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Reversed Battery Leads

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dave2374

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When de-winterizing the boat this year the battery was connected wrong for about a minute. Said a few cuss words, but the engine started and ran fine. Took the boat out a few times for three short periods, maybe 2-3 hours of runtime total. The other day we went to take it out and the battery was dead. Got it jump started with a portable jump starter and drove it around a bit and it started hesitating, warning alarm sounded and it died. I was able to jump start again, but had to leave the portable jump starter connected in order to keep the motor running. Put the battery on a charger and the motor runs fine, for now. Voltage regulator? The motor is a 2019 40ELPT CT 4S.
 
Yepper on the diodes. The ones that have their anode tied to the case of the alternator have no resistance in their path when conducting in the negative direction from an external power source. In normal operation they have the resistance/impedance of the windings of the alternator to limit the current.
 
I did the same thing this spring. I connected the battery correctly every year for 17 years, until this year. (Duh - no excuse.) Anyway, I replaced the alternator guessing the diodes were destroyed, but still no charging joy. I'm looking at the Merc online parts diagram trying to find the voltage regulator but I'm not seeing it. I have a 2003 175L Opti (Serial 0T749593). Can anyone point me in the right direction? Thanks you!
 
I responded thinking about an automotive alternator whereby the rectifier and regulator are self contained. The Stator is an iron core coil and a magnet on the flywheel passes it. In doing so it generates an alternating,sinusoidal, power source...therefore it is an alternator. The difference in the auto and the marine application is that the Stator (alternator device) is floating not connected to ground (as is the automotive) and the diodes that get fried are in the rectifier/regulator module, not contained in the alternator housing like automotive applications.

So answering your question as to what else you fried, probably nothing but the Rect/Regl module. Hooking up in the reverse direction on a FW Bridge rectifier puts 2 forward biased diode drops, about 0.7v x 2 subtracted from the battery voltage and being forward biased, essentially zero resistance between your battery + and - terminals resulting in melted junctions and short circuits and then as they burn through, open circuits.

Sometimes folks have high current needs from their marine charging circuits and the two stator leads (on my engines,) are connected to the engine wiring harness via bayonet connections. As engines age and corrosion sets in these junctions over heat and burn and discolor the insulation on the wires attached to these connections. So, while you are there, might pull the connections apart and clean and lube them and reinsert for a good clean connection. Service manuals state the resistance range of a good Stator coil.....while you have the wires disconnected.

An auto came to my mind as I had a situation where I was on the road and had a charging problem due to a weak battery (in hind sight)....called the local filling station road service out to give me a jump start one morning to be on my way and apparently the guy was new at the jump starting task, put the leads on my battery one way not sure that was the right way so then the other way, still not sure, then back to the first (correct) direction. Somehow I got started and left. As I was getting to my destination after twilight with my battery voltage shot due to no alternator and a shot battery anyway, and the headlights getting so dim you could hardly see, oncoming traffic honking and yelling at me to turn my lights on....get off the road..... it wasn't a pleasant experience....and then I had to buy another alternator.
 
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Well perhaps the alternator I purchased was not good. I will admit I went for the $110 aftermarket product rather than the $650 Merc part. I was wondering if there is an external voltage regulator but I don't see one. There is a solenoid in the circuit. I ordered the shop manual so I hope there is a diagram in there.

I'm pretty sure the 2003 175L Optimax does have an alternator. It's driven by a serpentine belt and looks like every other alternator I have ever seen, but a little smaller. It's not a flywheel stator.

Thanks to all for the replies.
 
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SteveInMD said:
Well perhaps the alternator I purchased was not good. I will admit I went for the $110 aftermarket product rather than the $650 Merc part. I was wondering if there is an external voltage regulator but I don't see one. There is a solenoid in the circuit. I ordered the shop manual so I hope there is a diagram in there.

I'm pretty sure the 2003 175L Optimax does have an alternator. It's driven by a serpentine belt and looks like every other alternator I have ever seen, but a little smaller. It's not a flywheel stator.

Thanks to all for the replies.
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I don't have one of those nor have ever seen one but these thoughts come to mind:

If you just have pickup coils and are only dealing with sine waves, based on similarity with other marine engines of mine, the output of the alternator will be 2 wires of equal color and size, neither of which attach to 12v nor engine block ground.

If the alternator contains rectifying and if so probably also regulation (why wouldn't regulation be right there also), then you will have a red and black wire exiting [maybe an additiional small red wire (power input) for circuit excitation for the RR], one feeding the 12v distribution buss whereever that is (3/8" input stud to starting solenoid on my engines), and another (black) wire tied to engine block ground.
 
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