Charging issues with Toyota style Denso Alternator

72bluNblu said
What electric fan?

It's a 2 speed fan out of a early 90's Volvo 940

The underdrive pulleys could definitely be an issue. Just because the alternator pulley is standard doesn’t mean much, it’s all about the ratio between the crank pulley and the alternator pulley. If that ratio isn’t stock or close to it, that could be the issue as the alternator will be spinning slower and you’d get a lower than rated output.

pishta said
your underdrive pulleys are working against the alternators RPM. Try a smaller pulley on the alternator. What is your estimated alternator shaft speed with your underdrive pulleys (OD of crank pulley / OD of alt pulley X RPM = shaft speed)

I looked into the pulley sizes & ratios and believe this is definitely the issue

Crank Pulley dia= 5.25"
Alt pulley dia= 2.63"
Ratio: 2:1

I looked again at the test report and they used a ratio of 3:1 (probably correct for a late 80's 4Runner). 80 amps @ 2500 RPMs (alt speed) / 3 (ratio) = 833 RPMs (Engine Speed).

With my actual pulley ratio of 2:1, at my idle speed I'm only pulling about 30 amps...

I'm not sure what the stock crank pulley OD is but bouchillon lists one with an OD of 7.375 and would get me to a ratio of 2.8. If my idle speed is around 900 RPM that should get back around 80 amps.