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Old 06-17-2010, 08:40 PM   #1
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How do I determine my alternator size?

I'm shopping for an isolator for my battery systems,and they all need to be sized according to the alternator amperage.My alternator doesn't have a tag on the outside,and actually looks as if it has been painted,possibly during a rebuild.Is there a way to tell,short of taking it to a starter shop,or is there a standard size I can guess it off at,and,if I'm wrong,will it hurt anything?It's a '96 Thomas with the 466 International,a marine house battery,and a very light electric load.If I guess,should I go with the larger isolator? What did you guys use?
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Old 06-17-2010, 09:16 PM   #2
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Re: How do I determine my alternator size?

Quote:
Originally Posted by Funkpirate
I'm shopping for an isolator for my battery systems,and they all need to be sized according to the alternator amperage.My alternator doesn't have a tag on the outside,and actually looks as if it has been painted,possibly during a rebuild.Is there a way to tell,short of taking it to a starter shop,or is there a standard size I can guess it off at,and,if I'm wrong,will it hurt anything?It's a '96 Thomas with the 466 International,a marine house battery,and a very light electric load.If I guess,should I go with the larger isolator? What did you guys use?
AutoZone should be able to help.
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Old 06-17-2010, 10:36 PM   #3
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Re: How do I determine my alternator size?

autozone often knows zero about bus parts, including alternators.

I do not think there is a good method to tell how many amps your alternator makes, especially if it has been rebuilt. Identical housings can be rated for different outputs..a standard leece neville can be as low as 105 amps, and as high as 300 amps or more. I think the low end of standard on a bus is 105 and less than 150. But that is just a general guestimate. Even if you find a tag, it might not be accurate. When you have an alt rebuilt, they often times can increase the output.

I know they cost a lot compared to a smaller one, but i think that you should prob go with at least 150 amp isolator. I installed an isolator once, all it did was kill my alternator in short order. could have just been coincidence. I would much rather have house and starting batteries together in series and not use an isolator at all. My favorite batteries are 8D truck batteries. A pair of these are really awesome. I prefer these batteries over any other lead acid batts for starting and for running items in the coach.
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Old 06-18-2010, 11:02 AM   #4
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Re: How do I determine my alternator size?

Quote:
Originally Posted by Smitty
Quote:
Originally Posted by M1031

AutoZone should be able to help.
This. When it comes to testing, doesn't matter if they know bus parts or not, all they need to know is how to operate the tester.

Smitty
That's right. The testing machine will (depending upon which model the store has) tell how much power is coming from the alternator. Considering the average personnel hired there, it's the machine that will give the answer.
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Old 06-18-2010, 11:22 AM   #5
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Re: How do I determine my alternator size?

I think the alternator in my International is larger than their machine.
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Old 06-18-2010, 09:06 PM   #6
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Re: How do I determine my alternator size?

i thought the OP did not want to remove his alternator from the bus.

Does autozone have a way to test the output of an alternator while it is still on the vehicle? or, if you have to remove the alternator and take it inside the store, can their machine handle a large bodied alternator like a leece neville? If the alternator fits on their machine, does it actually measure max output?
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Old 06-18-2010, 09:53 PM   #7
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Re: How do I determine my alternator size?

Quote:
I know they cost a lot compared to a smaller one, but i think that you should prob go with at least 150 amp isolator. I installed an isolator once, all it did was kill my alternator in short order. could have just been coincidence. I would much rather have house and starting batteries together in series and not use an isolator at all. My favorite batteries are 8D truck batteries. A pair of these are really awesome. I prefer these batteries over any other lead acid batts for starting and for running items in the coach.
In series,how can you prevent the house from draining the chassis batteries?

So,if undersizing the isolator will damage it,what will oversizing(within reason) do to the system? It can't damage the battery...

How did it kill your alternator?
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