Why does my voltage increase drastically, when the RPM's go up? Options

[highways]

Any ideas?

[smontanaro]

Voltage regulator gone bad maybe?

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[Spoke]

Check the belt on your alternator. If the belt is loose, this may be the issue.

If the belt on your alternator is not loose, it is possible that the brushes on the armature of your voltage regulator are dirty or worn out. This is an engine speed related issue and the only engine speed dependent electrical unit is the alternator.

I had a Dodge Colt in college that had the same issue. On a long distance trip, the voltage kept dropping lower and lower. I stopped to check belts and such and noticed at idle that the alternator was charging. Rev the engine and battery would discharge.

Took alternator apart and found that when I spun the alternator, the resistance across the armature (spinning part) would jump real high, then drop low when it stopped. The brushes were worn and dirty. I cleaned them and solved the problem. Alternator lasted another 4 years until I sold the car.

[highways]

Brand new voltage regulator from pelican. So... does that mean it doesn't work? Or the alternator has a funky diode?

Sorry... just saw the third post. I guess i need to try cleaning the brushes.

[SGB]

Don't drive far like this. Battery will boil over into the hell hole. VR is probable culprit, but it could also be the alternatore as well.

[purple]

Methinks you try the voltage regulator FIRST.

If the belt is loose, the voltage would go DOWN since the alternator would not be turning as fast as the engine, right?

If you replace the regulator and the voltage still gets wild, then the possibility would be your diodes.

Dirty brushes would also correlate to a DECREASE in voltage.

That's just my experience with 4 years of electrical engineering schoolwork. This car has a way of being ass-backwards at times, so i could be wrong.

[Spoke]

Big Duh for me on my first post. I was thinking it was a voltage decrease, not increase. I guess I should read all the words. I only finished 1/2 of my Eveline Woods speed reading course. Sometimes I wish the voltage on my car would increase; it always seems low.

Yep, increase with speed points to the VR.

[davep]

The alternator can produce more power as the RPM is increased.
As the output current increases the load on the battery decreases, thus the battery voltage goes up. Normal no-load battery voltage is 12.8 volts. Under load this can drop under 12 volts. The VR limits the charging voltage to about 14 volts. If you measure the battery voltage anywhere other than the battery posts the voltage will be less due to the resistance of the wiring between the measured points and the battery posts. The greater the current in the circuit, the greater the voltage drop.

If your voltage is going over 14 volts then the VR may be at fault.
If your voltage starts out at 12 volts and rises to 14 volts, then that is normal.
Measuring voltages in any system depends a lot on how the measurements are taken. It is never a trivial exercise. The idea of a 12 volt system in the 914 is really a misnomer. As I said, the normal fully-charged battery voltage is 12.8 volts. When the charging system is fully operational, the system voltage is closer to 14 volts. Voltage drops abound in every inch of wiring, and every connection and depend on temperature and current flow.

[ericread]

The alternator can produce more power as the RPM is increased.
As the output current increases the load on the battery decreases, thus the battery voltage goes up. Normal no-load battery voltage is 12.8 volts. Under load this can drop under 12 volts. The VR limits the charging voltage to about 14 volts. If you measure the battery voltage anywhere other than the battery posts the voltage will be less due to the resistance of the wiring between the measured points and the battery posts. The greater the current in the circuit, the greater the voltage drop.

If your voltage is going over 14 volts then the VR may be at fault.
If your voltage starts out at 12 volts and rises to 14 volts, then that is normal.
Measuring voltages in any system depends a lot on how the measurements are taken. It is never a trivial exercise. The idea of a 12 volt system in the 914 is really a misnomer. As I said, the normal fully-charged battery voltage is 12.8 volts. When the charging system is fully operational, the system voltage is closer to 14 volts. Voltage drops abound in every inch of wiring, and every connection and depend on temperature and current flow.

