Fire in the Hole!
My delta printer just about burst into flames in the middle of a print job. The printer was modified many months ago so it could use a heated print bed for printing ABS. I discovered soon after the modification that the controller, which is located under the print bed, could not deal with the extra heat when the printer was used for ABS printing. It worked fine about 50 – 60 degrees Celsius, but any higher the controller would eventually go berserk and die from heat stroke.
So, it has been running with only a 50 degree bed temp for about 10 months.
The printer was running for a couple of hours and I started to smell a chlorine odor. I thought my wife was doing some sterilization of counter surfaces out in the kitchen. She is usually generous with the Lysol spray. I investigated and discovered she was not doing that or even near the kitchen.
As I looked for the source for the chlorine, I gradually worked my way back to where the printer was running. The smell was now very strong.
Then I saw the print had loosened from the bed and I had a printer crash. Filament strands strung out all over. The I saw the bed temp on the video display was indicating about 170 degrees! Holy cow! (I didn’t exactly say cow…)
The heavy duty switching transistor on the Arduino board had shorted and delivered full ON to the 12-volt printer bed heater. The thermistor sensor had not failed, as it was showing the unbelievable high bed temperature. The switching transistor was obviously blackened and burned and the connector for the bed electrical feed wire connections on the Arduino had melted. The chorine smell was coming from the hot Arduino circuit board, the very hot printed circuit bed heater, and the melted plastic wire connector. I think most of the chlorine came from the bed heater (I couldn’t touch it or the glass it was heating). After it cooled I don’t see any scorch on the bed heater.
Amazingly the Arduino is still functional except of course for the switching transistor. I have the printer back in operation without the bed heater. I can still print PLA plastic.
I think the Arduino will be much more comfortable without the heated “ceiling” above its head. I will continue using the damaged controller as long as it works. I of course won’t be surprised if I must replace the Arduino.
I am currently doing some long printer runs on the Delta to be sure of its long-term stability. So far so good.
With the heater removed I had to re-calibrate the bed height. Now I can see through the clear glass and watch the controller LEDs blinking. It’s a little unnerving to not be able to accurately judge bed height visually, but the Delta holds its bed zero setting very accurately and for a very long time. I can get used to the clear printing surface. Oh, it does still have the PEI film on the glass. That might have been the chlorine source too.