Bad Voltage Regulator???

[dunnm]

Hey guys, my battery has been overcharging recently and I'm trying to figure out why. I adjusted the Motorola VR to put out about 13.8 volts at 2000RPM (as I read here is correct) but when I increase RPM's I get an extra volt per 1000 RPM's (so I'm getting almost 18 volts at 5000 RPM!!). I'm guessing this would explain the light in dash is on steady at idle and gets slightly dimmer as I increase RPM (the voltage on either side of the light is not equal?). I read that the VR acts as a switch so am I to assume that it should "switch OFF" if voltage reaches a certain level?? So my question is, is it simply a bad VR or should I be troubleshooting elsewhere? If so should I stick with Motorola or is there a better option?

Thanks in advance.

Matt

'71 911T

[rick-l]

Where is your voltmeter connected when you read 18 volts?

[dunnm]

at the battery

[rick-l]

On the actual battery terminals or the clamps that go to the battery.

Ooops. I just read the body of the first message and didn't catch the vintage of the car. This is an electro-mechanical voltage regulator right?

[dunnm]

With car off battery reads just over 13.3 at the terminals.

[DRACO A5OG]

18??? oh no way too much.

Remove alternator and have it tested at 2 different places to insure it is the VR. bring the fan belt half and nut, shops will not have it.

[Targalid]

I am no electronic expert but I can tell you what I did when I had a similar problem. I experienced either no alternator output or voltage spikes. I monitored the voltage with a cigarette lighter mounted voltage meter. I could see transient voltage in the 17 volt range. When I inspected the original Marchal electro-mechanical voltage regulator, it was clean inside with all the contacts looking shiny and new. Nevertheless, I replaced this 36 year old unit with a new Huco solid state voltage regulator and my voltage spikes were eliminated. My low alternator output was traced to a loose connection at the 14 pin engine connector and the blue wire (pin 11 on my connector) which provides excitor voltage to the alternator. I guess if I were you I would verify clean connectors on the excitor circuit first (blue wire that energizes the excitor and the alternator bulb in the instrument cluster) though it may be that your ancient voltage regulator has failed.

[wwest]

"I adjusted the VR...."

Buy a new VR, solid state VR.

How did you go about adjusting the VR's voltage regulating relay's armature spring tension?

That can be done but not something I would attempt.

VR operates in a PWM mode, relay opens and closes at a high rate with dutycycle inaccordance with battery state of charge plus electrical loads.


Sound as if the relay contacts are stuck/sticking closed.

[dunnm]

As per a previous post I had read here, I released tension on the spring ( by bending metal tab) to decrease voltage output. This worked and I was able to get about 13.8 at 2000 RPM, but RPM increases increased voltage.

[wwest]

Originally Posted by dunnm

As per a previous post I had read here, I released tension on the spring ( by bending metal tab) to decrease voltage output. This worked and I was able to get about 13.8 at 2000 RPM, but RPM increases increased voltage.

I suspect that might only work with an adjustable bench power supply.

State of battery charge would be a real wild card using battery post voltage measurement to adjust the spring.

Haven't done any of this as of recent but be sure and finely burnish the relay contacts before adjusting.

Alternator voltage output rises with the relay contacts closed, relay should open as soon as the rising voltage reaches the float voltage level, rotor field then begins to collapse.