The Stovebolt Site Forums The Shop Area The Electrical Bay Pulsing Amp Meter (& Lights!)

I recently did lots of work under the hood of my '55 2nd. It has a late 60's 350ci, all 12VDC system. Before this work, I didn’t have this problem. Electrically, I did a lot, including: new 3-wire alternator (built-in voltage reg); new electronic ignition (coil, dist, plugs, wires); new fuse panel; elec radiator fan; and electric windshield wipers. I removed the old point ignition resister, and removed the old point type regulator from the circuit (it's still on the firewall, but no wires). My old original Amp gauge would swing wildly between charge & discharge. I worried about it, so I bypassed it. Now the only negative symptom is my dash and headlights flash bright/dim as the RPMs rev up as I drive. When I come to a stop and idle, they appear normal. A friend thinks my voltage regulator is half-wave rectifying (i.e. passing AC current). The truck runs great, the battery charges, etc. So what’s up with the pulsing amp meter and lights? :confused:

I'm inclined to think that there's a bad diode in the alternator. The diodes are what converts the A/C current to D/C current, what you are seeing is the wave pattern going from positive to negative. This needs to be addressed before running the engine again, as it can damage electronic parts and will kill your battery. I'd suggest changing the alternator, if it was a new/re-man part, look into warranteeing it out, as it is defective.

Fla'da Boy,

I have heard a bad diode in a alternator will sometimes cause it to whine, and will provide a drain for the battery.

The internal regulator, unless being "told" to vary the output, would be my first thought

Regardless, this would be considered 'the alternator' so I would think LONGBOX has the right idea about a swap or warranty return.

I would make sure my #2 wire was tied into the system properly and fit tight at the DA plug.

The only other thought would be a loose or broken plate in the battery.

I hope your auto supply house will take a return on a electrical item.

Stuart

Thanks for reply. I'll pull the alternator and take it for a test. It'll be interesting to see if their analog volt meter pulses at high RPMs. My digital shows the voltage varying slowly between 14 & 16 VDC. It only shows 1 to 2 VAC.

Which is the # 2 wire, the blue or the white off the DA plug? And where exactly should it go from there?

Fla'da Boy,

I am not sure colors are universal. The #2 spade on the alternator should be marked as such. Previous posts indicate it is the larger of the two wires, and more commonly red...

This wire senses system voltage and reports back to the alternator regulator to 'go or whoa'.

It CAN be looped around and connected to the power lug of the alternator. Some folks like it elsewhere.

Dirty slip rings or worn brushes could be causing your problem too...I think!

[edit] It shouldn't get to 16 volts..
Stuart

OK. I took the alternator to Autozone and had it bench tested. Their analog volt meter read a steady 15.5 VDC, toward the high side of the green "OK" zone, which looked to be about 14-16 VDC.

I found that Alt # 2 is the blue wire, and it is jumpered to the BATT terminal on the Alternator. Alt # 1 (white wire) goes to the Alt.Excitor terminal of my new Painless fuse block.

atomarc, I'm with you, I think 16 VDC is too high and will damage my battery and maybe other things. I suppose it is possible that the voltage regulator begins to maalfunction when it gets hot.

I don't know what to try next.

Could your battery cables not be tight or not a good enough ground from the battery to the engine and frame? The fluxuations would indicate an open somewhere between the alternator and the battery.

ALL of the wiring under the hood is brand new, and very well done. The guy that did the work is a master electrician with Obsessive Compulsive Disorder. There are no splices, every end has a professionally crimped & heat shrink-wrapped connector. It could be WRONG wiring, but it's not BAD wiring, if you see my meaning.

I checked the neg. battery post to the alternator body and truck frame, 0.2 ohms. I checked the pos. battery post to Alt Batt terminal, 0.2 ohms. Of course, this is all with the engine off, and cool.

What do think about putting my old external voltage regulator back in a series circuit along with the internal regulator?
Does anyone see a problem with double regulators?

Fla'da Boy,

I thought 14.8 was just about max on these alternators.

The Autozone test might not be comprehensive enough to declare your alternator "guilt free" as the source of your problem.

The easy test would be to swap units with a friend and see what happens.

Stuart

Do not try serial regulators.

Does the voltage fluxuate at the battery the same as it does at the dash?

I don't think I would use both regulators. As baldy said have you checked you out put at the battery?
Come to think of it I had a bad amp meter one time that was causing my headlamps and other items to surge. I don't know why but when I replace the meter it all worked fine.

Hey I spoke with another old guy tech. on this problem. He said in addition to what has been posted that he had an alt. that had bad brush spring in it and it caused the same problems.
It made the brush jump up and down and caused radical swings in the amp guage and the headlamps would dim and brighten.
Old guy technitions (excuse me, MECHANICS) are invaluable. If is really weird they have probably seen it.
The differance between a tech. and a mechanic is; the mechanic can listen to it and tell you what is broken, the tech. has to hook it to a machine first.

Good post, Toyvo. I spoke with a guy late Friday who has been working around cars for years, and he mentioned the same thing. I think I'm going to buy a new (rebuilt) alternator and see what heppans. I thought about a rebuilt kit and doing it myself, but a rebuilt alternator is only a couple $ more. I'll let you know.
Thanks,
Dave

cool dave, let me know.

It was the alternator all the time. I should have known, it was "free". The neighbor of the guy who did the work had a "perfectly good" alternator in his garage from when he upgraded the alt in his '74 El Camino. It was free; I used it. Nobody's fault but mine.

I'll never know if it was the brushes, or the regulator. But the problem was intermittent, because just before I changed, the Amp meter was rock solid for about 15 minutes. I revved the RPMs up a couple of times, and the Amp meter started hopping again. The regulator is solid state, so I think it was the brushes like Stu said.

Thanks to everyone for all the help. I need to put some pictures on the site so you can see MY Stovebolt.

Dave

The brushes could have contributed to what you just described as intermittent, but would probably have given you a lower than normal voltage. The current that flows through the rotor windings creates the magnetic field, that causes the current flow in the stator windings. Bad brushes, no current in the rotor, no magnetic field, no generator output.
The high voltage is more likely a regulator problem.

Richard --- Not the brushes them selves but rather the brush spring. Brush bouncing on rotor connection.

I apologize. When I wrote, "The regulator is solid state, so I think it was the brushes like Stu said.", I meant to say,"... like Toyvo said."

It is possible that with the brush hopping on the armature, that the regulator was attempting to compensate for the fluctuations in output, and thus proportionately clamped and passed the output as the brush hopped.
In control theory, this would be called a harmonic output, where the DC regulator is simulating an AC waveform, or wild hysteresis around the set point (14.4 VDC). When the brush lifts off the armature, the regulator reacts instantly to the drop in voltage, and slams open the output, giving a momentary reading of 16.5 VDC as the brush makes contact aagain.

We’ll never know for sure, I turned in the old alt as a core. Good riddance.

Thanks again, Dave

Cool beans Dave. Now drive he[l out of her before she lays down again.