Hotend heat MOSFET on constantly after initial test

Controllers Smoothie
1

I assigned hotend heat to one of small Mosfets, P 2.6. Heater is 24v 40 watt heater, kinda big, but it’s a large printer. When I turned on the extruder heat, it heated up but overshot the target temperature badly, so I pulled the plug so it wouldn’t ruin my hotend. Now when I power up, the Mosfet LED is constantly on, as is the juice.

I’ve fiddled with the config to turn off the Mosfet completely, but to no effect. I’m guessing it’s fried ? The docs say it should handle 7 amps, a 40-watt heater should be less that 2 amps. I’ve got all the big Mosfets available, so I can move it over to one of those…

Meter shows the heater resistance to be 10 ohms, which is a little lower that the 14 ohms I calculate for 40w@24v. But that’s still only 2.4 amps of load.

I don’t see how I could have messed it up. I had left the PWM setting commented out, could that have somehow contributed to it ?

Thanks,
MTG

Imported from wikidot

2

Hey.

Could you try using another mosfet and see if it works there ?

Cheers.

3

As already suggested, try a different Mosfet, but likely it is fried. My first board I received had a bad Mosfet. It is not too terrible to replace the Mosfet (if you have a rework station) if you need all the connection, but otherwise, just use different ones.