1968 Battery Drain / Voltage Regulator Problems.

[Paul P.]

My very late build 1968 four speed convertible developed an electrical gremlin that I've been working on and off since November.

Current draw, everything off, is 3.2 Amps measured at the battery. It can be intermittent.

After lots of troubleshooting (pulling all fuses, etc.) I've narrowed it down to the voltage regulator. I know that as when I disconnect the two wires at the alternator that go to the regulator, the current draw goes down to zero. Also, when the voltage regulator is removed there is zero current.

I've tried three different voltage regulators in addition to the one that was on the car. Same thing - 3.2 Amps current draw when connected, none when the two wires going to the alternator are disconnected. Two of the voltage regulators were soured from a reputable Corvette supplier, the other was a Wells VR-715 solid state voltageregulator from my local auto parts store. FWIW, the car charges fine as indicated by the ammeter and a nice 13.8 volts at the battery.

The alternator was rebuilt by a local rebuilder. I guess it is possible for the rebuilder to have missed something and the problem is with the alternator.

Now thinking about my options. One is to replace the alternator / voltage regulator with a 1969 alternator which (I'm told) has an internal voltage regulator. My '68 is a nice driver with non-original motor, so losing face at a concours judging is not an issue for me. Would the fitment be the same?

I have a background as an electronics technician and a good digital multimeter.

Any comments?

[Joe L.]

Re: 1968 Battery Drain / Voltage Regulator Problems.

My very late build 1968 four speed convertible developed an electrical gremlin that I've been working on and off since November.

Current draw, everything off, is 3.2 Amps measured at the battery. It can be intermittent.

After lots of troubleshooting (pulling all fuses, etc.) I've narrowed it down to the voltage regulator. I know that as when I disconnect the two wires at the alternator that go to the regulator, the current draw goes down to zero. Also, when the voltage regulator is removed there is zero current.

I've tried three different voltage regulators in addition to the one that was on the car. Same thing - 3.2 Amps current draw when connected, none when the two wires going to the alternator are disconnected. Two of the voltage regulators were soured from a reputable Corvette supplier, the other was a Wells VR-715 solid state voltageregulator from my local auto parts store. FWIW, the car charges fine as indicated by the ammeter and a nice 13.8 volts at the battery.

The alternator was rebuilt by a local rebuilder. I guess it is possible for the rebuilder to have missed something and the problem is with the alternator.

Now thinking about my options. One is to replace the alternator / voltage regulator with a 1969 alternator which (I'm told) has an internal voltage regulator. My '68 is a nice driver with non-original motor, so losing face at a concours judging is not an issue for me. Would the fitment be the same?

I have a background as an electronics technician and a good digital multimeter.

Any comments?

Paul------


I don't think you can just install the internal regulator alternator and you're done. I believe that wiring changes would also be necessary.

Beyond that, I don't think that just going with an internal regulator alternator is going to solve your problems. If you think there might be a problem with your rebuilt alternator, then what I might try would be to buy a commercially rebuilt alternator (they're quite inexpensive), install it and see what happens. If it works and you want to keep a correct numbered case, just take the guts from the commercially rebuilt alternator and transfer it to your case. Otherwise, just use it as-is. However, I actually don't think this is going to solve the problem you have.

The other improvement I think I'd make is to have your electro-mechanical voltage regulator converted to solid state.

[Richard G.]

Re: 1968 Battery Drain / Voltage Regulator Problems.

Does the draw drop to zero after you pull the plug on the alternator?

[Paul P.]

Re: 1968 Battery Drain / Voltage Regulator Problems.

Richard:
By "the plug" I assume you mean the two smaller gauge green and white wires that connect to the voltage regulator? Yes, the current goes to zero. (FWIW, my '68 is missing the plastic housing, I just have two female connectors)

Or are you referring to the single heavy gauge wire that connects to the bolt? I know if I remove both, the current goes to zero. I haven't tried just disconnecting the single heavy gauge wire and leaving the two smaller wires intact. I'll have to try that tomorrow when I get a chance.

