|Posted: Sun Jun 17, 2018 6:47 pm Post subject: Z19 first try and smoke/wire melted I did a mistake
At 02:33 PM 6/17/2018, you wrote:
|If the OP had installed a "snapjack" rather than a diode on his battery contactor, would the contactor have closed, and delivered the reverse polarity current to the rest of the system? If so, then perhaps this is an argument in favor of diodes vs snapjacks.
Correct. A 'snapjack' is a zener/tvs device in series
with a diode . . . sometimes we see two tvs devices
back to back. The breakdown votlage for selected
devices has to be somewhat greater than system
voltage . . . so yes, this story might have
ended differently if something other than the
plain-vanilla diode were installed . . . or the
diode was not mechanically robust.
We generally don't incorporate reverse polarity
protection on battery contactors. Battery cables
are usually difficult or impossible to hook up
backwards. External batteries on jumper cables
is another matter.
I believe I've shown reverse polarity protection
on all the ground power circuits . . . some include
OV protection as well.
Bob . . .
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