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Alternator failure - sudden or gradual?


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I am just looking for a very general opinion here - Do alternators generally fail rapidly or do they tend to die gradually?

 

I am getting very poor battery charging from mine - but not none. So I am trying to decide if I should replace the alternator or search for a problem somewhere else. 

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2 minutes ago, WJM said:

Ok, so failure is not a binary condition? As the brushes wear they alternator produces less charge? 

 

Only when they make intermittent contact or are so worn it creates resistance between brushes and slip rings.

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12 hours ago, WJM said:

No flickering that I can see. Though the red light marked AUX is illuminated.

 

 

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The AUX light is the warning light for the domestic alternator. It should not be illuminated when the engine is running. If it is, it is telling you that the alternator is faulty (or maybe a wiring issue).

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With a vehicle we had the regulator on the back of the alternator fail and would randomly decide that 10-11v was fully charged, hard to diagnose since there were never any warning lights as the alternator was working and of course when checked with a meter it was at times when it was putting out it's full voltage (night time driving with headlights flicking between bright white & dim yellow was interesting, used to get flashed a lot when people assumed dip beam turning white was high beam going on).

Ended up doing a (temporary) frankenstein fix with a regulator from a completely different type of alternator, It was still frankensteined and working perfectly when we sold the vehicle 10 years later.

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3 hours ago, nicknorman said:

The AUX light is the warning light for the domestic alternator. It should not be illuminated when the engine is running. If it is, it is telling you that the alternator is faulty (or maybe a wiring issue).

Also slipping drive belt. Take a look with the engine running in the dark too. A faint flicker can be seen that might not be in daylight. Had this with a car once when the alternator was poorly.

Jen

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Another Alternator related question - what is the difference between a regular Alternator bought from a Motor Factors and one that has been 'Marinised'? 

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5 minutes ago, WJM said:

Another Alternator related question - what is the difference between a regular Alternator bought from a Motor Factors and one that has been 'Marinised'? 

 

For any given alternator model usually nothing but it may have a salt water resistant coat of paint.

 

A fully marine alternator should be insulated return so a "marine" regulator might have a negative wire whereas an automotive one may use the case. I am thinking Parris-Rhone as a possibility.

 

If you want a definitive answer you really need to specify the alternator makers and model number.

Edited by Tony Brooks
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16 minutes ago, WJM said:

Thanks Tony,

 

One more question. I have a 70amp Alternator - does it matter if I replace it with a 90amp?

 

Apart from one thing then no as long as it fits and the pulleys stay in line and have the same groove profile.

 

The one thing is that at 90 amps you are pushing it with a single V belt so make sure it's a quality make like Gates and ensure it's a notched one because   boats typically use the smallest pulley possible and the notches help it grip on small diameters.

 

If you intend to fit the old pulley onto the new alternator you need to ensure the shaft size is the same.

Edited by Tony Brooks
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1 hour ago, WJM said:

Another Alternator related question - what is the difference between a regular Alternator bought from a Motor Factors and one that has been 'Marinised'? 

A much bigger number on the price sticker! ?

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1 hour ago, Jen-in-Wellies said:

A much bigger number on the price sticker! ?

I took my 100 amp alternator into my local old fashioned repair man here in Lowestoft he looked at the 100 Amps stamped on the flange and said "someone is optimistic"

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