Old car external voltage regulator woes

On my 72 Cutlass over there < I bought a Delco regulator about 4 years ago that required some tweaking to get a good charging voltage from. I got it set and haven’t looked back. It is the 2 coil type. The only issue I have is if I try to have a short stop on a trip. The engine compartment heats up and then the field will not contact and set up charging. It stays that way until I stop, cool off and then restart.

I know the Wells VR715 is the best bet but does anyone know why this happens? Is there a little adjustment I’m missing that could help keep this hot start from not charging my battery?

I would suspect the heat is causing a change in the resistance of the circuit that turns on the relay that regulates the charging voltage. You may have to lower the adjustment setting slightly in order to compensate for the change due to the heat.

I’ll look into that in the morning.

They make one wire replacement alternators with built-in regulators…

Gotta have the correct look though. Too many other things look the part.

Check that the field armature air gap meets the specification. Using the correct feeler gauge bend the upward limit tab until the feeler is stiff to pull out. You can probably tell by how much you have to bend the tab if you have solved the problem.

Hope this helps.

How much “tweaking” did you do? The Duralast VR-715 is likely a solid state unit with no adjustment. I would suggest that you remove the alternator and have it bench tested and replace it if needed, other wise replace the regulator with the solid state model and hope for the best.

I had to slightly adjust the regulator coil so the charging voltage was higher. Had the alternator checked before this started and did not have an issue with it.

@Reseacher, where do I find that spec to set it to?

The field relay pull-in voltage as I recall is not critical as long as it pulls in when either cold or hot and drops out on shutdown. You can reduce the armature air gap or bend the dropout spring tab, if present, to lower the pull-in voltage. I would try reducing the core-armature air gap first to retain the spring pressure to make sure that the armature drops out when power to the coil is removed at shutdown. If there is a slight bit of residual magnetism in the iron parts of the magnet structure, you want to make sure of dropout. The core-armature air gap may have a specification but it is not critical as long as the contact closes and opens as intended.

And if I remember right, if it does not open the battery discharges because the field is always on to the tune of about 1Amp?

Quote: "And if I remember right, if it does not open the battery discharges because the field is always on to the tune of about 1Amp? " Unquote

Correct, battery discharges but as I recall, the alternator rotary field current is around 3 amps. When setting the voltage regulation level, drive at least 10 minutes to give the system a chance to equalize with regard to voltage and temperature.

Correction added 9-11-12: The field current that I recalled was 3 amps was with the field at rest. Later when the alternator field (rotor) is turning and the battery is fully charged and there is minimal electrical use, the field current could very well taper down to 1 amp due to the field current being interrupted by the vibrating voltage regulator contact set.

The information I have is that the armature gap should be 0.015 inches and the point gap should be 0.030 inches. The pull in voltage should be between 6.3 and 8.3 volts. This is determined by putting a variable voltage source between terminal #2 and ground and raising the voltage until the relay pulls in. Alternately, you can use the cars 12 volts and a 50 ohm rheostat connected to terminal #2 and run the rheostat down until the relay closes and then read the pull in voltage at #2. You set the draw in voltage by bending “the heel magnetic leg”.

Another item of concern is the following. There is a 10 ohm 16.5 watt resistive shunt wire that is part of the wiring harness that shunts the charge warning light. The ignition switch supplies voltage to this wire and the charge warning light. These two paths provide the start up field current. Once the alternator is developing Alternating Current in the stator, the field relay is pulled closed and the field regulator is now connected directly to battery voltage shunting the resistive wire and the warning light. If the stator stops producing the appropriate voltage, the field relay will drop and the warning light will come ‘on’ if the ignition switch is in the ‘on’ position. Otherwise, the field circuit path is cut off. If the above resistive wire is open or has changed value, the warning light will not pass enough current to get the stator AC voltage up enough to close the field relay. The relay might close with the current draw from the warning light when the winding is cold and not when the winding is hot.

A quick check of the resistive wire is to turn the ignition ‘on’ engine ‘off’ and measure the voltage at terminal #4. If there is only minimal voltage discernible, the resistive wire is open. Also realize that the current from terminal #4 has to pass through the voltage regulation contacts, the brushes, and field winding so make sure that the contacts are clean and the rest of circuit is low resistance.

Hope this helps.

