Thermal testing in thermally conductive resin

March 17, 2014 in 8 Channel PDU by Joshua Oster-Morris

I did another several hour test to see how a Motobrain cast in thermally conductive resin responds to high current loads. The test was similar to last one where I started at 50A and began taking regular readings and when I saw the temperature was stabilizing I turned it up 10A. The results are below. The maximum temps are much lower now than with the previous resin. This stuff is clearly allowing more heat to radiate off the device keeping the max temps in check (10 degrees lower inside and out with this resin compared to the previous) while also reducing the thermal gradients across the device which will improve MTBF in the long run.

The top was measured with the FLIR camera. The side was measured with a Fluke thermocouple. The internal was measured with a sensor on the MCU.

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Here you can see the lab in the IR spectrum. The wires are straining under the current load. You can even see the two AC power lines I an running to the power supply to reduce the fire hazard.

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This is a photo of the fake ignition switch I use. It is really a couple of series diodes that do a fine job convincing Motobrain that an alternator is running or not. All the current also flows through this and boy was it unhappy. 85C is HOT!

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That is as hot as the Motobrain got over 2 hours of testing up to 90A.

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I planned to do the test up to 100A but the power supply started to make “creaking” noises and I got nervous and shut it down. I am a bit intimidated by what Motobrain can do. 1300W is a ton of power! Still I did turn it up to 100A and took snap shot. It did the deed and didn’t burst into flames. Kudos to you Motobrain. The internal temp was 44C.

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I even did a little cold temperature testing. I put it in the freezer for 20 minutes and then powered her up to see what would happen. No drama at 4C. I’ll need to do more of this but the preliminary testing I’ve done (down to -80C) has all been positive.

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