Alternator Over Charging question

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Max Simmons

Max Simmons

Guru
Joined
Oct 15, 2007
Messages
819
Vessel Make
Ocean Alexander 38'
Headed out this morning for what was to be 5 days out on the hook. Leaving the marina, we turned on the inverter to keep the fridge running and charge a laptop. Inverter did not come on and the panel indicated "Fault". Voltage issue was indicated. At the DC panel, the voltmeter was showing 16 volts. I took the multimeter down and checked at the alternators. Port showed 16 Amps, Starboard shows 12.2 Amps.
Port alternator charges the house battery, which is what the inverter runs off of.
I shut down the Port engine and read DC panel with only Starboard engine running, voltmeter shows a little over 12V.
Shut down Starboard and run Port only, DC panel shows 16 volt.
I figure that the Port alternator is toast so return to port, pull alternator and take it to the local shop for testing. They put it on the tester and run it through the paces and say it's fine. Suggest that I check the sense wire to see if it is showing a drop in voltage. I went back, reinstalled the alternator and checked the sense wire, it shows 12.1 volt, while the output continues to show 16 volts.
Right now I'm questioning the shops testing. They said that it was showing 14 volts that was good.
Maybe voltage regulator is bad? I plan on taking it for another test tomorrow. I'd just replace it regardless, but not sure if I can find one around Seattle on a Saturday for a Perkins.
Another strange thing I can't explain, the gauge on the dash shows for Port engine shows 12 volts when running, but the DC panel shows 16. Still trying to figure out that one.
 
Sounds like port alternator may be fine but port regulator is likely bad? Is it an external regulator?
 
READY said:
Sounds like port alternator may be fine but port regulator is likely bad? Is it an external regulator?
Click to expand...
good call. Inverter overcharge shut off. What is the chance Starboard has the same reg that can be swapped to test theory.
 
Max Simmons said:
Headed out this morning for what was to be 5 days out on the hook. Leaving the marina, we turned on the inverter to keep the fridge running and charge a laptop. Inverter did not come on and the panel indicated "Fault". Voltage issue was indicated. At the DC panel, the voltmeter was showing 16 volts. I took the multimeter down and checked at the alternators. Port showed 16 Amps, Starboard shows 12.2 Amps.
Port alternator charges the house battery, which is what the inverter runs off of.
I shut down the Port engine and read DC panel with only Starboard engine running, voltmeter shows a little over 12V.
Shut down Starboard and run Port only, DC panel shows 16 volt.
I figure that the Port alternator is toast so return to port, pull alternator and take it to the local shop for testing. They put it on the tester and run it through the paces and say it's fine. Suggest that I check the sense wire to see if it is showing a drop in voltage. I went back, reinstalled the alternator and checked the sense wire, it shows 12.1 volt, while the output continues to show 16 volts.
Right now I'm questioning the shops testing. They said that it was showing 14 volts that was good.
Maybe voltage regulator is bad? I plan on taking it for another test tomorrow. I'd just replace it regardless, but not sure if I can find one around Seattle on a Saturday for a Perkins.
Another strange thing I can't explain, the gauge on the dash shows for Port engine shows 12 volts when running, but the DC panel shows 16. Still trying to figure out that one.
Click to expand...
Just for info, our fridges, freezers are all Danfoss/Secop auto changeover from 12v to 240v and if you look on Amazon you can get a 12v cig lighter charger for your laptop so you don't need the inverter on all the time. We use a UK firm (ADVERC) alternator controller and haven't had a problem in 15 years (with this boat) cruising.
We only use our3 KW inverter for the washing machine and dishwasher, it's turned off otherwise.
Just a different approach
 
With the boat shut down and batteries reading 12V, does the inverter now work, or is there still a fault?

Is there any way to get more info about the fault? Blinking LEDs or some other code, perhaps?

Two meters that disagree suggests its a metering problem, not really something in the alternator. Do you have a handheld meter that you can use to verify voltages?

Also check fuses for the alternator that charged the house bank.
 
twistedtree said:
With the boat shut down and batteries reading 12V, does the inverter now work, or is there still a fault?

Is there any way to get more info about the fault? Blinking LEDs or some other code, perhaps?

Two meters that disagree suggests its a metering problem, not really something in the alternator. Do you have a handheld meter that you can use to verify voltages?

Also check fuses for the alternator that charged the house bank.
Click to expand...
When shut down, no fault indicated and inverter works.
It would also work when at idle, but go into fault at higher RPM's which makes me think voltage regulator.
I've been verifying voltage with a Fluke digital handheld meter.
I have not seen an external voltage regulator, so assuming it is internal.
I have also not been able to determine the make or model of the alternator.
 
I recently installed a new Balmar 170 amp alternator and a wakespeed external regulator. About $1.5k for the parts but a fantastic combination. Very easy to monitor and troubleshoot on my Victron panel and phone.

Bonus is the balmar has an internal regulator as a backup if needed.
 
Your symptoms seem to indicate that the alternator is not connected to the house battery.

Have you checked the fuses as TT noted a few posts ago?

Check continuity of the wire from alternator to house battery.
 
