Operating voltage low until reved up

[Earendil]

I can't really squeeze the entire issue into the title, so for everything that thinks they already know the answer, give me a second to explain :)

First of all, I have no idea how long this issue has existed, because the circumstances aren't normal for me.

1. Turn car on and let idle. Operating voltage is at 11.8 (way low)
2. Rev engine past 1500rpm. Voltage jumps to 13.9
3. Let engine fall back to idle. Voltage hovers around 13.78

I very rarely do anything but get in my car and go. But I was getting ready to change the oil and wanted to let her run for a few minutes. I noticed that battery light and did my checks. This was also reproducible 3 times in a row.

Now I know that the alternator really kicks in hard fast a certain RPM. But does it make sense that it would just not function at all until it's spun up the first time, and then it works fine at all RPMs?!

[Jalves619]

Mine has been doing this as well. When you started an older car with a single wire alternator you had to rev it to "excite" the alternator and get it to start charging. Newer alternators have wires specifically for this task, but for some reason, in our situation they aren't working. It's either something inside the Alt itself, or it's not getting the signal it needs. Sorry I don't have a very scientific explanation for you, or a solution for that matter. I've been lazy and just tapped the throttle when I go to warm up my car, rather than actually look into it further.

[Jalves619]

The wire supplying the field current is often referred to as the "exciter" wire. The drawback of this arrangement is that if the warning lamp burns out or the "exciter" wire is disconnected, no current reaches the field windings and the alternator will not generate power. Some warning indicator circuits are equipped with a resistor in parallel with the lamp that permit excitation current to flow if the warning lamp burns out. The driver should check that the warning indicator is on when the engine is stopped; otherwise, there might not be any indication of a failure of the belt which may also drive the cooling water pump. Some alternators will self-excite when the engine reaches at a certain speed.


Straight from the Alternator Wiki article

[Earendil]

Good info! I rarely look to Wikipedia for car advice, but this time it pans out. I'll have to check my wires, see if anything isn't obviously wrong. But if not, it's nice to know at least one person has lived with this issue for a while without perceptible harm!

[chucker]

http://www.davebarton.com/AdjustableVoltage.html

Try this.


chucker