Joe: I wouldn't think that there would be wiring changes in installing an alternator with integral voltage regulator but then I have no direct experience.

I thought about having the voltage regulator converted to solid state, but the VR-715 is a solid state unit. You can sort of tell as it's significantly lighter than the original. My assumption is that those that do the conversion basically install the same innards found in the VR-715 but I don't have direct knowledge of that.

~Paul

[Richard G.]

Re: 1968 Battery Drain / Voltage Regulator Problems.

Yes this it what I meant; the two smaller gauge green and white wires.

When the key is turned on the system supplies power to the alternator field windings. So the issue isn't likely the regulator as you have the same issue with multiple regulators. I suspect some how the ignition on wire is always hot for some reason? I would trace the wiring out and see if the ignionon is sending power to the regulator with the key off. If this is so, the regulator is doing what it is designed to do, turn on the windings when the key is on. Possible the feed wire is hot all the time? You might try unplugging the ignition switch plug and see if the amps drops to zero.

[Dan D.]

Re: 1968 Battery Drain / Voltage Regulator Problems.

Paul, I think your problem is leaky diodes in the alternator. You say your alternator was rebuilt, and if you remove the wires the current goes to zero. These are all the indications of a bad alternator. Try a new one. I think that will solve your problem.

-Dan-

[Edward B.]

Re: 1968 Battery Drain / Voltage Regulator Problems.

Common complaint. Bad alternator diode.

[Richard G.]

Re: 1968 Battery Drain / Voltage Regulator Problems.

I am missing something.
With "all off" I am assuming the ignition is in the off position and the drain is what is typically described as "overnight" style battery drain. Under these conditions the regulator shouldn't be providing any voltage to the alternator. With the vehicle off the only wire attached to the alternator that is hot is the large diameter red wire attached to the output stud... How would a defective or leaking diode cause a load under this key off condition? I am not saying this isn't the case, just I don't understand how it would work.

Alternator.GIF

Normally, if the engine is not running, the diodes are reverse biased and do not conduct current. If one of the high side diodes is shorted then the diode trio (another set of three diodes supplying the regulator/rotor) could conduct and drain the battery. The current source would be through the large red output wire not the field winding plug.
Thanks
Rick

[Dan D.]

Re: 1968 Battery Drain / Voltage Regulator Problems.

You are correct Rick, the drain is through the red (output) wire. But if one or more diodes is leaking, it will feed voltage to the neutral termination of the 3 phase delta configured stator windings. This in turn will supply power through the 'S' (neutral) terminal of the 2-wire plug back to the regulator and pull in the field relay in the alternator. The relay coil provides a current path to ground. You have to see a schematic diagram of the alternator/regulator circuity to understand it completely.

If Paul replaces the alternator I think his problem will go away.

-Dan-

[Richard G.]

Re: 1968 Battery Drain / Voltage Regulator Problems.

Dan, I appreciated the explanation.
Hopefully, Paul has the original alternator and can just have the diode replaced and be on the road again!

[Joe L.]

Re: 1968 Battery Drain / Voltage Regulator Problems.

Richard:
By "the plug" I assume you mean the two smaller gauge green and white wires that connect to the voltage regulator? Yes, the current goes to zero. (FWIW, my '68 is missing the plastic housing, I just have two female connectors)

Or are you referring to the single heavy gauge wire that connects to the bolt? I know if I remove both, the current goes to zero. I haven't tried just disconnecting the single heavy gauge wire and leaving the two smaller wires intact. I'll have to try that tomorrow when I get a chance.

Joe: I wouldn't think that there would be wiring changes in installing an alternator with integral voltage regulator but then I have no direct experience.

I thought about having the voltage regulator converted to solid state, but the VR-715 is a solid state unit. You can sort of tell as it's significantly lighter than the original. My assumption is that those that do the conversion basically install the same innards found in the VR-715 but I don't have direct knowledge of that.

