Optimal 12V Alternator Speed for Diesel Engine Boat

In summary, the conversation discusses the search for the optimal speed to run a 12V alternator on a diesel boat engine. The individual has a feeling that the drive pulley is too large, causing the alternator to run slower than optimum. They ask for the speed range they should be aiming for and are directed to a website for Delco Remys 21SI Alternators Series. The conversation then turns to the diameter ratio needed for the alternator to rotate fast enough at normal running speed, with the individual mentioning their alternator brand and probable output. They plan to measure and potentially look for a smaller pulley at a breaker's.
  • #1
sophiecentaur
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I have looked all over in the search for the optimal speed to run a 12V alternator. I have a diesel engine on my boat which is never run above 2500 revs and I have a feeling that the drive pulley is too large - so the alternator runs slower than optimum.
Does anyone know the speed range that I should be aiming at for the alternator?
 
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  • #2
It would depend on what alternator you have. For Delco Remys 21SI Alternators Series, it would be in accordance to this:
21siAlternatorPCDelcoRemy.jpg

http://www.newindo.com/delcoremy/20si-21si-26si-delcoremy-generators.htm"
 
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  • #3
Thanks. That tells me that I should have around a 2:1 diameter ratio for the alternator to be rotating fast enough at normal running speed. From memory, the diameter of the existing alternator pulley is much more than half of the flywheel pulley so it looks as though I could do a lot better than at present. As the very maximum engine revs are 3k, it looks as if a 2:1 ratio would not over rev any of the alternators on those graphs. The make of my alternator is a Valeo, btw, but I'd bet the speed curves are much the same. It's 12V and probably a 40A max output (as are all the old ones) but I've never measured more than about 10A from it on my 'tong' meter. The warning beep only stops when the engine's doing over 1k.

I shall have to do some measuring when I'm next aboard and then look around for a smaller pulley at a breaker's.
Cheers.
 
  • #4
sophiecentaur said:
I shall have to do some measuring when I'm next aboard and then look around for a smaller pulley at a breaker's.
Cheers.
Go for it. :smile:
 

Related to Optimal 12V Alternator Speed for Diesel Engine Boat

1. What is the optimal speed for a 12V alternator on a diesel engine boat?

The optimal speed for a 12V alternator on a diesel engine boat is typically between 1200-1500 revolutions per minute (RPM). This speed allows the alternator to generate enough power to charge the battery and run any electrical equipment without putting too much strain on the engine.

2. How does the alternator speed affect the performance of a diesel engine boat?

The alternator speed directly affects the performance of a diesel engine boat as it determines the amount of electrical power being generated. If the alternator speed is too low, the battery may not receive enough charge and the engine may struggle to run any electrical equipment. On the other hand, if the alternator speed is too high, it can put excessive strain on the engine and potentially cause damage.

3. Can the optimal alternator speed vary for different types of diesel engines?

Yes, the optimal alternator speed can vary for different types of diesel engines. It is important to consult the manufacturer's guidelines for the specific engine and alternator combination to determine the optimal speed. Factors such as engine size, horsepower, and electrical load can also impact the optimal speed.

4. What happens if the alternator speed is set too low?

If the alternator speed is set too low, the battery may not receive enough charge and could eventually run out of power. This can result in the engine not starting or stalling, and also prevent any electrical equipment from functioning properly. In addition, a low alternator speed can cause premature wear and tear on the engine.

5. Is it possible to adjust the alternator speed on a diesel engine boat?

Yes, it is possible to adjust the alternator speed on a diesel engine boat. This can be done by changing the pulley size or using a voltage regulator to control the output of the alternator. However, it is important to consult a professional to ensure that the alternator speed is adjusted properly for optimal performance and to prevent any damage to the engine.

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