Pulley size question

Classic Goldwings

Help Support Classic Goldwings:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

blfd04

Member
Joined
Jul 31, 2016
Messages
19
Reaction score
0
Location
Wanaque,NJ
Evening all
I have a question about the size of the crank pulley on the alt conversions.
My son is an apprentice machinist, he has a piece of stock that has been gathering dust in his shop for a while now. The issue is he says he could definitely get a 3 1/2" pulley, but his boss says he could possibly get one that is 3 5/8". Since I am not a math person, would there be a huge difference in voltage if the 91 metro alternator is used with the smaller crank pulley. I have no extras on my ride, and the only thing I plan to add is a set of driving/fog lights.
 
What I found was at a 2 to 1 speed ratio, with a 2" pulley on the alternator, you'll get 13-1/2 to 14-1/2 volts at idle. When I tried a smaller on the crank (3" I think it was) I got about 12-1/2 volts at idle. Around town the battery would loose charge from a fully charged state. With a lot of stops and starts the battery would get drained quite a bit.
To answer your question I think 3-5/8 should be ok.
 
As Dan said 2-1 or better. :yes:
The greater the ratio the sooner you reach full output on the alternator.
 
The voltages we are talking about are at idle correct? So in a perfect world as long as there is 12v at the battery it should maintain the battery voltage. I know that the headlight draws as soon as the key is turned, but I don't usually sit and idle for long periods of time,basically just in the morning when it is cold. As soon as you start riding the rpm's come up and it should be charging at that point. I don't use anything but the headlight, no radio,or extra lights, so in my case as long as I made sure I had the headlight draw covered a smaller one would work in theory correct?
Sorry I am being so dense at the moment, it happens more often than I care to admit lately, guess I'm showing my age and stubbornness.

Thank you
John
 
Y'all don't have to respond to my last post, the hamster finally got up to speed on the wheel and the lights came on :nea:
I was thinking in Volts not amps, which is why I went dense for a moment.
 
True anything over 12 volts at idle should be okay as long as you normally run above idle.
In my case around town especially when hot weather with fan running it wouldn't be good enough marginal, and I like knowing the battery isn't being constantly drained and charged.
Nice too not having to put a charger on at night to top up the battery.
 
Top