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Go Back   SailNet Community > On Board > Gear & Maintenance > Electrical Systems
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  #1  
Old 07-10-2010
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Help, wierd electrical problem

In a hurry I mistakenly hooked my batteries wrong today. Accidentally, connected positive battery cable to negative terminal in a 2 battery bank. Melted the negative terminal of the second battery. Yikes!!. Lights still worked but instruments and radio didn't. Radio circuit breaker tripped and blown fuse. Realized polarity problem when testing lead to radio and multimeter display -12volts. Oops. Hooked up remaining battery correctly and all was well except for instrument panel lights and warning alarm for engine. Engine panel is from Yanmar and now the lights go on and the alarm sounds when I flip the main battery switch. This happens with no key in the ignition. If I put key in the ignition and hit the starter every thing is fine, engine starts, no more lights and alarm. Anybody got any ideas as to what is going on?? I need help quick as I am transporting the boat on Wednesday about 120 miles.

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Old 07-11-2010
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I'd suggest checking each wire to the Yanmar panel. There may be a fuse blown or even a wire melted causing the alarm to sound.
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Old 07-11-2010
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Connecting 12 volt battery terminals in parallel maintains 12 volts but increases capacity by the sum of the capacities of each battery in the bank. Connecting the terminals in series, increases the voltage by the sum of the voltages of the batteries in series (roughly). Connecting two 12 volt batteries in series will have increased the voltage to 24 volts and may have damaged equipment not capable of dealing with the higher voltage. On one occassion at our club in SoCal (ABYC) one of the members made the same mistake on the club's flagship and wiped out all of the instruments, radio's et al. Good luck...
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Since the terminal melted it sounds like he created a dead short. A proper series or parallel connection would not have done this. It's a good thing the battery didn't explode or an electrical fire didn't start. I agree with mitiempo - the engine panel has to be inspected. There's no way of tell what damage occurred with only the above information. I think there is more than a blown fuse. The instruments and radio could very well be toast. Try running power directly to them with some test leads. The wiring needs to traced out, inspected and tested starting at the battery and proceeding logically through the system.
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Make sure the test leads have inline fuses!
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If he was reading -12v at the radio terminals, then it sounds like he connected the feed from the parallel batteries in reverse. The radio has a reverse polarity protection diode in it which would have blown the fuse as well as trip the breaker. The diode is now likely shorted. Check for a dead short across the power leads from the radio. If shorted, you will need to clip the diode out of the circuit inside the radio and hope no other damage was done to the radio. If this is the same battery bank used for the engine circuits, reverse polarity would place a dead short across the battery after turning on the battery switch via the diodes in the alternator. This would trip the breaker or blow the fuse in the alternator main positive lead if there is one as well as possibly blow the alternator diodes. If there is no overcurrent protection in the alternator output circuit, it would most assuredly blow the alternator diodes. It also sounds as if the ignition start switch is shorted. If the ignition switch is off, there should be no power to the panel indicators and buzzer. The buzzer and oil pressure and alternator lights should normally come on when going to the on and start positions and should go out/off once the engine is started.

Eric
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Old 07-11-2010
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Luckily, the wire looks pretty good. Radio fuse was blown as well as circuit breaker. All working now including instruments and sailcomp. I'm a pretty lucky guy. Now for the bad news- Diodes in alternator most likely blown. checked alternator output and no increase in voltage showing. Blown diodes might be the reason engine alarm is sounding. Engine starts and runs fine. Dropping off the alternator at local alternator shop for possible repair Monday. Everything else looks o'k include cables which I am replacing as a precaution. New battery. New alternator if I can't get it repaired. Alternator was pretty easy to get off. Engine is a Yanmar 2GMF.

Thanks to all that have contributed.
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