Alternator not charging

[Sam the Sailor]

Yesterday after 2-3 hours of motoring the "battery not charging" warning light suddenly came on. Next day I measured the amps and noticed that the charger was able to charge the house bank only with 3-4 amps at 12.6 V. Before the warning light came on the alternator was outputting ~45 amps.

My 450 Ah battery bank was low (-200 Ah), so the alternator was running on full capacity that 2-3 hours. Thus my first suspect is that overheating damaged the alternator. If that's the case is there any means to test that before going to buy a new alternator?

The alternator is 50 amp and from -91, so is it possible that brushes have gone bad? Or could it be something else? The engine I have is Volvo Penta MD22.

I tried to disconnect the house bank and then the charger was able to (slowly) rise the already full starter battery voltage to 14.4V.

All advices highly appreciated!

Best,
Sam

[Empty Pockets]

Use a jumper to apply full battery voltage to the “field” post on your alternator and measure the output. If correct, your regulator is bad. If still not showing full output, the alternator is bad.

[SFH]

Hi Sam

Had the same problem a year ago. In my case it turned out to be a grounding issue. Probably due to vibrations I guess. After tightening it up alternator charged 100%.

Hope you get it solved

Steen

[GordMay]

Check out a blast from the distant past ➥ http://www.cruisersforum.com/forums/...sting-375.html

[Sam the Sailor]

Thanks for the comments! All the connections look fine, are tights and multimeter shows minimal resistance. Also when charging the voltage across the alternator and the battery is the same indicating no significant losses in cables. The only problem is that the amps are very low.

I couldn't find the field post from my alternator so couldn't try that test.

Today I noticed another thing: the engine hours in tachometer are not counted properly. The hour meter shows 6 hours from my last log entry, but in reality I have motored something like 12-15 hours during that time. The RPMs in the same meter are displayed correctly, though.

I think I need to get a professional to look at the alternator. Any brand suggestions if I have to buy a new one?

Thanks again!

Best,
Sam

[Lepke]

Most auto parts stores will test alternators. Ebay is probably the cheapest place to buy a replacement.

[Cat36Mahalo]

No tach is a sure sign the regulator is not working. It could be bad or you may not be sending any excite voltage to it.

[Empty Pockets]

How many wires on the back of your alternator?

[DeepFrz]

I would suggest that with that size battery bank that you buy at least a 100 amp alternator and de-rate it to about 80 amps. That way you won't need to upgrade your belt and pulley system. Of course you will need an external regulator capable of doing the de-rating.

[Gregjo]

Tacho is usually run off the sine wave (ac voltage) at the “star” point of three windings in the alternator, any alternator fault will affect this.
Send alternator number or picture of connections and we can come up with a test sequence.
Cheers Greg the sparky

[Gregjo]

And what Gord said!

[Sam the Sailor]

Originally Posted by Cat36Mahalo

No tach is a sure sign the regulator is not working. It could be bad or you may not be sending any excite voltage to it.

The tachometer is working, i.e. it is showing the correct RPMs. However the engine hours in the same gauge are not counted properly.

Originally Posted by Empty Pockets

How many wires on the back of your alternator?

There are five wires total:
B- to negative battery terminal
B+ to positive battery terminal (both house and start batteries through split diode)
W not sure where this goes, maybe to tachometer?
D+ not sure where this goes, maybe to tachometer?
Yellow wire with no letter coming directly from house battery. My understanding is that it is for voltage sensing to compensate wire and diode losses.

Br,
Sam

[Sam the Sailor]

Originally Posted by Gregjo

Tacho is usually run off the sine wave (ac voltage) at the “star” point of three windings in the alternator, any alternator fault will affect this.
Send alternator number or picture of connections and we can come up with a test sequence.
Cheers Greg the sparky

I couldn't find any numbers from the alternator, the only thing I found was text Valeo and I know it should be 50 amp alternator. Attached is the picture of the wiring.

Unfortunately I'm flying home tomorrow so I don't have much time to do testing before departure :/

Best,
Sam

[Sam the Sailor]

Originally Posted by DeepFrz

I would suggest that with that size battery bank that you buy at least a 100 amp alternator and de-rate it to about 80 amps. That way you won't need to upgrade your belt and pulley system. Of course you will need an external regulator capable of doing the de-rating.

Thanks for the advice in case I need to buy a new alternator!

Br,
Sam

[Gregjo]

A little hard to see from the photo, however...
W - yes tacho output
D+ - usually alternator/battery light (Charging voltage when running, ground when not charging)
Yellow wire - I am guessing but maybe either external battery sense or input to the field winding from a smart regulator

W = AC output should be 1/2 battery voltage if you measure DC volts ie. 7v
D+ = 0 volts stopped or not charging 14 volts if everything is well
Yellow wire = 0-14 volts if from a regulator depending on battery charge state

Measure and report back
Cheers Greg