Voltage fluctuations

[MaximRecoil]

My car is a '69, but I converted to a solid-state electronic voltage regulator and a two-field alternator about 8 years ago. Recently the radio and gauges have been intermittently cutting out when the revs are high, such as when it goes to high idle after starting it when the engine's cold, or when going 55 or so MPH down the road. At first I thought it was due to bad connections so I cleaned all of the contacts in the bulkhead connector and in the fuse block, but that didn't help. Then it occurred to me that it might be an over-voltage issue, because the voltage regulator for my gauges is a modern solid-state electronic replacement which has over-voltage protection, so over-voltage would make them cut out.

I connected a battery tester to the battery while it was idling, and the needle was bouncing all over the place, and when I revved the engine, it bounced even more, with the peaks being off the scale (over 16 volts). I then replaced the regulator with a new one (BWD brand, part number: R296, from the Advance Auto Parts store - link). With that installed I got voltage at idle that was steadier than with the old one, but still constantly bouncing around between about 13 and 15 volts, and when revving, the voltage bounces around as wildly as with the old regulator.

Is the new regulator bad, or could the alternator be the problem?

[b5blue]

I'd make sure the ALT. housing is well grounded then check FLD. and main connections on the back of the ALT. first.

[John_Kunkel]

On the dual-field system, alternator grounding isn't critical but regulator grounding is. If in doubt, run a dedicated wire from the regulator to the battery negative terminal.

[MaximRecoil]

On the dual-field system, alternator grounding isn't critical but regulator grounding is. If in doubt, run a dedicated wire from the regulator to the battery negative terminal.

The regulator is perfectly grounded. I have a 10 gauge wire with ring terminals bolted to one of the mounting holes (bare, greased metal around the mounting hole) and the other end bolted to a threaded stud on the firewall (bare, greased metal around that too). I've also added a few short 4 gauge wires from various points on the body in the engine compartment to the engine block, and I have a 0 gauge wire going from the engine block to the negative terminal on the battery. I've checked grounds with a meter many times; perfect continuity (dead short) from anything that's supposed to be grounded, back to the negative terminal on the battery.

[Gold Rush]

I understand that you have checked and cleaned all the bulkhead connections but may suggest you go one step further and monitor the regulator reference voltage.  A few months ago I discovered my charging system was putting out 15.5 volts because the ignition switch was worn out and dropping almost two volts.  I'm not saying your switch is bad but it is worth checking to see if that reference voltage is correct.

I know how aggravating this sort of stuff is.  You'll solve it eventually..  Good Luck

[MaximRecoil]

I understand that you have checked and cleaned all the bulkhead connections but may suggest you go one step further and monitor the regulator reference voltage.  A few months ago I discovered my charging system was putting out 15.5 volts because the ignition switch was worn out and dropping almost two volts.  I'm not saying your switch is bad but it is worth checking to see if that reference voltage is correct.

I know how aggravating this sort of stuff is.  You'll solve it eventually..  Good Luck

Is the reference voltage measured at the field terminal that the green wire from the regulator connects to? Also, how high should the reference voltage be?

By the way, my ignition switch isn't causing any problems because it isn't in the ignition circuit anymore. All it does is trigger a relay in the engine compartment and then the current for the ignition system draws directly from a 10 gauge wire connected to the stud on the starter relay, which in turn is connected to the battery via an 8 gauge wire. That eliminated the ballast resistor as well. I did that several years ago when I converted to GM HEI electronic ignition.

Also, the alternator-to-battery charging circuit doesn't go through the bulkhead connector and ammeter anymore; the battery terminal on the alternator is connected to the stud on the starter relay with an 8 gauge wire and fusible link, which in turn is connected to the battery via another 8 gauge wire. I did that several years ago too.

[Gold Rush]

My experience is with my '74 but since you now have the electronic voltage regulator I expect it should function as mine does. 

If so, the run voltage from your relay should be applied to the voltage regulator contact that does not go from the regulator to the alternator field.  On the '74 the reference input comes in on a dark blue wire and the regulator output to the alternator field is a dark green wire. 

Hope that helps.

