One Alternator won't charge

[Robin2]

I have a Sterling Alternator to Battery Charger (ABC) for a couple of years and I have both alternators (identical 70 amp) connected together at the B+ terminal on the auxiliary Alternator (Alt . This has worked fine until recently when I noticed the low charge warning light glowing for Alt A. I tested the combined output by switching on my microwave and there was a much higher than usual current draw from the battery.

 

This morning I disconnected Alt B and then Alt A appeared to work perfectly (normal charging amps into battery).

 

Has anyone come across this before, or have any ideas what the problem might be?

[bottle]

No expert but if AltA works and AltB works, each on their own, it will probably be the Sterling.

 

Check and clean all terminations first.

[Robin2]

No expert but if AltA works and AltB works, each on their own, it will probably be the Sterling.

 

Because the alternators are connected together before the Sterling I don't think it can be the problem

 

Check and clean all terminations first.

 

Grandmothers and eggs comes to mind ...

 

 

After further examination I think the problem may be in what I thought was the good alternator (Alt B ). At the moment I have it disconnected from the boat charging system and just supplying a 12v bulb. The voltage is only 12.2v even when I rev the engine.

 

On the other hand the voltage from Alt A is 13.84 when I rev the engine. And the low charge warning light is not glowing.

 

However when I temporarily connect the output of Alt B to the charging system the low charge warning light for Alt A glows.

 

All advice welcome.

Edited February 16, 2011 by Robin2

[ditchcrawler]

Because the alternators are connected together before the Sterling I don't think it can be the problem

 

 

 

Grandmothers and eggs comes to mind ...

 

 

After further examination I think the problem may be in what I thought was the good alternator (Alt B ). At the moment I have it disconnected from the boat charging system and just supplying a 12v bulb. The voltage is only 12.2v even when I rev the engine.

 

On the other hand the voltage from Alt A is 13.84 when I rev the engine. And the low charge warning light is not glowing.

 

However when I temporarily connect the output of Alt B to the charging system the low charge warning light for Alt A glows.

 

All advice welcome.

I am not saying in case you have already tried it.

[Sir Nibble]

Alt b is clearly u/s. I suspect a failed +ve dode but would need to test it to be sure.

[bottle]

Because the alternators are connected together before the Sterling I don't think it can be the problem

 

 

See told you I was no expert but read what I said. By a process of elimination you have found the problem.

 

 

Grandmothers and eggs comes to mind ...

 

 

 

Did you miss the smilie....

 

All advice welcome.

 

Is it ?

[pistnbroke]

correct diagnosis a glowing Warning light or Indicator light shows faulty diodes are the fault ...ps its not a low charge light when its out it indicates battery and alternator are connected ....

 

Worth checking the brushes and slip rings for wear while you are in there ..if one alternator is worn check the other

Edited February 17, 2011 by pistnbroke

[Sir Nibble]

ps its not a low charge light when its out it indicates battery and alternator are connected ....

 

 

In dynamo mode today are we?

[Tony Brooks]

correct diagnosis a glowing Warning light or Indicator light shows faulty diodes are the fault ...ps its not a low charge light when its out it indicates battery and alternator are connected ....

 

Worth checking the brushes and slip rings for wear while you are in there ..if one alternator is worn check the other

 

 

Not quiet true.

 

A glowing warning lamp means there is a voltage difference across it and although on a typical diesel inland boat it most probably does indicate an alternator fault if the boat has bilge blowers etc. controlled by the ignition switch it could just as well be voltdrop across the ignition switch or even poor ignition switch connections.

 

I'm still trying to work out why it can not simply be well charged batteries allowing the charging voltage to rise so the alternator with the lower set regulator shuts down. However the microwave test probably rules that out.

[Robin2]

I got a new rectifier on Ebay (£9.50 + postage) and now everything is working properly again. Indeed I think it is better than before so the fault may have been there for some time in a less acute form.

[Sir Nibble]

I got a new rectifier on Ebay (£9.50 + postage) and now everything is working properly again. Indeed I think it is better than before so the fault may have been there for some time in a less acute form.

Result.