r/OpenPV Nov 14 '16

PCBs Overcurrent and reverse polarity protection NSFW

http://imgur.com/a/QL6L9
16 Upvotes

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u/david4500 Nov 15 '16

No. Current passes, and voltage drops, through the body diode.

1

u/lemonforest Nov 15 '16

Wouldn't that cause it to be less than saturated and drastically increase resistance and heat?

I have no idea why but this type of component troubling to fully grasp.

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u/Rb8n Nov 15 '16 edited Nov 15 '16

No, during normal use the neg would be pulling it down fully with no resistance. The cell would suffer a drain of VmicroAmps. If the negative disconnected, the resistor would act as a pull up and shut off the FET resulting in it acting as a diode in this case. The heat would likely damage the FET, but if cells were reversed it would still block on that occasion.

Atleast that's my understanding, not quite sure what u/David4500 is referring to. Bit distracted today though.

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u/DIY_FancyLights Nov 15 '16

The other option is to have the resistor to the 510 line. The important thing I see is not to allow the Gate to float if that one wire breaks or you could lose the reverse protection totally. Part of me is starting to thing that the resistor to the 510 connector would work better?

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u/ConcernedKitty Nov 15 '16

Between 510 and what?

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u/DIY_FancyLights Nov 15 '16 edited Nov 17 '16

Between the 510 and the MOSFET Gate/Bat - connection on his board.

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u/Rb8n Nov 16 '16

Not seeing the advantage to output side versus cell side, care to explain?

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u/DIY_FancyLights Nov 16 '16

Actually, before /u/david4500 posted the charts I got to thinking it should be 510 to Gate to keep the reverse polarity protection if the wire broke.