alternator conversion almost successful

karl f

Well-known Member
I completed converting our 400 to 12v w/ alternator. Had new brackets fabricated so it fits under the hood and uses the original belt.

The first alternator was a used freebie. would not charge. It had worked on the bench tester prior to my project but it did get rained on on accident.

the second alternator is store purchased but will not begin to charge until 3 notches from wide open on the throttle (around 1000 rpm). Even if you try to excite it with a jumper wire. once excited, it charges at all engine speeds.

I've double checked my wiring and it's correct. I thought the sealed warning lamp (not LED) was the culprit but the lack of excitement with a jumper wire seems to elminate that possibility. It's acting like a one wire!

The only other factor i can think of is the pulley size/alternator rpm. I am using a bigger pulley than a car. but it is smaller than the original adjustable generator pulley. i'll have to measure.

I assumed with the warning light setup that the alternator would become excited when energized regardless of rpm. Anyone else run into this before?

-karl f
 
There are literally dozens of different regulators that can be used in the 10SI series of alternators. Some of them use an AC signal to excite the regulator to energize the field coil. With those regulators the diode trio, if used, is used only to provide voltage to turn off the light. Applying voltage to that terminal ( number 1) will not excite the regulator. Also, the number 2 terminal may have no connection inside the regulator. All voltage sensing is done internally in the regulator.
 
the pulley is 3 inches. And i forgot to say it was a 10si alternator.

rough calculations and quick measurements indicate at
500 engine rpm = 975 alt rpm
800 eng rpm = 1560 alt rpm
1000 eng rpm = 1950 alt rpm
1500 eng rpm = 2925 alt rpm
1600 eng rpm = 3120 alt rpm

looks like this particular version needs to spin around 2000 rpm to excite.

I may get my core back then talk to the alternator shop and get the right regulator to make that one work for my needs.

-karl f
 
You know, that's exactly how the alternator on my Super H works.

I never considered it a problem. My idiot light is an LED, BTW.

Consider that a typical car/truck engine idles at 750-1000 RPM, and the crank pulley is driving the alternator at better than 2:1 ratio.

The alternator is spinning at around 2000RPM at idle on a car or truck.
 

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