[Nacho-RT74]

On dual field system, blue wire is constant positive, green is regulated negative, being increased to feed the field accordingly with the voltage measurement.

[John_Kunkel]

Is the new regulator bad, or could the alternator be the problem?

Could be the alternator, especially if there's an internal short it would explain the wide voltage fluctuation.

[MaximRecoil]

My experience is with my '74 but since you now have the electronic voltage regulator I expect it should function as mine does. 

If so, the run voltage from your relay should be applied to the voltage regulator contact that does not go from the regulator to the alternator field.  On the '74 the reference input comes in on a dark blue wire and the regulator output to the alternator field is a dark green wire. 

Hope that helps.

I measured the voltage at the field terminal that's closest to the alternator's battery terminal, and it fluctuated between 13.5 and 14.2 volts. At the battery I used an old Snap-on battery/alternator tester which is analog (like this one), because it's easier to see voltage fluctuations on a needle than on a digital readout, and the needle was bouncing around from about 14.5 to 15.5 volts at idle, and bounced around even more when revving the engine. As a comparison, I used the same battery tester on 1980s Dodge pickup with a 318, which of course has the same type of alternator/regulator setup as my car does, and the needle held rock steady on that (I tested at the battery): about 14½ volts at high idle, and about 13½ at low idle.

Then I had my battery tested at the local auto parts store, and their gizmo said it has a dead cell. I don't see how that's possible though, because a 12 volt car battery has 6 cells, 2.1 volts each, connected in series for a total of 12.6 volts. If one cell is dead, the maximum possible voltage that the battery can hold is 10.5 volts. My battery (which is 2 years old) holds 12.6 volts fine, and cranks the engine like a brand new battery, even if I haven't started the car for a couple of months. I doubt a battery that's working on only 5 cells (10.5 volts) would even start a car at all, and if it did, it would be just barely. Also, I did a load test using that Snap-on battery tester; I held the load test button for 10 seconds and it stayed in the green, showing about 700 cranking amps (the battery is rated for 650 CCA).

Could be the alternator, especially if there's an internal short it would explain the wide voltage fluctuation.

Maybe I'll test it with a different alternator. I should probably test it with a different battery too. It's not possible for it to really have a dead cell like that gizmo claimed, but maybe there's some other issue with it that could be causing this?

[Gold Rush]

Sounds to me like the alternator terminal you checked would equate to the blue wire on my '74 which is not the regulator output (green wire).  Neither here or there.  Your problem really does not sound like a regulation problem. 

As John suggested I'd sure be suspicious of the alternator.  Like you, I'd be surprised to hear you found a bad battery.

[MaximRecoil]

Sounds to me like the alternator terminal you checked would equate to the blue wire on my '74 which is not the regulator output (green wire).  Neither here or there.  Your problem really does not sound like a regulation problem.

I made this diagram a long time ago showing how it's wired:



The terminal I checked the voltage on is the one at about the 10 o'clock position in that diagram, i.e., the one closest to the alternator's threaded stud which is at about the 11 o'clock position (output-to-battery terminal).

As John suggested I'd sure be suspicious of the alternator.  Like you, I'd be surprised to hear you found a bad battery.

I swapped in the battery from my truck and it did the exact same thing, so that probably eliminates the battery as the culprit. With the new regulator that I swapped in the other day, it still did the same thing as it did with the old regulator, so that probably eliminates the regulator as the culprit. I guess I'll order an alternator for it.

[Gold Rush]

Too bad you can't find a loaner alternator.  With all the swapping, checking, and replacing already done, the alternator seems the logical choice.   Hope it works out.

[metallicareload99]

I understand that you have checked and cleaned all the bulkhead connections but may suggest you go one step further and monitor the regulator reference voltage.  A few months ago I discovered my charging system was putting out 15.5 volts because the ignition switch was worn out and dropping almost two volts.  I'm not saying your switch is bad but it is worth checking to see if that reference voltage is correct.

