1.5v drop in alternator field circuit, but .5 w/o VR?

[BillGrissom]

15.5v across the battery posts due to a 1.5v drop at the alternator field plug (blue wire). ... I have increasingly large voltage drops as I move farther along the harness out towards the alternator and despite my best efforts (over a freaking year and a half time span), NOTHING has changed.

I am jumping back in after a long time, so forgive me if I missed something. You sound hung up on the voltage drop to the alternator field supply wire. Don't worry about that. What matters is the IGN1 voltage at Vreg. You might need to pierce the wire insulation to measure (there are sharp multimeter probes for that). Measure IGN1 relative to the case of Vreg (what it controls).

That drop should be ~14 V w/ engine running. If too low, Vreg commands "more alternator" by lowering the 2nd field connection (flows back to ground thru it). If too high, it commands "less alternator" (2nd field voltage increases). If doing that, Vreg is doing its job. If the battery is running higher, find the voltage drop(s) on either the supply or return side. You might have a 1.5 V drop from the Vreg case to BATT-, especially if relying on a rusty sheet-metal screw for that path (or a corroded frame to BATT- jumper). I ran a ground jumper to my Vreg, coated w/ silicone grease, and I am using the same later Vreg in my 1965 (triangle connector). I also have two direct BATT- to frame wires since I used battery wires from a Jeep GC, and designers learned to ground cars many places (some of our issues).

 

[DionR]

You sound too hung up on the voltage drop to the alternator field supply wire. Don't worry about that. What matters is the IGN1 voltage at Vreg. You might need to pierce the wire insulation to measure (there are sharp multimeter probes for that).

The next stop in the wire is the VR and it's about a foot away from where I am testing, so the drop at the VR will at best be 1.5v. I'm hung up on it because at that point it should be much lower and it is driving the alternator output up.

And I don't just have a high voltage drop at the alternator, I have it through out the system, from the amp gauge to the alternator, with each location I check having a great drop than the last as I move towards the alternator. I've referenced the drop at the alternator today just because I don't want to have to repeat all of the numbers that I posted a year ago, both because it is time consuming and because they haven't changed.

If too low, Vreg commands "more alternator" by lowering the 2nd field connection (flows back to ground thru it). If too high, it commands "less alternator" (2nd field voltage increases). If doing that, Vreg is doing its job. If the battery is running higher, find the voltage drop on either the supply or return side.

As I understand it, the VR is the ground path for the alternator and all it does is open or close the ground. Voltage too low - ground is closed and alternator outputs. Voltage too high - ground is opened and alternator output stops. The rapid fluctuation of opening and closing the ground is what maintains the 14v or so. That's why the old style VR's vibrated.

You might have a 1.5 V drop from the Vreg case to BATT-, especially if relying on a rusty sheet-metal screw for that path (or a corroded frame to BATT- jumper). I put a ground jumper on mine, coated w/ silicone grease, and I am using the later Vreg in my 1965 (triangle connector).

I've cleaned and checked the ground on the VR, all is good there.

 

[67Dart273]

The next stop in the wire is the VR and it's about a foot away from where I am testing, so the drop at the VR will at best be 1.5v. I'm hung up on it because at that point it should be much lower and it is driving the alternator output up.I've cleaned and checked the ground on the VR, all is good there.

Because you are having so much trouble, I would not make assumptions. I WOULD at this point check right at the VR with a pin in the connector. And take a GOOD look at the VR connections. Are they tight, clean, bright?

You should be able to "follow back" from the drop with your meter

Heading towards the battery from the VR, it (originally)

went from the VR and junctioned at or near the bulkhead resistor

then went to the bulkhead connector

then to the ignition switch connector, and through the switch

then back OUT the switch connector on the battery feed wire

then to the ammeter and through it

then out the bulkhead on the red ammeter wire

then through the fuse link and to the starter relay

SO

Make a reading, one probe on battery, other probe on your VR IGN terminal

Move the battery probe to the red battery wire coming out the engine side of the bulkhead, where the fuse link goes through. Any change? I would doubt it

Clip your meter with an extension lead to the VR connection, so you can "get inside" the car

Check at the ignition switch connector. You want to check two connections, the battery coming into the switch, and the ignition run going out.