Please remember that there is a "bootstrap" process to these alternators. Whereas new alternators have permenant magnets and begin creating energy immediately upon start, our 914 alternators do not start creating any significant voltage until the unit is "bootstrapped" by reving the engine to between 1500rpm to 2000rpm. Once this has been achieved, the magnets are energized and the alternator should work normally. Until the bootstrap has ocurred, the voltage out will be significantly reduced.

This will never contribute to an over-voltage situation, but something to keep, in mind when working on the alternator.

When my car had serious overvoltage problems, I found the problem to be with the alternator itself. Once I replaced the alternator, all was (and is) well. Although the VR is supposed to limit voltage by providing feedback current to the alternator, if the alternator itself is foobar, then it's going to output any damn voltage it wants to. My old alternator was putting out about 17 volts, regardless of whether the VR was in-line or disconnected. Not good! (IMG:style_emoticons/default/headbang.gif)

The good part is that I can now change out an alternator in under an hour - by myself. (IMG:style_emoticons/default/aktion035.gif)

[ConeDodger]

You haven't said what the voltage increases to. If it is no higher than 14 the VR is working. If higher the VR may be the culprit but I have even had a recent situation where the battery was bad and would overcharge like crazy. Only thing that made sense was the VR so I replaced it with three used but known good ones and finally a new one. Still had the an overcharge. Optima Red Top by the way. Kind of a wave of bad Optima batteries lately... hmmm.

[drive-ability]

I would like to know the voltages, and what your using to measure the system. Whats the battery voltage with the key off?, running at idle and at 2500 rpm..

[highways]

Ok so let me take you guys from the beginning.

Week or two ago... alternator light came on, stayed on, at a normal brightness level. A swapped out the alternator with an unknown used alternator that 'felt' like it turned ok. Same symptoms with 2nd used unknown alternator.... alt light stayed consistently on. Meanwhile my voltage gauge on the console was showing 10 volts and steadily creeping downward if I drove for any period of time. Obviously- battery was not charging.

Picked up new VR from Performance Products. They sold me the wrong VR.... didn't fit and didn't look right. Didn't make the Alt light go off either.

Bought second VR from Pelican Parts. This one looked right, fit right, and had the correct part number. Plugged it in and started engine (on unknown 2nd alternator). Alt light went out... console voltage meter showed 12 volts at near idle. Thought I was good to go. Even got ambitious and threw my original alternator back in the car since i thought it spun smoother then the 2nd one. Car still started, Alt light goes off, 12 volts on the console meter. Looked good to go.

Then I go to drive around the block. Voltage increases to 14 with 2000-2500 RPM's. My headlights go drastically up and down when i step on the gas. there's also a new sound.... sounds like a high pitched turbine whistle which goes up in pitch with RPM's. Maybe the blower boot to the Alt was not seated tightly and whistling?? I was scared to drive over 2500 RPM's as I assumed that the voltage may increase indefinitely. I didn't know it may 'top out at 14 volts' and that may be OK.

Had battery checked at Sears. Guy said it was good, 10.5 volts and 650 amp hours. I had charged it an hour or two before he measured this. I don't totally trust that the battery is in the best shape though.

So I hope that explains things better. Should I drive a bit and see if it stays between 12-14 volts? If it goes above 14 volts does that mean i have a problem? I'm measuring voltage off my console gauge incase you missed that part.

PS. I'm going to take it around the block again and see if the voltage exceeds 14 volts at higher RPM's.

[orthobiz]

I only finished 1/2 of my Eveline Woods speed reading course.

And half of the Evelyn Woods spelling course!!!! lol

Paul

[highways]

Ok, so after a few revs.... upwards of 4500 RPM... voltage meter on console tops out at what looks like 14.5v (ofcourse it might not be an exact reading). But at least the needle doesn't peg out (gauge is calibrated up to 16v).

At idle, console meter drops to what looks like 11v. So headlights change in brightness alot still when I step on the gas. But the system does seem to stop at 14- maybe 14.5v.

Sounds like from what you guys are saying that it's working normal?

[ConeDodger]

Your charging system is fine now. Check and or change your grounds.

[highways]

(IMG:style_emoticons/default/beerchug.gif)

Thanks guys!