![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
You have to laugh to keep from crying.
Sep. 12th, 2011 10:12 pmAn interesting evening of RepRap activities. I got my 24v power supply in today, so I thought to just hook that up quickly, do a test and then get some other crap done. I hooked it up and set the print bed temp to 110C. WOW it shot up there in about 70 seconds instead of 20 minutes.
Then about 10 seconds later the circuit board started to hiss and smoke.
The MOSFET that drives the high current stuff is good for 60A at 55 volts, but it needs a heat sink to drive 360 watts. It had cooked itself (shorted) besides damaging the circuit board a bit. I only had P channel MOSFETs sitting around. So I stole one from the unused fan control channel next door, then cut down an old 386 heat sink and attached it with Arctic Silver heat sink compound (and an M3 screw). See photo. OK, it's probably a bit much but I was nervous. I think I may get some more reasonable, proper TO-220 heat sinks for it.
With that in place I resumed testing carefully and all was well. The heat sink only got marginally warm. All was good.
For 10 minutes. Then the glass cracked. Thin window glass does not like this kind of heat. The guys on the IRC channel say that 3.5mm glass from Lowes works great and costs < $4 so I'll get that tomorrow.
Documenting this all here because I want to put it all on the Wiki once I make all possible mistakes :)
( G+ comments after the cut )
Then about 10 seconds later the circuit board started to hiss and smoke.
The MOSFET that drives the high current stuff is good for 60A at 55 volts, but it needs a heat sink to drive 360 watts. It had cooked itself (shorted) besides damaging the circuit board a bit. I only had P channel MOSFETs sitting around. So I stole one from the unused fan control channel next door, then cut down an old 386 heat sink and attached it with Arctic Silver heat sink compound (and an M3 screw). See photo. OK, it's probably a bit much but I was nervous. I think I may get some more reasonable, proper TO-220 heat sinks for it.
With that in place I resumed testing carefully and all was well. The heat sink only got marginally warm. All was good.
For 10 minutes. Then the glass cracked. Thin window glass does not like this kind of heat. The guys on the IRC channel say that 3.5mm glass from Lowes works great and costs < $4 so I'll get that tomorrow.
Documenting this all here because I want to put it all on the Wiki once I make all possible mistakes :)
( G+ comments after the cut )
