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Old 05-01-2011, 05:57   #1
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Marine or Automotive Alternator ?

How important is it to fit a marine alternator or will an automotive one be OK?
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Old 05-01-2011, 06:17   #2
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Automotive alternators are fine for a diesel. For a gasoline engine, you need the screens to stop sparks from triggering an explosion. I've used Delco rebuilds from the auto parts stores for 20 years and many thousands of hours. Specifically, I use a 17si frame, which I rewire for an external regulator (easy enough to do). I've added a 200 amp stator from Holcombe Armature (also easy). This gives you a 200 amp alternator for around $200. I keep one on the engine and one in the spares locker, just in case.
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Old 05-01-2011, 06:17   #3
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How important is it to fit a marine alternator or will an automotive one be OK?
Very important with an inboard gas motor. Not important with a diesel. Whether you are charging a big house battery bank or not will be a much bigger factor as an external regulator can make an alternator much more efficient for that purpose. I use standard 150 amp Delco truck alternators on my boat.

Lots of good threads in the "search" section.

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Old 05-01-2011, 06:48   #4
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Further Information.
My engine is a Ford 1.8 XLD (diesel) and the boat's hull is steel.
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Old 05-01-2011, 08:40   #5
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Further Information.
My engine is a Ford 1.8 XLD (diesel) and the boat's hull is steel.
Is there something wrong with your current alternator? Most alternators can be rebuilt to all but brand new condition for a fraction of the price of a new alternator. Most medium size cities will have a company who specializes in alternator and starter rebuilding.

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Old 05-01-2011, 12:10   #6
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Is there something wrong with your current alternator? Most alternators can be rebuilt to all but brand new condition for a fraction of the price of a new alternator. Most medium size cities will have a company who specializes in alternator and starter rebuilding.

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I have never used either of the two 70amp automotive alternators that I have (came with 2 engines I bought). I don't have an broken one but the previous owner of one of them suggested that we get something better.
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Old 05-01-2011, 12:56   #7
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There are 1000 of alt for sake on ebay I bought a rebuilt large frame leeseneville 105 amp for $45
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Old 05-01-2011, 13:21   #8
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I have never used either of the two 70amp automotive alternators that I have (came with 2 engines I bought). I don't have an broken one but the previous owner of one of them suggested that we get something better.
If you are saying that you have 2 automotive alternators that you want to try, go ahead. As long as the brackets and belt all line up correctly and wiring is correct, shouldn't be a problem. Make sure the fan on the alternator is tuning in the correct orientation with the motor so that the alternator is properly cooled when it spins.

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Old 05-01-2011, 16:30   #9
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Automotive alternators lack the fire (spark) screens and typically lack adequate cooling for marine use. They are designed to be cooled at idle by their fan, but to be cooled by the air rushing under the hood at operating speeds. So in a marine installation you may need a dual fan, or a blower or ducting to add cooling during prolonged operation. With a diesel and adequate cooling, "automotive" should be just fine, although diesel vapor CAN ignite, so spark arresting is never a bad idea.

"Most alternators can be rebuilt " Yes, but rebuilding is how you limp home. In the alternator trade, "rebuilt" means "fixed it". What you really want is a remanufactured alternator, which means they tore it down to the bare frame and actually tested each component to make sure it is within spec for a new part--not just operational and worn. Don't ask me how many years it took before I learned that.<G>
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Old 05-01-2011, 18:40   #10
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"Most alternators can be rebuilt " Yes, but rebuilding is how you limp home. In the alternator trade, "rebuilt" means "fixed it". What you really want is a remanufactured alternator, which means they tore it down to the bare frame and actually tested each component to make sure it is within spec for a new part--not just operational and worn. Don't ask me how many years it took before I learned that.<G>
Sorry your experience has been poor with the local service guy "repairing" your alternator. Rebuilding and remanufacturing are synonymous terms with reputable alternator / starter rebuilding businesses.

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Old 06-01-2011, 03:22   #11
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There are 1000 of alt for sake on ebay I bought a rebuilt large frame leeseneville 105 amp for $45
Is a 70 amp automotive alternator even powerful enough? - none of the posters has mentioned anything that small.
I don't want to 'make do and mend' with my alternators. I want one that will do a proper job. I'm installing the engine from scratch. It would seem a false economy to put in a poor alternator to start with.
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Old 06-01-2011, 05:32   #12
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It depends on the size of your battery bank Even when my batteries are low I do see 105 amps but never for very long as it tapers off fast
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Old 06-01-2011, 06:55   #13
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Is a 70 amp automotive alternator even powerful enough? - none of the posters has mentioned anything that small.
I don't want to 'make do and mend' with my alternators. I want one that will do a proper job. I'm installing the engine from scratch. It would seem a false economy to put in a poor alternator to start with.
Depends on the size of your battery bank, whether sail or power boat, your own daily "power budget", and type of batteries (e.g. AGM or flooded cell). AGM batteries have a higher charge acceptance rate and can take better advantage of a larger alternator. Charge rate tapers down as the battery voltage rises, so even a larger alternator will rarely be able to put out its full capacity. A sailboat will need a bigger alternator because (generally) the engine doesn't run constantly so recharge needs to happen as quickly as possible.

I have a little over 400 AH with all my flooded cell batteries combined, yet I'm using a "stock" 60A alternator. That's a little undersized but it just takes longer to do the job. I have a sailboat so the alternator is just used to keep the start battery up and augment other charging sources for the house bank (solar). Because my batteries rarely discharge below 75-80%, the alternator is not putting out its full capacity and is usually at less than 35A. Your situation will be different.
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