2007 Bavaria 50 Cruiser - Alternators Burn Out

[allendick]

The alternator on this boat have burned out multiple times, including before I bought it.

The boat is in charter and I have not been around when it happened but I am on board now.

In my experience with vehicles, putting in a larger battery can destroy the OEM alternator if the battery has gone flat and there are lots of accessories on when the driver tries to charge the battery after a jump start. The battery is like a dead short  and it seems the regulators do not limit current, so the alternator goes to maximum output and stays there until it burns out.  With the stock battery and few accessories on, I guess that the battery soon offers resistance and slows the charge rate, saving the alternator.

All that is a long way of saying that I had assumed the boat had a smart regulator, but appears to have the stock Volvo set-up with an internal regulator that senses from the yellow wire to the house battery.  After the last replacement the tech reported a steady output of 85 amps, which in my experience is about double what a 100 amp alternator can put out continuously without overheating.

The problem, I am guessing is the eight batteries (see image). They have no labels so I don't know what they are, but I am guessing that they offer very little resistance when run down and have destroyed several alternators.  Anyone know?

This boat has a lot of interior halogen lights and I am sure clients run the batteries down with the lights, if not by sailing on autopilot until the autopilot quits from low voltage.  Or both.

They then try to charge on the engine, possible with all lights on, and blow the alternator.

We had a little 110V generator on board to use to keep the batteries up, but it disappeared.  I'm getting another (the charger only draws 850 watts).

All this is a long way of asking what others have learned and if there is a good proven smart regulator I should install or an easy way to limit the internal one.

[allendick]

The alternator on this boat have burned out multiple times, including before I bought it.

The boat is in charter and I have not been around when it happened but I am on board now.

In my experience with vehicles, putting in a larger battery can destroy the OEM alternator if the battery has gone flat and there are lots of accessories on when the driver tries to charge the battery after a jump start. The battery is like a dead short  and it seems the regulators do not limit current, so the alternator goes to maximum output and stays there until it burns out.  With the stock battery and few accessories on, I guess that the battery soon offers resistance and slows the charge rate, saving the alternator.

All that is a long way of saying that I had assumed the boat had a smart regulator, but appears to have the stock Volvo set-up with an internal regulator that senses from the yellow wire to the house battery.  After the last replacement the tech reported a steady output of 85 amps, which in my experience is about double what a 100 amp alternator can put out continuously without overheating.

The problem, I am guessing is the eight red unlabeled batteries (anyone recognise them). They have no labels so I don't know what they are, but I am guessing that they offer very little resistance when run down and have destroyed several alternators.  Anyone know?

This boat has a lot of interior halogen lights and I am sure clients run the batteries down with the lights, if not by sailing on autopilot until the autopilot quits from low voltage.  Or both.

They then try to charge on the engine, possible with all lights on, and blow the alternator.

We had a little 110V generator on board to use to keep the batteries up, but it disappeared.  I'm getting another (the charger only draws 850 watts).

All this is a long way of asking what others have learned and if there is a good proven smart regulator I should install or an easy way to limit the internal one.

[Yngmar]

Sounds like you need a smart regulator with thermal management. With those, a probe is mounted externally on the alternator which senses temperature and shuts off charging when it gets too hot until it can cool down again. Most of the smart regulators on the market have this, including the Balmar MaxCharge and the Sterling Pro Reg DW. The Sterling is probably my recommendation as it's easy to retrofit on stock alternators and can work with the built-in regulator in place, which means you don't have to modify the alternator itself.

[allendick]

Thanks.  I'll look into this. I don't want to have to do a lot of modification, so if I don't have to mess with the alternator so much the better.

I have the Balmar on another boat and it works well.  I had an earlier Sterling and liked it so I'll check it out.

[tiger79]

The Sterling is probably my recommendation as it's easy to retrofit on stock alternators and can work with the built-in regulator in place, which means you don't have to modify the alternator itself.

Note that if used in conjunction with the alternator's built-in regulator, the Sterling can only increase the charge current, not decrease it.  For proper functionality, it should be installed as a stand-alone regulator.

[allendick]

Thanks.  I'm looking into this now and that is a good point since overcurrent is what I assume killed previous alternators.

I'm assuming that a new regulator is the only answer?  I recall on motorhomes, a simple self resetting breaker was used but I also assume there was an alternate path for the output so the alternator did not suddenly see an open circuit and blow diodes.

[tiger79]

If you use a decent stand-alone regulator, it will reduce the alternator's output if the alternator temperature gets too high.

[allendick]

Yeah.  I'll need a bolt-on temp sensor on the alternator, though, I think.  Otherwise it has no way to know. 

The max output can be programmed in on my Balmar reg as I recall to protect the belt(s), but how does it know the current, I wonder.

I've used a remote reading UR thermometer to monitor an alternator and it is very instructive. Left to themselves with empty batteries, they seem intent on self-destruction.

Does anyone know what those red batteries are?

[tiger79]

The Sterling Pro Reg DW comes complete with 2 temperature sensors.

The red batteries are presumably unbranded AGMs.