I have a forklift with a Detroit Diesel 3-53 engine.

Unfortunately, the alternator on it does not charge at engine idle.

At idle it rotates at 1,250 RPM (measured with my tachometer).

If I push on gas, it charges.

This alternator is a rebuilt alternator.

Someone told me that I should change the regulator on this alternator
to make sure that it does charge at idle.

Could someone comment on this, and also how can I find different
regulators?

On a different forklift, I was able to solve it by making the pulley
diameter smaller, but here the pulley is already very small.

Thanks