Alternator charging

[Campbell]

I have been having an issue with the 90a alternators I have charging.. I have the alternator going straight to the battery with no tie in to the oe wiring bundle. I have one alternator that works fine this way but my other ones won't kick on and charge. Someone mentioned that the alternators won't charge without the, grounding I guess, from the alternator light. Electrical stuff is not my forte - any suggestions on how to address this? thanks

[Flyinglizard]

Rev it over 4000 and see if starts humming. Most of the Bosch will self field over 4k .
If not, hook a key on hot wire/light, to the field post.

[Campbell]

Thanks Mike, but I don't understand what this means "If not, hook a key on hot wire/light, to the field post". These other alternators have rev'd up to 6000 and not kicked on - they each did once but not again. thanks

[T Broring]

We run a large green warning light on the dash for the alternator(red for oil pressure). We connect one side of the bulb to switched ignition-on power and the other side of the bulb to the field connector on the Bosch alternator. This field power supply should get the alternator charging once you exceed abour 1000 RPM. If the alternator fails the warning light will come on. I have seen GM and other alternators start charging themselves withour a field at the 4000 RPM Mike references. Not sure about Bosch. The issue is that with all the vibration and hard shut offs with the master switch, you could damage a diode or something else on an alternator. In some cases just the voltage regulator may need replacement. I would suggest that having a field connection is the safe setup. Also, the warning light setup is worth while because you will know what is going wrong if the motor starts acting up while on track.

[Sandro]

You need to have the blue wire coming out of the alternator connected to a light, can't just have it cut and dangling. Without that connected the alternator will not charge properly and you will damage the alternator diode.

When its connected, turn the ignition to the on position(don't start car), light should come on. Then start the car, and the light should still be on, rev the car passed about 1-2k and the light should go out. When its out, you know its charging and all is good.

I also would recommend getting a master power switch that uses a resistor to ground it when you flip the switch, as the voltage spike can destroy the alternators diode.

[Campbell]

Thanks, I take it from what you say I wire up a warning light with the blue wire off the alternator on one side and the other side to an ignition on power source.. do I have that right? again, not my forte!!

[Sandro]

correct

12v switched source --> light ---> blue alternator wire.

So when there is a voltage difference(alternator not charging) the light comes on.