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  #1  
Old 06-13-2018, 11:21 PM
RandyAB RandyAB is offline
 
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Default Alternator pulley ratio

Can anybody tell me what the pulley ratio would be for an IO540 coupled with a B&C 60amp 460 main alternator? Also, can somebody confirm that the vacuum pad will spin the backup alternator (B&C 462) at 1.3:1? I'm trying to confirm how much amperage to expect from each, particularly the main.
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  #2  
Old 06-14-2018, 07:50 AM
lr172 lr172 is online now
 
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Quote:
Originally Posted by RandyAB View Post
Can anybody tell me what the pulley ratio would be for an IO540 coupled with a B&C 60amp 460 main alternator? Also, can somebody confirm that the vacuum pad will spin the backup alternator (B&C 462) at 1.3:1? I'm trying to confirm how much amperage to expect from each, particularly the main.
There are several pulley ratio calculators online. Just use the outside diameter of each of the two pulleys.

Larry
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  #3  
Old 06-14-2018, 07:58 AM
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I beleive 3.8 is the correct ratio for most alternators with the large lyc pully.
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  #4  
Old 06-14-2018, 09:10 AM
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Toobuilder Toobuilder is offline
 
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Quote:
Originally Posted by RandyAB View Post
Can anybody tell me what the pulley ratio would be for an IO540 coupled with a B&C 60amp 460 main alternator?
Just as a point of reference from another thread of mine:

... if we take the typical 3.25 overdrive ratio of the large Lycoming pulley (9.75/3.0), we see we are spinning the alternator at almost 8800 RPM at takeoff....



To that end, Iíve added a 4.5 inch pulley to my alternator to slow it down. The resulting 2.16 ratio gives me a nice 5850 at takeoff and a comfortable 4750 at cruise
...

I have only ground run this setup and it seems to have no issue cranking out 40+ amps at 1000 RPM, so I think it will easily put out all I need in actual service
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  #5  
Old 06-14-2018, 09:35 AM
RandyAB RandyAB is offline
 
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Thanks guys. That alternator should more than handle the loads with those ratios.
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  #6  
Old 06-14-2018, 11:24 AM
lr172 lr172 is online now
 
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Quote:
Originally Posted by Toobuilder View Post
Just as a point of reference from another thread of mine:

... if we take the typical 3.25 overdrive ratio of the large Lycoming pulley (9.75/3.0), we see we are spinning the alternator at almost 8800 RPM at takeoff....



To that end, I’ve added a 4.5 inch pulley to my alternator to slow it down. The resulting 2.16 ratio gives me a nice 5850 at takeoff and a comfortable 4750 at cruise
...

I have only ground run this setup and it seems to have no issue cranking out 40+ amps at 1000 RPM, so I think it will easily put out all I need in actual service
I have the 7" pulley on my old narrow deck on the 6. I ended up with a ratio similar to yours. It performs well in all scenarios, except Idle (700 RPM) where the 50 amp alternator falls to about 20-25 amps. This is below my typical load at landing and get voltage warnings on short final as the speed bleeds off and the RPMs drop (FP). All in all, its not a problem.

Thought you might be interested and it's worth seeing what kind of fall off you have at 700.

Larry
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