I know how aggravating this sort of stuff is.  You'll solve it eventually..  Good Luck

  I've never considered that could be an issue, although it might not be his issue.  Maybe at least check voltage drop at the center terminal on the regulator tho

The terminal I checked the voltage on is the one at about the 10 o'clock position in that diagram, i.e., the one closest to the alternator's threaded stud which is at about the 11 o'clock position (output-to-battery terminal).
I swapped in the battery from my truck and it did the exact same thing, so that probably eliminates the battery as the culprit. With the new regulator that I swapped in the other day, it still did the same thing as it did with the old regulator, so that probably eliminates the regulator as the culprit. I guess I'll order an alternator for it.

What you've described is a lot like what happened the last time I had a regulator go bad.  That being said, it seems to be the alternator by process of elimination.  While the alternator case should be grounded, I don't think you should see any continuity what so ever between the output stud and ground.  Also if you have a decent voltmeter I would think you could check the diodes

[MaximRecoil]

The new alternator seems to have fixed the problem. When idling it's a steady 13.8 volts at the battery. Also, the engine idles much smoother when it's cold. Previously the engine ran at a low and rough idle when starting it cold, and after a minute or two it would ramp up to a high idle, and when I kicked it down to a low idle it would be relatively smooth, and stay smooth for as long as the engine was warm. Today when I started it cold after changing the alternator, it went through the same routine, except the idle was a lot smoother. I don't know if that had anything to do with the new alternator or if it was an anomaly.

[Gold Rush]

Glad to hear you got things working.  It doesn't surprise me that the engine ran a little rough with the alternator fluctuating like it was.  Changing load , especially at idle would have that effect.

What it our alternator output at 2500 rpm?

[MaximRecoil]

What it our alternator output at 2500 rpm?

I don't have a tachometer, but at higher idle the voltage at the battery was about 14.4 volts.

[Gold Rush]

YUP, I believe you cured the problem with the new alternator.   Those voltage readings are very close to my '74.

VERY GOOD !!!!

[Nacho-RT74]

I bet the problem was so easy to fix that didn't need to replace alt, just open it and spread away the diodes bank ends, from the rotor vent vanes  ( BTDT )

[MaximRecoil]

There's still a problem. After installing the new alternator, I didn't think to test the voltage under load, such as with the headlights on. It turns out that the voltage drops to about 11.9 volts with the headlights on at idle, though it comes up to about 14 volts when revving the engine. I took my car over to Advance Auto where I bought the alternator, and their gizmo said my battery was bad again, and wouldn't do any further tests on it. So I swapped in the battery from my truck, and this time a different guy did the test and with a different, more elaborate gizmo, and it said the battery and alternator were fine, and gave me a printout showing the results. So I showed him what it was doing with my multimeter, i.e., dropping to 11.9 volts at low idle with the headlights on. He had no explanation for the discrepancy between a plain-as-day voltage reading from a multimeter and his gizmo.

He said if I removed the alternator he could test it on a dedicated alternator testing machine, which I did, and it said the alternator was fine. Then I had him test my old alternator, and it said that one was fine too, with test results that were practically identical to the new alternator, which doesn't make sense, because the two alternators behave very differently in my car.

He allowed me to return the alternator, despite it testing good on his machine, and I reinstalled my old alternator, so I'm right back where I started.

[A383Wing]

chrysler alternators never charge at idle with lights on.....you can help that issue by putting the smallest pulley on the alternator so it spins faster

They make 3 sizes of pulleys....and I would have to check which the smallest size is.....I have the smallest on all my cars

you should have kept that new alternator

[MaximRecoil]

chrysler alternators never charge at idle with lights on

Defective by design? It's not a case of just not charging; it's draining the battery. 11.9 volts is 0.7 volts below normal battery voltage.

.....you can help that issue by putting the smallest pulley on the alternator so it spins faster

They make 3 sizes of pulleys....and I would have to check which the smallest size is.....I have the smallest on all my cars

you should have kept that new alternator

I'd rather have the battery not drain at idle with the lights on. The old alternator has ~12.7 volts at the battery at low idle with the headlights on, which isn't great, but it's still 0.1 volts above normal battery voltage (not charging significantly, but not draining either). The pulleys on both alternators looked to be the same size, though I didn't measure them.

How difficult is it to change the pulley, and where do you get different pulleys from?