Gen7 Research
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This page shows some of the research done for developing Generation 7 Electronics. It may be helpful for developing other electronics as well.
Contents
MOSFET heat
With heated beds becoming more and more standard, MOSFETs are used to switch currents in excess of 10 Ampéres, sometimes 15 A. While MOSFETs exist which claim to be capable to switch much higher currents, it has been shown they require a careful integration into the electrical design of the electronics. To get to the bottom of this, I've done a few measurement series', measuring heat development of a MOSFET in different configurations.
Markus "Traumflug" Hitter, February 2012
Test setup
The electronics used to do the tests was an older Gen7 v1.2, which first had to be fixed.
The heated bed were two undersized test beds, soldered together. Together they had a cold resistance of about 1.2 Ohms, requesting about 10 A at 12 V.
The power supply was a generic 250 W PC-PSU, specified for 13 A on the 12 V-Rail.
The MOSFET was equipped with a heatsink made of a flat sheet of painted aluminium to give good exposure for a phyrometer, a touchless thermometer. The contact point between MOSFET and heatsink was carefully cleaned from paint, of course, but no thermal paste was applied. It was taken care to not blow against the heatsink to not falsify temperature measurements.
The cross on the heatsink was a mark to ensure the temperature reading was always taken at the same place. The next picture shows how this was done. The red spot is a pointing laser built into the phyrometer.
As the heated bed was undersized, it gained in excess of 150 °C on first tests and started to fume. So a fan was placed underneath to cool it. The maximum temperature reached was something like 80 °C, but not measured.
Overall the test equipment wasn't made of precision instruments, but very well in the range of giving quality and approximated quantity results.
The heat wasting bed.
The heatsink.
Taking a temperature measurement.
