Alternator robbing HP, what's the right idle? - Page 5 - SailNet Community
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post #41 of 44 Old 02-04-2020
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Re: Alternator robbing HP, what's the right idle?

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Originally Posted by Scottrgrewe View Post
Is this correct?
Do I NEED a new pulley?
If so, did I calculate correct size?
Where to buy?
Do the math for your max maintained RPM (motoring???) and the alt should be spinning at it rated max RPM... and then determine the diameter of the pulley you need. I am guessing is may be larger in the 4" range... You don't want the alt spinning too fast as you don't want your engine over it "red line"... The alt RPM is a ratio of the Flywheel crank circumference / alternator pulley circumference

Engine RPM / flywheel circum = alternator RPM / alt circum

You should know the MAX alternator RPM and so you SOLVE for the alternator circumference

so it might be

2,000/14 = 6,000/x

14/3 = +/- 4.5

if max alt speed is 6,500 for engine 2,000 RPM

If Alt RPM is higher alt pulley diameter would be LESS than 4.5"
.
The alt maker can supply you another pulley or perhaps a local alternator shop like Bronx Ignition... I can get one for you and ship it if you can't find it down there.

pay attention... someone's life depends on it
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post #42 of 44 Old 02-04-2020
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Re: Alternator robbing HP, what's the right idle?

I have got the same engine and flywheel.
If I try to charge at idle, the belt shows signs of dancing and distress.
Keep your revs up at high alternator amperages.
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post #43 of 44 Old 02-04-2020 Thread Starter
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Quote:
Originally Posted by Rockter View Post
I have got the same engine and flywheel.
If I try to charge at idle, the belt shows signs of dancing and distress.
Keep your revs up at high alternator amperages.
What size is your alt pulley? Is mine too small?
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Re: Alternator robbing HP, what's the right idle?

Quote:
Originally Posted by Scottrgrewe View Post
What size is your alt pulley? Is mine too small?
you want an ouside diameter for the pulley to be 4.5" - 4.75"

pay attention... someone's life depends on it
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