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Rob's REBVAIR Project
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Date: 2-22-2016
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Number of Hours: 3.00
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Manual Reference:
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Brief Description: Over-voltage protection
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Over-voltage protection (OVP) is widely regarded as a cheap insurance against frying your avionics with a prolonged voltage spike from a faulty voltage regulator. I have no idea how often this occurs in 'real life' but most of my trusted references say it's worth having.
There are two OVP modules popular among homebuilders. I suspect BandC's OVP (seen here) is most frequently installed, but Perihelion Design's (PHD) version boasts a more 'elegant' trip device that acheives the same goal, and it also includes an option to reset the module in case the spike that caused it to trip was an anomaly.
It sounded good, so I purchased the PHD device. As recommended, I tested the device (no small feat) and as I went through the steps, one of them led to smoke coming from the device, and the the OVP would no longer trip 'off' from then onwards. In other words, its failure mode still allowed current to pass through the system, and it was getting very hot.
I couldn't think of a more dangerous failure mode, so I contacted the developer. He and I checked that I had wired things correctly, then sent me another module that I tested with a lower 'load'. That failed in the same way. To his credit, he is apparently testing units now after purchasing the same equipment I have, to see if he can duplicated the failure. That was a few months ago. No word since. In the meantime, I've installed the BandC device. It might be less elegant (apparently shorts to ground which is 'hard on the system' according to PHD), but it tripped off and stayed off when I hit it with 16.3 Volts. I have it connected to the system through D-sub pins so I can remove it for annual testing (as recommended).
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OVP unit to the left of blue capacitor
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