More alternator questions

[Don Bradner]

You can spin an alternator at any RPM up to its max (8000 continuous on the
triple-nickels). Alternators vary in how much power they produce across the RPM
range.

Alternators made for heavy truck use have performance curves that give good
output at low RPMs. The 110-555JHO produces 50 amps at 1500, 100 amps at 2000,
and 140 amps at 3000. Full 160 amp production doesn't occur until 6000 RPM.

The rear, crank-driven alternator on mine has a pulley ratio of roughly 4:1
(hard place to get a measurement on the crank pulley). That would mean I should
get over 100 amps at idle. The front alternator is not crank driven, and the
pulley ratio is much smaller; I can only assume that the takeoff is rotating
faster than the crank.

I have seen no indication of tach/RPM problems, so I suspect the same pulley has
been used since the beginning. Alternators are sold without pulleys, normally,
so someone would have had to have gone out of their way to replace the original
one.

On 2/28/2007 at 4:18 PM Gregory OConnor wrote:

>Don, are all alternators designed to spin at the same RPM? if they
>are then swapping the same pully will do. I wonder if pully/alt
>swaps on BlueThunder in the past leave you with rpm issues? I'll try
>and measure my drive pully and alt pully today and post.
>GregoryO'Connor
>94ptRomolandCa


Don Bradner
90 PT40 "Blue Thunder"
Eureka, CA