If you see a big change between the two, the problem is right there in the connector or the switch.

If they are both the same, the trouble almost has to be in the bulkhead connector terminals.

======================================


Since you have already pulled the bulkhead connector apart, you may have enough slack internally to release the bulkhead connector from the firewall and pull it loose and down. This way, you can use your meter to check BOTH the firewall side and the interior side of the connector.

 

[DionR]

I've done all of that, over and over and over again. And I continually get the same results.

From the battery positive post to the amp gauge -> .2v
From the battery positive post to power in at the ignition switch -> .6v
From the battery positive post to the blue wire out of the ignition switch -> .8v
From the battery positive post to the bulkhead connection of the blue wire -> 1.0v
From the battery positive post to the engine harness plug connection of the blue wire -> 1.2v
From the battery positive post to the alternator field connection of the blue wire -> 1.5v

And I've switched out or bypassed many of those things, with no change.

I thought maybe I had a broken wire in the section from the battery to the amp gauge, so I've bypassed that, too. I gotten to the point where I don't believe it is a power supply or resistance issue, and I can't find a ground issue either. What's left? Only thing I can think of is amps.

The formula for voltage drop is Vd = I*R. If R (resistance) is constant, then the only think that would increase Vd is more amps (I). Seeing that I have a constantly increasing voltage drop, I am left thinking that I must have a large amp drain instead of an increase in resistance.

But again, each time I think I am close, I end of with a black eye instead.

 

[67Dart273]

What have you done about improving the connectors?

Another thing you might do is to put an ammeter (your multimeter if it will measure that high) in series with the battery ground. BE CAREFUL. Get it all set up, make sure the dome lights and other loads are off, and key in "run"

Pull the battery ground, and hook your ammeter between battery NEG and engine block. This will tell you total circuit current. Next, pull off one field wire and notice difference in reading.

Might be time to find out where the harness splices the "ignition run" wire.

The "easy way out" is to cut the IGN wire coming out of the bulkhead, and run the VR and IGN off a relay fed from the starter relay. I thought I mentioned this, maybe not.

 

[67Dart273]

From the battery positive post to the amp gauge -> .2v
From the battery positive post to power in at the ignition switch -> .6v.

RIGHT THERE. You have a huge .4V drop between the amp gauge and the switch connector? HUGE HUGE red flag. Might be right at the ammeter connections or the IN HARNESS WELDED SPLICE

Check or remake the ammeter connections. These are molded eyelet ends and they can fail internally.

This splice is a factory welded splice in the black ammeter wire a few inches from the ammeter. You have to untape the harness, following the black wire to the splice.

From the battery positive post to power in at the ignition switch -> .6v
From the battery positive post to the blue wire out of the ignition switch -> .8v.

So add it up. You have .6V INTO the switch, and .8V OUT of the switch. That's .2V in and out of the switch, not too bad at all

From the battery positive post to the bulkhead connection of the blue wire -> 1.0v
From the battery positive post to the engine harness plug connection of the blue wire -> 1.2v
From the battery positive post to the alternator field connection of the blue wire -> 1.5v

.

With .8 out of the switch, and 1V at the bulkhead, again, just another .2V This is the firewall side of the connector? Not bad

BUT you are showing a TOTAL of .5V from the bulkhead to the alternator field?

(1.5 at the field subtract 1V at the bulkhead blue)

That's quite a bit. Might be a harness splice bad connection between the bulkhead, and the alternator / VR

 

[nm9stheham]

If I may chime in....

