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Installed Denso alternator in my 2000 Toyota 4Runner with new drive belt. Set belt tension low, and got 13.1 volts from batt posts with engine running, then loaded it and volts remained steady @ 1500rpm. Tightened belt to max deflection 1/4″, which increased volts to 14.06 idle- 14.09 loaded. I was expecting a higher voltage of 14.5 or so from a remand alternator. :dry:
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With the system loaded 14.0 volts is bout all you’re gonna get. Some cars run as high as 15 volts and as low as 13.0 volts.
I agree. High beams, a/c on, radio on, and the revs ~1750; as long as you see at least 13.0 at the battery consistently and no more than 15.0 volts it’s okay. To be sure, check the output at the alternator and compare it to the battery for piece of mind. You shouldn’t be more than 0.5V off from each other. Also when rebuilt, the output is checked at the alt., not at the end of a cable, so you might be losing a few tenths.
The voltage isn’t the significant thing, the current is.
The voltage depends on the battery state of charge and its state of health.
The voltage will be lower if the battery is new and has low internal resistance. The only time the voltage will creep up is if the battery is getting old and sulphated and its internal resistance creeps up to a few tenths of an ohm.
So low voltage is a sign of battery health, not of alternator sickness.
You might want to put a clamp-on ammeter on the alternator to battery thick wire to monitor the current.
And of course the current will be low if the battery is well charged. Turn the headlights on for 10 minutes with the engine off, then try measuring the charging current, that will be a more realistic test.
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