High output alternator

Carl · 03-23-2012, 06:34 PM

Added high output alternator and I now see headlights "surge" when at idle?

Is this normal?

Ford_6L_E350 · 03-23-2012, 06:58 PM

I wouldn't think that is 'normal'.

If the lights are changing intensity, the voltage is also changing.

Do you have a voltmeter to measure the voltage at the alternator? At idle it should be 13.6V or so and steady (unless you idle is also varying). It should go up to ~14.2V above idle and still steady.

Mike

**BroncoHauler** · 03-23-2012, 07:41 PM

Is it an internally regulated alternator, or externally regulated? Sounds like a voltage regulation issue.

Herb

Carl · 03-23-2012, 08:05 PM

voltmeter in cigarette lighter.

got in truck and it read just under 12

Once started and at idle it goes from 14 to 14.3
It is not steady, but goes 14, 14.1....14.2...14.3... etc....

headlights surge slightly at idle

thoughts?

Ford_6L_E350 · 03-24-2012, 09:40 AM

Bouncing around a couple of tenths of a volt is not uncommon. I'm surprised you can see that change in the headlights. What is the voltage change at the lights?

The battery should act as a big 'sink' and stabilize the voltage.

Mike

**daveb** · 03-25-2012, 12:01 PM

It sounds like part of the bridge rectifier is blown. I've had two different high amp alternators. One would vary between 13.2 to 13.9, never reaching the 14 zone but was all over the place voltage wise. The new one I have regulates between 14.1 and 14.4 and is much more steady. None of them have or had an affect on the headlights you are seeing. I'd check all the battery & connections then have a shop look at the alternator...sometimes you might get a bad product right out of the box.

jumpshowhigh · 04-09-2012, 12:17 AM

High output alternators are usually delta wound instead of wye wound in order to improve their higher amperage output, but higher current is achieved at the expense of low rpm voltage. Most manufactures will fit the alternator with a smaller diameter alternator pulley so the alternator does not fall below the cut-in voltage at idle but if it's right on the edge, you can get a "pulsing" of lights at idle. It's a function of the spacing between the rotor and stator and it's not harmful, just slightly annoying. If the pulsing stops when you increase the vehicle rpm's, and the voltage is normal, then the scenario likely as I've described and you can either live with it, swap to a smaller diameter pulley, or switch to a different alternator where the stator/rotor tolerance might be tighter.

Carl · 04-10-2012, 04:57 AM

Turned out that the pulsing was result of wiring run along side each other from alt to welder box, and battery to welder box, (25' from alt to box.) Once we seperated the wiring, no issue.

c7train · 04-10-2012, 08:54 AM

jumpshowhigh, it is clear you are an authoritative figure on this stuff. The smaller pulley will increase the production at lower RPM, can it harm things when heading down the highway or at higher RPM?
C.

jumpshowhigh · 04-10-2012, 09:19 AM

The bearings are typically rated for much higher rpm's than you could normally expect to hit so the answer is no, at highway speeds, the bearings should be fine.

Quote:

Originally Posted by c7train

jumpshowhigh, it is clear you are an authoritative figure on this stuff. The smaller pulley will increase the production at lower RPM, can it harm things when heading down the highway or at higher RPM?
C.