Re: reverse polarity protection (ubitx.net)

Jerry Gaffke
 

My preferred solution:
    https://groups.io/g/BITX20/message/52904

The instructions for reverse polarity protecton on the uBitx WireUp page would be acceptable  
if they also showed a 3 Amp fuse in line with the +12v lead from the power supply.
A large Schottky would be preferable to a 1n4007 if using a shunt diode like that,
a 1n4007 at significant currents might have a forward voltage of a volt or more.

The drawing at the top of the polarity protection page on ubitx.net is wrong and best ignored:
    https://ubitx.net/ubitx-fix-reverse-polarity-protection/
I see two issues with that drawing:
1)  Jack has  +12v going through the barrel of the connector, that's not typical.
2)  If black is truly ground (as it should be on the provided wiring harness) then the shunt diode is reversed in the drawing
 
For a shunt diode scheme like that, be sure to have a fuse in the +12v lead.

A few people recommend a fuse in the ground lead too, but equipment grounding (3 wire plugs, RF ground rods, etc)
can give a path around that ground lead fuse.  I never bother.
 
Jerry

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