut, with internal arcing and such over a short time.

That's bad news