1) Dion, see if you can borrow another, higher quality voltmeter and re-try. I see you are using a cheap Harbor Freight meter. There are voltage fluctuations (ripple) on the alternator output and I would not be shocked if the cheap voltmeter was responding to peak or quasi-peak pulses on the system and giving exaggerated readings. Any 'ripple' on the charging current from the alternator will naturally increase as you move closer to the alternator. You need to be measuring the average DC drop and not any of the natural alternator ripple.

This is the one problem that I see with this type of test; the original meters used 'back in the day' when these tests were first developed for the Chrysler alternator systems were heavily damped analog meters.

After all, the 14.4 volts you see at the battery is not very high at all. So I am not so sure your readings are showing what is really going on.

2) It is critical that you do these tests with the battery IN GOOD CONIDTION AND FULLY CHARGED. That is the way these tests are set up for. If the battery is discharged, even partially, then the output of the alternator will be higher and the drops from the battery to the welded splice will be higher due to the higher charging current, and so will the field currents. After the battery has set disconnected overnight, what does it read? It should be at 12.6-12.7 volts; if not, it is not fully charged. (Or you meter is inaccurate!)

3) I would be improving the connections all along this path with silver loaded grease. This can make a really big difference. Car guys tend to not be so familiar with this stuff but it is perfect for this application. You can find it on ebay looking for silver conductive grease. (Don't get the silver thermal grease used for CPU heatsinks.) An example is MG Chemicals 8463-7G. (You can alos find a product called Cool-Amp which is rub-on silver plating powder to silver plate all connections but that is pricey.)

 

[67Dart273]

If I may chime in....

1) Dion, see if you can borrow another, higher quality voltmeter

I thought he told me he checked it against another meter, but I may be confused..............This is a good thought however

I thought he said 15.5 at the battery?

 

[nm9stheham]

15.5 was what he reported that he had originally after 1st fixing it but he got it down to 14.4; refer to the last part of the 4th paragraph or so in the original post. I assume that is stil lthe case.... ?? I did not read all the posts so you my have that right about a prior meter comparison.

 

[BillGrissom]

I agree w/ nm9stheham that the DC voltage you read on a multimeter is not always the full story, not when there are spikes or fluctuations on the wire. One sometimes must view it on an oscilloscope to get the true picture, but for you simply insure the VAC reading is low (indicating fairly steady). The alternator field current should be steady, if everything is working correctly.

You are incorrect that it switches on & off. That was with the mechanical contacts in early Vreg's (black rectangular box), and even most replacements for those today are transistor-controlled (like yours). The later type proportion the (steady) field current to control the alternator.

 

[DionR]

What have you done about improving the connectors?

Scrubbed/scratched/filed as able, sprayed down with an electrical cleaner and checked to make sure things are fully seated.

 

[DionR]

This splice is a factory welded splice in the black ammeter wire a few inches from the ammeter. You have to untape the harness, following the black wire to the splice.

I’ve untapped the entire harness, and then re-taped it, last summer. I looked at the welded splice, but in this case it is molded in rubber (or something), not just covered in tape.

Not ruling it out, just no way for me to visually check it. I did check for a high resistance through it and didn’t find anything.

So add it up. You have .6V INTO the switch, and .8V OUT of the switch. That's .2V in and out of the switch, not too bad at all

With .8 out of the switch, and 1V at the bulkhead, again, just another .2V This is the firewall side of the connector? Not bad

BUT you are showing a TOTAL of .5V from the bulkhead to the alternator field?

(1.5 at the field subtract 1V at the bulkhead blue)

That's quite a bit. Might be a harness splice bad connection between the bulkhead, and the alternator / VR

But if I am shooting for a .2v drop or less at the alternator, how can .2v through the ignition switch be ok? They all seem too high to me.

 

[DionR]

1) Dion, see if you can borrow another, higher quality voltmeter and re-try. I see you are using a cheap Harbor Freight meter. There are voltage fluctuations (ripple) on the alternator output and I would not be shocked if the cheap voltmeter was responding to peak or quasi-peak pulses on the system and giving exaggerated readings. Any 'ripple' on the charging current from the alternator will naturally increase as you move closer to the alternator. You need to be measuring the average DC drop and not any of the natural alternator ripple.

