Blown Mosfets
I've been using an external MOSFET + heatsink with my MK2.5, as seens to be quite common. This worked fine for hundreds of hours.
However, 2 days ago I was printing ABS and noticed that the bed temp was 120C after a print had finished. It looks like the external MOSFET failed on and the bed kept heating. Quite worrying?! The 15a fuse also blew.
I bought a new MOSFET today and it worked again. However, the same problem happened an hour ago, another blown mosfet and a lot more damage. The plastic Rambo cover has melted, the mini Rambo may be a gonner and I'm lucky I caught it in time. The print bed was 115C and rising, but the MOSFET was crazy hot.
What on earth is happening? ABS worked fine before, the only change made was to upgrade to the 3.7 firmware, but I dont see how that could cause a hardware failure like this.
What should I check to see if I can fix this? I'm at my wit's end!
Re: Blown Mosfets
The PWM cycles changed recently to reduce power supply clicking. Chances are your chosen component was running at its limits and that pushed it over. Time to find one with better ratings.
... you DO have a heatsink on your MOSFET, right? Look at its data sheet and see whether one is needed for your operating conditions.
Re: Blown Mosfets
I've been using an external MOSFET + heatsink with my MK2.5, as seens to be quite common. This worked fine for hundreds of hours.
Any reason to use external instead of internal? Have you switched to 24V heat bed?
As already vintagepc mentioned the PWM cycle was increased. That brings already the original boards and capacitors to their limits.
In general check your setup. Blown MOSFET should lead to blown fuse and no power to the heat bed. You're running a dangerous setup.
Often linked posts:
Going small with MMU2
Real Multi Material
My prints on Instagram