New alternator mystery - high voltage

[NatySailor]

Can anyone explain why I'm reading 17+ V out of my new alternator (purchased from Moyer within the last two weeks)?

I'm getting this reading with a multimeter where I have the red lead on the output "B" terminal of the alternator, grounded on the engine block.

When I check the voltage at the solenoid large terminal, I get around 12.5V. My built-in (Moyer/analog) voltmeter also reads 12.5V, so does a little additional voltmeter which plugs into the cigarette lighter adapter. (To be clear: all of these reading are with the engine running).

The batteries are freshly charged, and I get the same reading with the battery switch set to battery 1 (start) or 2 (house)

I double-checked the wiring today (which was redone recently), and the only departure from the Moyer wiring diagram, is that the alternator output "B" terminal goes directly to the large terminal on the solenoid, instead of through an amp meter and the "batt" terminal on the ignition switch. (And I'm pretty sure this is what the directions on the alternator said to do if you don't have an amp meter).

The engine starts and runs great, but with this high reading I'm afraid to damage my batteries and electronics.

Can anyone explain this so I can relax?

Thanks in advance!
Dennis

P.S. I did not buy the high capacity alternator that Moyer sells, it's the $230 model, and this is an early model engine.

[ndutton]

Is there any chance in the past two weeks that the battery was switched off with the engine running, even for an instant?

[joe_db]

Alternator - 17 volts
Battery - 12.5 volts
These two things are not connected to each other

[NatySailor]

Alternator - 17 volts
Battery - 12.5 volts
These two things are not connected to each other

Except as a way to double-check the reading coming off the meter.

[NatySailor]

Is there any chance in the past two weeks that the battery was switched off with the engine running, even for an instant?

Almost sure not. Are you asking because that could damage the alternator/voltage regulator?

[ndutton]

Are you asking because that could damage the alternator/voltage regulator?

Yes. Your symptom, although not yet conclusive, is typical of damage due to a voltage spike from running without a battery connected. Can you provide either pictures or a diagram of your actual installation wiring so we can have a better look?

[tenders]

Except as a way to double-check the reading coming off the meter.

I think Joe means that your double-check has failed. You can't be showing a 4.5 volt differential between two places on the same circuit. If the batteries are reasonably fresh, 12.5 volts is a sign that the alternator isn't connecting to them. 17 volts from the alternator is ALSO sign that the batteries aren't connected to the alternator.

Bad connection from the alternator? Broken wire? Badly corroded wire from alternator?

[ndutton]

Hey Naty, any resolution?

[joe_db]

I think Joe means that your double-check has failed. You can't be showing a 4.5 volt differential between two places on the same circuit. If the batteries are reasonably fresh, 12.5 volts is a sign that the alternator isn't connecting to them. 17 volts from the alternator is ALSO sign that the batteries aren't connected to the alternator.

Bad connection from the alternator? Broken wire? Badly corroded wire from alternator?

Exactly - there is no way you can have that much differential across a reasonably intact wire. If you got a Moyer one-wire, run a nice thick wire (8 gauge or thicker) straight from the alternator to the heavy battery cable connection on the starter and then tell us what you get.

[Al Schober]

In all this voltage checking, don't forget to check the other side of the circuit - the ground between the engine/alternator and battery negative. I've had strange things happen because of a) bad ground between alternator and block, and b) bad ground cable to/from engine.

[tmcdonagh]

Voltage reads 16+ volts

I ran into this same problem this weekend while motoring back to the mooring. My new Balmar smart gauge that was throwing code 4 (Battery voltage above acceptable level for selected battery type). My chartplotter was also displaying 16V. I was charging my house battery. As I was in a rocky inlet, I had no choice but to continue on. When I could safely stop the engine but still not at the mooring. I switched the battery selector to both, restarted the engine and continued on. At that point, the voltage was 13.5 volts. After picking up the mooring, I stopped the engine and noted the voltage drop for both batteries at 12.7 volts after resting. All connections seemed secure and no changes has been made other than connecting the Balmar. Suggestions?

Thanks,

Tom
s/v Servus

[joe_db]

Describe your alternator and regulator setup. My regulator will do this if the sense or ground wires get loose.