Ok, but the car isn’t even running when I am doing these tests, so there can’t be any ripples from the alternator since there is zero output.

After all, the 14.4 volts you see at the battery is not very high at all. So I am not so sure your readings are showing what is really going on.

I had forgotten that I had it down to that. The thing is, at that time (July of 2013) the amp gauge was showing about a +20 amp draw when the car was running and there was a 1.5v drop at the blue wire on the alternator. About a month ago I replaced the battery with a known good one and the amp guage started acting correctly, but the voltage across the battery is now showing the 15.5 volts.

2) It is critical that you do these tests with the battery IN GOOD CONIDTION AND FULLY CHARGED. That is the way these tests are set up for. If the battery is discharged, even partially, then the output of the alternator will be higher and the drops from the battery to the welded splice will be higher due to the higher charging current, and so will the field currents. After the battery has set disconnected overnight, what does it read? It should be at 12.6-12.7 volts; if not, it is not fully charged. (Or you meter is inaccurate!)

As of yesterday, it was showing 12.6v. And again, the car isn’t running when I am doing these checks, so there is no alternator output.

3) I would be improving the connections all along this path with silver loaded grease. This can make a really big difference. Car guys tend to not be so familiar with this stuff but it is perfect for this application. You can find it on ebay looking for silver conductive grease. (Don't get the silver thermal grease used for CPU heatsinks.) An example is MG Chemicals 8463-7G. (You can alos find a product called Cool-Amp which is rub-on silver plating powder to silver plate all connections but that is pricey.)

I will look for some of that. I thought to try something like that, but got worried that there was potential for crossing some circuits if grease got in areas I didn’t want it. Started planning to using a non-conductive grease to stop corrosion.

 

[DionR]

15.5 was what he reported that he had originally after 1st fixing it but he got it down to 14.4; refer to the last part of the 4th paragraph or so in the original post. I assume that is stil lthe case.... ?? I did not read all the posts so you my have that right about a prior meter comparison.

This is not the case any longer. This thread started in July of 2013.

It is currently running at 15.5v.

 

[DionR]

You are incorrect that it switches on & off. That was with the mechanical contacts in early Vreg's (black rectangular box), and even most replacements for those today are transistor-controlled (like yours). The later type proportion the (steady) field current to control the alternator.

Hate to disagree with you Bill. The following is directly from the FSM:
“Basically the electronic regulator operates as a voltage sensitive switch. There is a large transistor which is placed in series with the alternator field windings and a control circuit that senses the system voltage and turns the large transistor on and off as required. As the alternator speed and electrical system load changes, the control circuit is turning the transistor on and off many times per second almost all of the time that the vehicle is in operation.”

In addition, the testing procedure indicates that the green wire is removed from the alternator and a jumper from that field to ground is added. This maxes out the alternator so the output can be tested. This leads me to believe that the VR is the ground path for the field windings.

 

[DionR]

Got about an hour to mess with this this weekend with the following results.

Checked the voltage drop at the blue wire to verify what it currently was and got 2.0v. Pulled the blue wire off the alternator and got 1.0v. Checked other locations and all of the ones I check showed an improvement, but not enough for me to think there are no other issues.

The FSM indicates that I could check the amps that the field coil draws by connecting the battery positive post to one field wire connection on the alternator, the other one to the negative post through an amp gauge and then slowly rotate the alternator by hand. Expected reading is 2.5-3.1 amps. So, pulled the belt off the alternator, turned the key on with the blue wire connected (thereby connecting the battery positive post to the alternator) and then used my multi-meter to check amps between the battery negative post and the other field connection. The weird thing is, I didn’t have to slowly rotate the alternator to get a reading. Maybe it is just an extra step, and I did do it but didn’t see a difference. Result – 3.4 amps.

The FSM states a higher reading indicates a possible shorted rotor coil or grounded rotor.

