user9253
Joined: 28 Mar 2008
Posts: 1921
Location: Riley TWP Michigan
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 Posted: Sun Mar 01, 2009 6:54 am Post subject: Diode across main contactor fat terminals |
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On May 23, 2008, I posted a hypothetical question about Z-19 main battery charging current back feeding through the endurance bus and blowing fuses in the event that the main battery contactor fails and the pilot closes the endurance bus alternate feed switch. http://forums.matronics.com/viewtopic.php?p=184591&sid=86e2d2ac21d95a18ce267b57c4fcd85e
To prevent the above scenario, what if a diode were placed across the main contactor fat terminals? If the contactor fails, this diode would prevent the main battery from discharging. What are the disadvantages? If this diode shorted out (diode failures are rare), then the pilot would lose the ability to shut off the master switch in case of an electrical fire. However, current would be limited by the lead size of the diode, similar to a fusible link. The chances of an electrical fire and the diode failing on the same flight are extremely remote. If one is concerned that the diode failure would go unnoticed at engine shut down, then a warning chime could be connected to terminal 3 of the master switch. I think the odds of the main contactor failing and associated pilot error (with dangerous consequences) are greater than the odds of a diode failing (with minimal consequences). What are your thoughts?
Joe
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