too much voltage

[lastcuda]

What should the voltage be at the output terminal of a 3 wire alternator with the wire disconnected. Intermittantly I'm getting almost 24 volts at about 1200 rpm. Hooked back up, i was getting up to 17 volts at 1100 rpm at the battery and shut it off. Headlights and dash lights get real bright and amp gauge pegs out on charge side. It has come and gone a couple of times recently. I'm thinking the alternator must be bad and the regulator is trying to bring voltage down but it's too much. All connections and grounds look good. Anybody got any answers for this? Thanks

 

[Mopars & Missiles]

The fact that you state its "intermittent" leads me to believe the regulator is the probable culprit, not the alternator. Regulator must have a solid battery ground reference to operate correctly. Also, any voltage drops between battery POSITIVE and the regulator "Ignition" input will cause alternator output to increase. Voltage drops can occur at any connector, the ignition switch itself, or any point in the electrical system that has some corrosion present which prevents a good solid connection.

If you had a shorted or open diode in the alternator, it would be a "constant" problem, not an "intermittent" one.

 

[lastcuda]

The fact that you state its "intermittent" leads me to believe the regulator is the probable culprit, not the alternator. Regulator must have a solid battery ground reference to operate correctly. Also, any voltage drops between battery POSITIVE and the regulator "Ignition" input will cause alternator output to increase. Voltage drops can occur at any connector, the ignition switch itself, or any point in the electrical system that has some corrosion present which prevents a good solid connection.

If you had a shorted or open diode in the alternator, it would be a "constant" problem, not an "intermittent" one.

Thanks for the advice. The battery ground reference is the connection from the case of the regulator to the firewall/engine ground strap, correct? Any good way to tell for sure if it's the regulator or a connection-caused voltage drop? I'll look at wiring diagrams when I get home and try to narrow down what connections to start checking too. I'd hate to replace regulator only to find out the problem is somewhere else. Again, thanks for your help.

 

[mmissile]

Had a similar issue. Bad and corroded wiring contacts/grounds. It took a couple days to find them all.

 

[Mopars & Missiles]

Yes, the ground reference is through the metal case of the regulator to the chassis ground. Good way to check it is with a DVM, check continuity from the VR metal case back to the negative post of the battery. Should be as close to ZERO ohms as possible. If you can zero out the leads of the DVM prior to making the measurement, it will be even more accurate. Alternate method is to use the VOLTAGE scale of the DVM, same connection points only you are reading millivolts instead of ohms. Again, as close to zero as possible is best. If you see much in the way of Ohms or millivolts (depending on which test method you use) then your VR ground reference is not really at ground.

For the ignition voltage input reference, use your DVM to accurately measure the battery voltage across the battery posts. Then measure the voltage at the VR ignition input terminal and the battery negative post. Compare the two measurements, if much of a difference between them you probably have some corrosion at a wiring connection somewhere between the battery positive and the VR. If there is much of a voltage drop, this will cause the VR to increase the alternator output voltage like you have been seeing. And since it is intermittent, it is most likely a wiring connection or the ignition switch itself. Only methodical step by step troubleshooting will find it. Throwing parts at it only wastes money and seldom corrects the actual problem. Good luck!

 

[lastcuda]

Again, thanks. That helps a lot. I'll let you know what I find. I knew there would be someone on here that has seen this before.

 

[704406]

I had a similar problem with high voltage output at alternator, it was the firewall bulkhead connection had partially melted the positive feed from the alternator to the dash amp gauge. As all voltage from the alternator goes thru the bulkhead connector 45 year old wiring can give trouble. Good luck!

 

[lastcuda]

I looked at the engine side of those connection plugs because I have seen that problem discussed here before. Everything looked good and I had replaced the engine harness several years ago so all that is fairly new. I have not checked under the dash though. I don't have A/C or any other accessories so I didn't think I would have an overheating problem there like I've read about. It seems a little confusing to me in that the current through the gauge would just be charging current and not current draw from accessories. I must be missing something there. Anyway, I'm not driving it until I figure this out. Thanks to all you guys.

 

[704406]

I looked at the engine side of those connection plugs because I have seen that problem discussed here before. Everything looked good and I had replaced the engine harness several years ago so all that is fairly new. I have not checked under the dash though. I don't have A/C or any other accessories so I didn't think I would have an overheating problem there like I've read about. It seems a little confusing to me in that the current through the gauge would just be charging current and not current draw from accessories. I must be missing something there. Anyway, I'm not driving it

 

[704406]

My engine side was fine as well, it was the dash side that was melted. The wires just melt because of bad or corroded terminals. As ALL voltage and current go thru the bulkhead connector to the dash gauge, if everything else is good defiantly check the connector and the wiring at least 6 inches from the terminal

 

[lastcuda]

Finally had some time to do some checking and of course it was working right after I checked ground and for voltage drop to VR. I was at 12v at the battery and 11.7 at the bulkhead disconnect, the plug on the steering column going to ignition switch and the input terminal to the VR. The back side of the disconnect showed no sign of anything heating up. I started it after I didn't find anything and it was putting out 12.7 to 13 as I revved it up to about 2000 rpm or more. I guess I'll just have to keep checking until I catch it doing something fishy (no pun intended). Again, thanks for everybody's input. It helped a lot to know where to start.