Voltage regulator problems still...

[DUK]

My '87 3.2l alternator is blowing the fuses in my car. It first happened last weekend at around 5500rpm under acceleration and so I thought it was the regulator or a ground. So today I changed the regulator and rechecked all the grounds only to still have the same problem. I'm getting voltage spikes up to 20 volts. This is detected by my megasquirt system (right up to the time it blows the 2amp fuse to it).

Any thoughts? Could the diodes be doing this? I ran this car for about 1500 miles with no problems (as far as the alternator goes). I did notice the voltage spikes every once in a while before but only to around 15.5 volts.

PS- it's a valeo.

[burgermeister]

I assume you've checked the battery connections and the few main ground straps (battery ground to chassis, tranny ground strap, that concoction of brown wires on the LH intake manifold on a 3.2)? If they're loose or intermittent, it will cause all sorts of havoc.
That's really my only idea ... I leave the rest to the experts.

[DUK]

Yea, ground problem is kinda what I was thinking but everything is new as far as wiring and checks out great with my ohm meter.

Any other ideas?

[Brian 162]

I had the same problem with my work vehicle. The alternator would charge 18.5 volts. The problem would come and go. Bottom line was they replaced the alternator and one battery.

[Walt Fricke]

Duke

I'd be puzzled too. Did you install a new regulator? I'm dubious that diode problems would cause overvoltage. But a bad regulator can. If the field current isn't regulated, the voltage is going to climb with RPM. I once installed a new regulator in our '84, only to have it go bad a couple of months later. Bad part.

In older cars with separate regulators you could have problems with the DF wire which carries the field current, but with the integrated systems it is hard to see that being an issue as long as the contacts are plugged in.

I am glad I have a voltmeter plugged into my cigarette lighter. Helped mid diagnose regulator death as it approached.

There must be a way to check the diodes with the alternator out, as you can get to their ends. But maybe putting an oscilloscope onto your electrical system might show if some unrectified AC is getting through?

Walt Fricke

[DUK]

Walt, Yes the regulator was new from porsche (actually a fellow pelican bought it and I bought it from him, but it was never installed)
I checked the diodes on the bench with my multimeter and they look great.

Had the alternator tested at two different well established rebuilders and everything tested perfect.

On their suggestion I've now ran a seperate 8ga ground directly from the battery to the alternator. But am still having the spikes.

Now I'm starting to wonder about my battery. It's a small gel cell like we use on the racecars (with little problems). I'm going to take it and load test it, it shows 12.56 volts on the bench and holds a charge great. Maybe it has a broken plate?

[Walt Fricke]

Duke

I have trouble seeing how a 12V battery (or 13.2, or whatever) could fail in such a way as to give off 20V. Easy to reduce voltages, harder to increase them.

The MSD, of course, is designed to increase voltage. I don't know what electronic devices there are on the Megasquirt (I've got a diagram somewhere, but not sure I'd understand it well enough to spot something capable of sending out voltage spikes). I'd suspect these two more than I would the battery. But easy enough to swap in a big heavy battery from somewhere.

The battery acts like a kind of damper, doesn't it? Like a big capacitor in a DC from AC voltage sourcer? Maybe the small battery doesn't fill that role? But there are lots of track cars out there with pretty small batteries (and even more with MSDs) who don't have this problem. And you aren't complaining that yours won't start the car.

Find a buddy with a portable oscilloscope so a passenger can watch what the voltage at the cigarette lighter is doing when things are acting up. Easy for me to say, though I'm not sure I know such a person, though I know some I'd ask were it my problem.

Walt

[RoninLB]

Wild Guess

I'd eyeball for worn slip rings or the brushes not molding the curve of the slip rings. If a finger nail catches I'd be suspect.

[DUK]

Ronin, The slip rings are worn probably .060" I was suspecting this myself, but the rebuilders that tested didn't seem concerned. I'm going to get a rebuilt alternator and try that next.

Walt, I totally agree with you, the battery surely can not produce extra voltage. I was thinking maybe a cracked or broken plate but I would think that would just cause a short.

[RoninLB]

Originally Posted by Duke Zink

Ronin, The slip rings are worn probably .060"

meaning the slip rings have .060" grooves ?

if so I'd try a rebuild.

[DUK]

Ronin- Yep they have about a .060" deep groove. New alternator on the way.