Batt switch off, engine running, fire! - SailNet Community

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Go Back   SailNet Community > On Board > Gear & Maintenance > Electrical Systems
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  #1  
Old 07-20-2012
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Exclamation Batt switch off, engine running, fire!

Somehow, no one remembered to turn the battery switch on before departure. My 1974 Catalina 27 (major re-work done by previous owner in the 90's) has an Evinrude 9.9 O/B motor with alternator. The motor just had annual service and was put back on the boat/electrically re-connected. When we departed the pier and revved up rpm's, the marine radio began to smoke pretty good. I turned off the master switch and looked at the battery switch...it was off The radio is now operating with lots of static when on battery, better when on engine power, the depthfinder has gone totally blank at all times. What did I just do to my boat? What should I do now?
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Old 07-20-2012
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Re: Batt switch off, engine running, fire!

Sounds to me like you smoked your radio and depthfinder.

Alternator regulators increase alternator output as battery voltage decreases. No battery = zero voltage = maximum alternator output. Apparently way more output than your radio or depthfinder could tolerate .

Probably not what you wanted to hear, but it sounds like you need a new radio and a new depthfinder. You'll want to have the outboard's alternator checked, as well, because you might have damaged one-or-more of its diodes.

If the outboard's alternator has an alternator field input that can be disconnected, look into a new battery switch--one that has alternator field disconnect (AFD). That way if the battery is off, no voltage from the alternator.

Jim

Last edited by SEMIJim; 07-20-2012 at 11:21 PM.
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Old 07-21-2012
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Sounds like the regulator could have failed as well and smoked everything that was "on", you might want to check lighting, wiring, etc for any other damage. Good advice to check the battery switch field circuit if used.

Last edited by sea_hunter; 07-21-2012 at 06:27 AM.
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Old 07-22-2012
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Re: Batt switch off, engine running, fire!

With no battey connected, the voltage from the alternator will be much higher than 12 volts. That would have damaged the electronics.

I would look at how the engine alternator is connected to the battery. Sounds like its connected to DC Panel. If the alternator is connected directly to the battery, it would not power the DC loads unless the switch was ON and this won't happen again.
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Old 07-22-2012
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Re: Batt switch off, engine running, fire!

Exactly!

Wiring is wrong. Alternator output should go directly to battery, with appropriate fuse.

No power should go to radio, fathometer, etc. unless battery switch is ON.

Bill
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Old 07-22-2012
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Re: Batt switch off, engine running, fire!

Amen. "fortunately" you just lost a depthsounder and possibly radio, but now you know the boat is wired incorrectly AND you could have lost the entire boat.

Personally, with that kind of wiring error I wouldn't trust an inch of the electrical system until I had checked it all out, with hands and eyes, and confirmed there are no other little tricks.
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