Thursday, April 21, 2011

April 21, 2011

I replaced one of the broken TIP120s on the pwm heater boad with a MOSFET, testing with a multimeter looked like it was working properly, so I connected it to the heated on my extruder. Testing that proved, or created, a short in the nichrome heater somewhere. Instantly smoked and fizzled. So I killed it and left it to today.  I have it dissected so far, and I did not find the short, but there was a blob of black PLA where the PWM leads connect to the nichrome wire, so it could have been in there... or something else made a terrible smoke, acrid smell, AND killed the heater... maybe a tiny Genie... for my First wish, a thousand more wishes and my Second; a simpler to disassemble hot end with a resistor heater block, and Thirdly; a peanut butter, banana, cream cheese sandwich.

Since I still have an amount of nichrome wire I'll just have to rebuild the same design.  I might as well get some pictures of what I've been doing to wrap my hot end.

18 awg red wire
12 awg green wire
nichrome wire
brass barrel & nozzle
Kapton tape
Pipe clamp
PTFE Thermal Barrier
The length of nichrome wire is 14.0 ohms
But my multimeter is a little off
About 43 cm long
43cc/(14ohm - 2.3ohm) * 8ohm = 29.40cm
Only use for 12 awg wire, some 4-5cm strands
Bend a hook on nichrome wire end
Slide hook into 18awg red wire, then twist to hold wire in place
Using the small strands to wrap around the nichrome wire and 18 awg red wire
Some solder to hold it all together. Doesn't matter now if nichrome won't solder
And the other side, then wrap both in Kapton tape
Wrapping the nichrome wire from half-way down to nozzle. Easiest when held in a small vise
Kapton the nichrome wire onto barrel
Wrap in ceramic insulation tape and kapton
Kapton to hold the thermistor
The glass is touching bare brass on the nozzle, more kapton to hold it.
More insulation tape & Kapton, then the thermal barrier

Woohoo all done

It looks like it's working now, the one pwm circuit that I thought I fixed the other day is stuck on now, and there's a burn spot... which is the channel the heater was connected to when it shorted. More things to fix. Anyway switched to another pwm channel, and it heated to 40C, then held there.  I'll try something more ambitious tomorrow.

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