Reverse Current Protetion

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I have recently redesigned our product to run from a 12VDC automobile type battery instead of 110 AC. I am using an off the shelf motor controller to drive a 1/3 HP dc motor. The controller works great but has no reverse current protection. Connect the battery backward and the drive will be fried.

I am considering a diode in the ground cable to the battery in order to stop reverse current. Since this type of battery can drive some pretty high currents, I am concerned about heat and damage to the diode. I will appreciate your thoughts about this approach, appropriate diode selection, and perhaps better ways to get this done.

Thanks

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Presumably this reverse connection would only be occasional and accidental, not a daily occurrence, so why pay the power cost of a series diode? You might consider putting a diode in reverse across the power terminals, with a fuse - presumably you have a fuse - in series with the battery lead. The diode will short the battery and protect the equipment until the fuse blows, and a large (40A?) diode can probably stand over 400A for the few milliseconds it would take.

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You could use a P-CH mosfet.

http://www.irf.com/technical-inf...

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I think I like the reverse diode across the terminals idea. I like this one because there is no power loss so the battery will last longer, at least that is how I understand it. I am looking at Digikey for a diode. There is no amp rating in the search tool, only watts. I selected one (Digikey part number 497-4189-1-ND) with 15 Volt reverse standoff and a 5000 watt rating. I calculate (5000 watts / 12 volts) that this converts to something over 400 amps, did I figure that correctly?

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That is not the kind of diode you're looking for. It's like a 15V zener, intended to clip off voltage surges. For what it's worth, if you look at the data sheet you'll see in the Absolute Maximum section, "non repetitive surge peak forward current - 500A", which is the kind of rating you need here. But you need a conventional diode like the 65PQ015, which can handle a whopping 1500 amps for 5 microseconds or 400 amps for 10 milliseconds. If you don't like that one, just search for single rectifier diodes rated for 25 to 100 amps and check the non-repetitive surge ratings.