Testing for Catastrophic Capacitor Failure

Ground Sphere Mk2 PrototypeSometimes what would appear to be a great idea turns out to be not-so-great. I had a concept of bedding the Software Defined Radio (SDR) and pre-amplifier for the Ground Sphere Ground Station in Greatstuff foam to make it more resilient to shipping and other mishandling, similar to the way delicate equipment is shipped in a two piece conformal foam mold.

Jeremy Wright asked a very simple question that I had not considered… what would happen if something electronic fried? That’s not entirely true… I did think of that, and so I selected Greatstuff Fireblock. Then he asked “Did ya test it?” The simple answer is no, I had not.

It turns out that the fire resistance of fireblock is not the same thing as fire PROOF. The electronic design uses tantalum capacitors, and since these have the highest likelihood of bursting into flames if something particularly nasty happens (extremely unlikely), I wired one to a switch and 110VAC mains current for a test.

I used a fully cured foam bed made with Fireblock in a outlet box similar to what I am using for Ground Sphere’s base. I stuck a screwdriver in the foam to make a hollow and stuffed the capacitor in a ceramic base connected to the household mains. Yelling “fire in the hole!” was probably overkill, and oddly prophetic.

Now, the type of failure I generated in the capacitor would never happen in Ground Sphere. The capacitor was large, and the voltages 10 times what could be unleashed at a much higher current. In short, the test was going to be conclusive one way or the other. It was either going to combust in an epic manner or laugh in the face of Zeus, Prometheus, and I as we did our worst.

Long story short, we are NOT using Great Stuff Foam products to bed electronics. It is fine for house insulation (though I’d want to keep it far away from electrical stuff) and shipping delicates, but the fire retardant effects go away when confronted by an electrical fire that bursts out at over 1800 degrees.

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