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Discussion Starter #1
I am having a problem. My alternator seems to be overcharging my system. I have had the alternator and voltage regulator tested, and they work perfectly. But when I put them on the boat, I get up to 18 volts.

It is a Volvo Penta 2002 engine, with a ParisThune alternator/regulator.

Has anyone seen this problem before? What could be causing it?
 

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Discussion Starter #3
That should be a Paris Rhone Alternator in my original post.

It is an intenal regulator, attached to the back of the alternator. I've had the regulator tested at an auto electrical shop, and they can't find any problem with it. But when I put it back on the boat, I get the overcharging problem.

There are four connections on the back of the alternator/regulator. Does anyone know how these interact? How does the voltage sensing work in these alternators/regulators?
 

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Don Radcliffe
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What does it say on the terminals in the back of the alternator??

Common Alternator Wiring Terminal Letter Designations

B+ , 30, Battery Positive
S, M, 2, Battery Voltage Sense
B- , 31, D-,GRD Battery Negative
F, DF , 67 , FLD , EXC, Field/Rotor
D+, 61 , L , IND, Charge Warning Lamp
DFM , FR, SIG, C, M, Digital Field Monitor output for computer ECU control
IG, 15 , R , Ignition
N, C, Central Point
W, P, STA, Tachograph rev counter (stator single phase tap AC output)
D Dummy

Paris-Rhone is French, so all bets are off. The voltage sensing is usually internal on an alternator-mounted regulator, but if it is an external wire and you haven't hooked it up properly that would explain your symptoms.
 

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Discussion Starter #5
We've isolated the problem down to the tachometer, but we're not sure why the problem arises. When I disconnect the tachometer wire, it works fine. If I reconnect the tachometer, the overcharging becomes a problem again.

Has anyone seen this behaviour before?
 

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What is the identification stamped at each lead on the rear of the alternator? Even French electronics have some identification on each lead, that would be a start. Also, what do you have them connected to, besides the tach?

Running 18VDC on a 12V nominal system for even a short length of time can cause a lot of damage very quickly, blowing out the electronics and every light bulb on the boat. You really, really, don't want to let it run that way.
 

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Don Radcliffe
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Maybe some history would help too--did it ever work, when did it stop working, and what did someone do to it or near it just before it stopped working.
 

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Maybe not correct but I get the impression that the battery voltage immediately or in a short time frame rises to 18 volts when the tach wire is connected.

If unregulated, the alternator could only put out near its max rated amps. Also don't know details but assuming the alternator is under 100 amps, it seems pretty unlikely that this could cause the battery voltage to jump to 18 volts (unless your doing this at VERY cold temperatures - like considerably below freezing).. My charging system is much lower so am guessing but would expect that you would see no more than a volt or two rise in healthy battery voltage for max current out of the alternator in the short time frame.

If you are seeing 18 volts, I would suspect something other than the alternator/regulator - like maybe a bad ground between the battery and the alternator?? Have no idea how the tach wire plays into this however..
 

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Discussion Starter #9
Looks like it was the alternator/regulator after all. The "experts" insisted it was all right, but noone could give any other explaination. After two weeks of frustrations, I broke down and bought a new alternator. Now it works perfectly.

Thanks for the responses, even though I was running around in circles chasing my own tail.
 
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