I did check wire running to house battery and it is good.
This morning I swapped alternator from starboard engine, both engines rotate same direction. Everything works correctly. Voltage at DC panel just above 12v.
 
Max Simmons said:
I did check wire running to house battery and it is good.
This morning I swapped alternator from starboard engine, both engines rotate same direction. Everything works correctly. Voltage at DC panel just above 12v.
Click to expand...
So it is the alternator. Go embarrass the guys that said it was good and at the least get your money back if you paid for their opinion.
 
If “Everything works correctly” how can the shop guys be embarrassed, they already said it works correctly?

If it works, how can it be the alternator?

If this was my system unless I had a 70% +/- depleted FLA bank, I would not be happy with a charging voltage of “just above 12 V.”
 
OK, here's an update. The local shop had a replacement alternator that I picked up Monday. I moved starboard alternator back and installed the new unit. Started up and ran it for a few minutes. When I raised the RPM's the voltage started going up over 15v and monitor went into fault. Why this did not happen with the swapped starboard alt, I do not know.
I stopped by the local marina electrical shop and chatted with the owner about getting someone by to check it out. Maybe towards the end of September.
He suggested that I replace the sense wire, which I did.
I should also add that the sense wire, tach and key switch connection all are attached to the alternator by separate plugs.
When I run the engine with just the sense wire attached, alt puts out 13-14 volts. When I plug tach and starter switch connections, it goes back up to 15-16 volt charge. After some head scratching, I checked these connections for voltage and continuity. The tach lead had no voltage but continuity checked out. The key switch should show 12v when the key is turned on (verified on starboard engine) but on port, no voltage. So, right now I'm thinking that the fact the key switch circuit is not energizing, this must have something to do with the over-charging.
Question, what is the purpose of the energized circuit to the alternator? I can't find anything in my Perkins manuals and it isn't shown on electrical diagrams that I have been able to find on-line.
Sorry for this long yarn, but I am stumped.
 
When I run the engine with just the sense wire attached, alt puts out 13-14 volts. When I plug tach and starter switch connections, it goes back up to 15-16 volt charge. After some head scratching, I checked these connections for voltage and continuity. The tach lead had no voltage but continuity checked out. The key switch should show 12v when the key is turned on (verified on starboard engine) but on port, no voltage. So, right now I'm thinking that the fact the key switch circuit is not energizing, this must have something to do with the over-charging.
Click to expand...
The sense wire tells ALT there is something to charge.

I am scratching my head wondering why when tach and starter lead is disconnected it is charging within parameters.
Have you pulled the start switch wire, left tach connected and ran a 12v + to the ALT in same plug? Wondering if the start switch wire is grounded.
 
Just terminology, I think, but is the "starter switch" connection and "ignition" connection, which on a diesel is the the on/off key switch? I'm assuming it is, and as you surmised it should have 12V with key on, and 0V with key off. This signal is used to turn the regulator on/off so it's not drawing power when the key is off.

That said, not all alternators require an ignition signal and are instead capable of turning on/off on their own. In your case, it sounds like the alternator is using that signal as a voltage sense. Seeing no voltage, the alternator just keeps outputting current. Fix the ignition signal and it should all work correctly.
 
Max Simmons said:
Headed out this morning for what was to be 5 days out on the hook. Leaving the marina, we turned on the inverter to keep the fridge running and charge a laptop. Inverter did not come on and the panel indicated "Fault". Voltage issue was indicated. At the DC panel, the voltmeter was showing 16 volts. I took the multimeter down and checked at the alternators. Port showed 16 Amps, Starboard shows 12.2 Amps.
Port alternator charges the house battery, which is what the inverter runs off of.
I shut down the Port engine and read DC panel with only Starboard engine running, voltmeter shows a little over 12V.
Shut down Starboard and run Port only, DC panel shows 16 volt.
I figure that the Port alternator is toast so return to port, pull alternator and take it to the local shop for testing. They put it on the tester and run it through the paces and say it's fine. Suggest that I check the sense wire to see if it is showing a drop in voltage. I went back, reinstalled the alternator and checked the sense wire, it shows 12.1 volt, while the output continues to show 16 volts.
Right now I'm questioning the shops testing. They said that it was showing 14 volts that was good.
Maybe voltage regulator is bad? I plan on taking it for another test tomorrow. I'd just replace it regardless, but not sure if I can find one around Seattle on a Saturday for a Perkins.
Another strange thing I can't explain, the gauge on the dash shows for Port engine shows 12 volts when running, but the DC panel shows 16. Still trying to figure out that one.
Click to expand...
Is it possible/feasible to swap the alternators to see if the problem follows?
 
I replaced the "exciter" wire and all appears to be working OK. Hoping to get away for a few days this weekend and put it to the test.
 
Max Simmons said:
I replaced the "exciter" wire and all appears to be working OK. Hoping to get away for a few days this weekend and put it to the test.
Click to expand...

Was gonna suggest that the 12.1 volts on the exciter was the issue. It should be the close to the same as the alternator output as it's typically used as the reference voltage for the regulator.
 
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