@researcher this is great information. Point gap = field relay, armature = regulation side relay? I checked the field relay gap last night and it was .060 inches. I arbitrarily changed it to 0.040 inch because I had not read this yet and 2/3 delta set point would at least get me some different response hopefully…
The wiring is new M&H wiring that supplies all the parts houses with their factory drop in harnesses. This does not say I have the right resistive element in the wire but I am not dealing with 40 something year old wiring either. All contacts in the circuit are clean. Additionally the mounting locations for the regulator are bare metal and there is a ground strap from the regulator housing to the back of the passenger head which also has paint removed for contact.

I didn’t take the car for a ride last night. I just put everything back as it was with the change to the gap. It sounds like I may still be too far open from this information but would be an easy test to see if anything has changed in performance. I will check the voltage on pin 4 before I ride around.
Thanks for this information.

The armature gap referred to is the separation between the armature pole of the field relay winding and the magnetic piece that is pulled down on the same relay. The book I referenced did not specify the procedure for setting that gap. I assumed that a inspection might puzzle out the piece to bend.

I suspect that closing the field point gap to 0.030 would bring the armature gap into specification. I suspect you found the problem by resetting to 0.040.

BTW, in your inspection of the relay, could you see what they are talking about when they say 'bend the magnetic heel". The picture showed a tool on a metal piece opposite to the points.

Regarding the wiring harness, the resistive element might be a postassembly installation piece. It would most likely be specific to each RPO alternator available on that model. BTW it is connected with crimp connectors i.e. no soldering allowed.

Thank you for the feedback.

I have read that somewhere about the heel gets bent but I found the static side of the points arm was easy enough to move and that is what I moved. As for the resistive wire, I’m just not sure where it would be as an add on wire. The harness was complete in all connections and I don’t remember any detail about it in the chassis assembly manual when I was putting the car back together.

I have some things to do this weekend that should allow for driving this old car around. I did a lot of work on another external regulator car and that one would arbitrarily stick the field when you least expected it to, then dead battery when you came back to it. Thanks again for this information.

I finally started the car last night. Field appears to not pull-in until higher RPMs now and will not hold under idle. I didn’t come back to Reseacher’s comment here but did pull down some old Chilton manuals from the closet and found the spec of 0.030" point gap and 0.015" air gap. This measurement only makes sense if the air gap is measured when the points touch closed since it would not allow enough travel, i think, if I make the air gap 0.015" when the points are open. I think that would hold the points open for ever.
The spec also talks about close voltage that Reseacher stated above so I will check that today on the bench to ensure it is closing properly. Bending the point side was not the correct method since it left the air/armature gap too large I believe. I will know more this afternoon when I get some time with a bench supply. To adjust the gaps just bending the tab behind the coil is the better movement and is very easy to control that movement.

Funny thing Chilton manual for 72-79 says no Olds used external regulator but has a better section in the troubleshooting for it. The manual for 6x-71 shows the specifications for the actual gaps. That is bad to need 2 books for one problem.

Something is screwy there. Once the points are closed, the field supply voltage should go to B+ i.e. shunting out the indicator light and turning it ‘off’. With the field relay closed it should stay latched until the stator AC drops below the relay hold in voltage. Maybe the field relay contacts have a voltage drop across them or the regulator points are ohmic. Something is limiting the field from getting the required current to hold the stator voltage up.

I tested it before I left work today. I had to bend the heel a little more and back out the changes I made to the point foot. I ahd it closing (snapping) shut at 6.4V and releasing somewhere around 3.5V. I also looked at the regulator side and found it was measuring high with a true DC source. I should have left this one alone. I put it back on the car tonight and had to immediately bend the lower spring perch lower (providing more tension) to get the charging voltage a little higher. I went for a ride. I think it is charging better now but the cig lighter volt meter was loosing contact while driving. I disconnected the power from the cig socket and cleaned it with sand paper. I will see tomorrow night if it is a little better contact. If not, I’m throwing a digital VM on it for my next ride to a fuse tab.

Ya know I lived on these cars and you guys are confusing the hell out of me. Get a dwell meter and a timing light, replace the condenser and points, set appropriately.

@Barkydog-- You are thinking about the distributor on the old cars that had a condenser and points. In the bygone days, cars had electro-mechanical voltage regulators. These had electromagnets (two for an alternator set-up and three for a generator set-up). These electromagnets opened and closed contact points to control the voltage and the amperage from the generator or alternator.
I am surprised that a 1972 Oldsmobile used this type of regulator. My 1965 Rambler had a solid state regulator that was external to the alternator. As best I can remember, the regulator was manufactured by Motorola.