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Old 18-05-2018, 16:05   #1
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Boat: Cape Dory CD28
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DC Reverse Polarity


After a long night out with some friends, I hooked up my boat’s circuit backwards: pos to neg, neg to pos terminal. I flipped the battery selector switch on and immediately saw smoke (luckily no fire), then I disconnected the circuit. Is there a particular area of the wiring I should check? Could I have blown the engine’s solenoid, alternator, etc?


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Old 18-05-2018, 16:26   #2
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Re: DC Reverse Polarity

Radios and electronics can fry. Some things have internal fuses for this.

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Old 18-05-2018, 17:10   #3
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Re: DC Reverse Polarity

Best you can do is hook it up correctly and turn everything on and see if anything doesn’t work, then start troubleshooting.
My kid did it in my Verado outboard, on it there was a fuseable link to the alternator that melted.
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Old 18-05-2018, 17:44   #4
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Re: DC Reverse Polarity

Incandescent/halogen lights don't mind which way the polarity is, LED lights do, but as far as I know nearly all are protected.
Electronics do mind, and will fry, if they were switched on. If they were 'off', they should be OK.
At the same token lots of electronic gear is protected anyway, if so: no problem for you.
I would check all items one by one, check all fuses too.
BTW, standard fuses would not likely protect the electronics from frying, the damage would have been done before the fuse 'melts'. It would protect your wiring if correctly sized.

Hehehe, boating and drinking may not be a good combination. I have three suggestions:
* reduce alcohol intake (making an assumption here )
* connect wires permanently to batteries and use the switch to activate the circuits
* if the above is not possible and if you want to protect some gear, google "reverse polarity protection", click on images, and you will find hundreds of diagrams, the simplest is the bridge rectifier (4 diodes in one package) that allows operation regardless of polarity, but drops the voltage by ~0.7 Volt, or a Mosfet without voltage drop.
Wishing you all sunny skies above, clear water below, gentle winds behind and a safe port ahead,
and when coming this way check,_Australia
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Old 18-05-2018, 17:54   #5
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Re: DC Reverse Polarity

Alternators and chargers need to be checked
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