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Old 13-01-2010, 21:38   #1
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Alternator Fluctuating Voltage

Recently I started the diesel (volvo d2-55) and got a battery warning. The alternator (standard 60Amp) was putting 13V out on the engine display when normally it's 14V (ALWAYS). When I idled to 2000rpm the output rose to 16V. I have a 3x4d gel house bank (550Ah) and 1x4d gel start batt, so I shut down for fear of flying the batteries.

I'm guessing the internal regulator is shot, hence the varied V output???
The Link 2000 was showing 0-30 amps jumping all over the place (usually it's 60).

The boat is relatively new to me and I'm still learning the systems, like how exactly are my batteries charged but here is what I know. From the alternator the + runs to a split, from which it goes to the Start batt, and to the inverter (then to the xantrex 110V charger??? for the house batteries)
Everything has been working well so far, and I've never really had a problem with the batteries but I also never had to charge the batteries via the Diesel.

I'm now faced with what to buy;
- new internal regulator -$280 from Volvo
- New external regulator - $300 form Bomar (can I hook it up to the old alternator???)
- new HO alternator with ext. regulator - $800

I'm planning on cruising the boat for a month in may, and would like to be self sufficient on power (ie. no portable generator if I can help it and I have no solar/wind)

Also, had this happened on the water and I needed to motor for an extended period, what should I do? disconnecting the alternator is the best idea but how to do it without frying anything?

thanks
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Old 14-01-2010, 00:18   #2
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With higher voltage at lower RPM would sound like the alternator brushes might be getting short and arcing. You may need new ones.

Next test the batteries! An over charge can be caused by a battery demand. If it's shorting out then it acts like a carbon pile. How old are the batteries and how long had they been sitting?

Also check for a short in the wiring, that can cause a demand on the alt.

Then goto the regulator.
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Old 14-01-2010, 04:58   #3
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Id take the alternator to a good alternator shop, with marine experience (if possible).

Masco wants $360 for an Alternator for the D2:
Alternator for VOLVO PENTA D1, D2, D4, D6 Series Diesel Engines
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Old 14-01-2010, 06:13   #4
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Disconnect and test batteries individually 1st. Correct as necessary.
General charging voltage should maintain 13.8-14.2 volts at all time. Your voltages out of whack indicate a voltage regulator problem. A scope is necessary to diagnose bad diodes.
As suggested, if the batteries are in order get it rebuilt and be done with it. $800 for a new one? I'd never.....
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Old 14-01-2010, 06:24   #5
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$800 for a new one ... funny that as soon as you mention the word boat the price seems to double ..
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Old 14-01-2010, 07:12   #6
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Quote:
Originally Posted by delmarrey View Post
With higher voltage at lower RPM would sound like the alternator brushes might be getting short and arcing. You may need new ones.

Next test the batteries! An over charge can be caused by a battery demand. If it's shorting out then it acts like a carbon pile. How old are the batteries and how long had they been sitting?

Also check for a short in the wiring, that can cause a demand on the alt.

Then goto the regulator.
The voltage is low (13V) at low rpm. only goes up when i increase throttle (2000rpm - 16V)

Batteries look ok, 13.1v base on the start and same on the house.

The batteries are 2004 and i use 10-50% once a week. at all other times they are on float via xantrax and link 2000.
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Old 14-01-2010, 07:15   #7
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Originally Posted by GordMay View Post
Id take the alternator to a good alternator shop, with marine experience (if possible).

Masco wants $360 for an Alternator for the D2:
Alternator for VOLVO PENTA D1, D2, D4, D6 Series Diesel Engines

yes. thanks. the 800$ is for a 100amp balmar alternator with external (and internal - disconnected) regulator. This might be a good way to go seeing as it will be less stress on alternator when charging.
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Old 14-01-2010, 07:37   #8
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Here is a battery system diagram (in reverse... ?!?)
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Old 14-01-2010, 10:15   #9
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Quote:
Originally Posted by wrublewski View Post
The voltage is low (13V) at low rpm. only goes up when i increase throttle (2000rpm - 16V)

Batteries look ok, 13.1v base on the start and same on the house.

The batteries are 2004 and i use 10-50% once a week. at all other times they are on float via xantrax and link 2000.
I got the impression otherwise.
Quote:
Originally Posted by wrublewski
The alternator (standard 60Amp) was putting 13V out on the engine display when normally it's 14V (ALWAYS). When I idled to 2000rpm the output rose to 16V.
So, that makes the batteries 5-6 years old. I think I'd be testing the batteries. And one should not drain the batteries below 75%, it shortens the life span more then recommended.
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