~Paul

Paul------

At a minimum, the plugs are different between external and internal regulator alternators. If you are using a VR-715 regulator that is solid state. So, you are all set with respect to that. I only recommend the conversion if one wants to have a regulator with the outward appearance of original.

I agree with the others and still advise changing the alternator to a commercially rebuilt unit. Even a high quality AC Delco rebuild will only cost you about 40 bucks. I think that if your alternator is defective (as I highly suspect it is), whoever rebuilt it for you failed to test the components before rebuilding it. That's really inexcusable as they are very easy to test.

[Paul P.]

Re: 1968 Battery Drain / Voltage Regulator Problems.

All good suggestions, thank you Joe, Paul, Richard, Edward and Dan.

I had not thought about checking the white and green wires for voltage with everything off. I would think the there should be zero volts there? I know there will be 12 volts at the large main wire as that is essentially a direct connection to the battery.

I'm now getting suspicious of the ignition switch. Maybe it is connecting even though the key is out and it's in the vertical position? That might explain the current drain and it's intermittent nature. FWIW, the car does have a Pertronix, I don't know how they react to the ignition being inadvertently turned on all the time. It works OK (the car starts up as expected) not sure what the current drain is under those circumstances.

I actually do have another rebuilt alternator that I will try. I installed it but the cooling blades were stuck against the long adjusting bar (not sure of the correct terminology) preventing it from turning. The original had cooling blades that are a smaller diameter. There is a large bolt securing it and I doubt I have the wrench to handle it. I'll do some research into taking it off as well as other alternator disassembling procedures and see where that takes me.

Thank you again for the help.

No Surrender,


Paul

Paul------

At a minimum, the plugs are different between external and inter thought about nal regulator alternators. If you are using a VR-715 regulator that is solid state. So, you are all set with respect to that. I only recommend the conversion if one wants to have a regulator with the outward appearance of original.

I agree with the others and still advise changing the alternator to a commercially rebuilt unit. Even a high quality AC Delco rebuild will only cost you about 40 bucks. I think that if your alternator is defective (as I highly suspect it is), whoever rebuilt it for you failed to test the components before rebuilding it. That's really inexcusable as they are very easy to test.

[Paul P.]

Re: 1968 Battery Drain / Voltage Regulator Problems.

So I did replace the alternator with a commercially rebuilt unit and all seems to be working now. It's been over a month with no current drain; the car starts regularly as we would expect it to.

The alternator fitment problems turned out to be an issue with the upper alternator bracket. My '68 has a non-original motor and the bracket was - from what I could tell - an aftermarket replacement unit commonly available in auto parts stores. I went to my favorite Corvette boneyard and purchased an original bracket which worked out great.

I'm thinking about rebuilding the original alternator with the intermittent current leak but I am kind of hesitant. My concern is that whatever caused the current leak might still be there after the rebuild.

Thanks to all for your advice, it is appreciated.

~Paul

[Joe L.]

Re: 1968 Battery Drain / Voltage Regulator Problems.

So I did replace the alternator with a commercially rebuilt unit and all seems to be working now. It's been over a month with no current drain; the car starts regularly as we would expect it to.

The alternator fitment problems turned out to be an issue with the upper alternator bracket. My '68 has a non-original motor and the bracket was - from what I could tell - an aftermarket replacement unit commonly available in auto parts stores. I went to my favorite Corvette boneyard and purchased an original bracket which worked out great.

I'm thinking about rebuilding the original alternator with the intermittent current leak but I am kind of hesitant. My concern is that whatever caused the current leak might still be there after the rebuild.

Thanks to all for your advice, it is appreciated.

~Paul

Paul------

Your concern is legitimate. However, what you could do is to gut the original alternator and replace all the internal parts with new. These are available in the aftermarket or NOS. Them, you'd have a brand new alternator with an original case. You could also buy another rebuilt alternator and transfer its internal parts to your case. I guarantee that no problems will "creep over" from the original alternator if you do either of these.