So, checked to make sure one of the field coil connections weren’t shorted to ground and they seemed to check out ok.

Then I checked to see how much resistance there was in the field coil. The FSM shows the test being done after the alternator is disassembled by checking the resistance between the slip rings. I didn’t have my alternator even off the car, let alone disassembled, so I just checked using the field wire connections. I know this introduces the potential for resistance in the brushes to create a false reading, but I was hoping it wouldn’t throw things off too much. The expected reading is 2-3 ohms on a cold alternator, I got 11 ohms.

The FSM states that this indicates an open rotor, as opposed to a shorted or grounded rotor coil. Unfortunately, the above test indicating too many amps in the field coil seems to say the opposite. The mystery continues.

I plan to pull the brushes and try it again, but I suspect that there is a problem with the rotor and field coil in my alternator. Maybe not the entire problem I am dealing with, but I think it is part of it.

In no way am I saying I have an answer, nor that there can’t possibly be a wiring issue. Only saying my alternator doesn’t seem right and I need to get that fixed next.

 

[65-440]

I just went through this same exact problem, almost to a T ! Even to the point I was blowing headlamp bulbs. Had a big voltage drop in the ignition harness. Tried cleaning things up with no success. Ended up doing the madelectrical amp gauge bypass. Cured a lot of gremlins. Still had voltage issues. Changed alternator, voltage settled down at idle but still spiked high at RPM. Changed voltage regulator, been good since. So for me it took 3 different repairs. But did one at a time so I could see what changed with each Repair. Good luck!

 

[nm9stheham]

Dion, OK on the 15.5 volts. 3.4A vs just under 3 amps is not that big a difference. With 11 ohms there is no way to pull 3.4 amps! Ohms law wwoudl allow only a bit over 1A to flow through 11 ohms. So something is wrong. If you had an open in the field winding, you would get infinite or very high resistance readings.

And, the drop on the field wire per se is not what makes the VR push the alternator output high; it is the voltage on the pin into the VR itself; that power connection to the VR is the only point where the VR can 'sample' the system voltage. So your measurements to the field terminal on the alternator amy misleading; the measurements should be to the VR blue wire terminal.

The drop all depends on where the actual resistances are (as I am sure you know). I think it would be useful to move your test point to the VR connection. And, BTW, have you cleaned out that terminal? Those round terminals do get spread easily.

 

[DionR]

3.4A vs just under 3 amps is not that big a difference. With 11 ohms there is no way to pull 3.4 amps! Ohms law wwoudl allow only a bit over 1A to flow through 11 ohms. So something is wrong. If you had an open in the field winding, you would get infinite or very high resistance readings.

It's also contradictory that one test would indicate a potentially grounded or shorted field coil and the other one that it is open. Don't know.

The math doesn't work for the good values either, though. The expected 3 ohms would generate 4.2 amps (using a 12.6v battery), 2 ohms would be even higher at 6.3 amps, or the other way around it, the expected resistance should be between 4 and 5 ohms for a 2.5-3.1 range of amps. So I suspect that the one may not be directly related to the other in the field windings or something (there are other places Ohm's law does not apply). Not arguing with you, just saying that it might not be as easy as V=I*R. I don't pretend to know this stuff that well, so I might be missing something.

Really just don't know.

And, the drop on the field wire per se is not what makes the VR push the alternator output high; it is the voltage on the pin into the VR itself; that power connection to the VR is the only point where the VR can 'sample' the system voltage. So your measurements to the field terminal on the alternator amy misleading; the measurements should be to the VR blue wire terminal. The drop all depends on where the actual resistances are (as I am sure you know). I think it would be useful to move your test point to the VR connection.

Since the difference between the alternator connection and the VR connection is only about 12" of wire, and previous testing indicated the Vdrop only got worse the farther along the circuit I went, it made sense that the Vdrop at the VR would only be worse. Don't think it matters a whole lot if I measure 1.5v at the alternator or 2.0v at the VR, they are both way out of wack and something is wrong.

And, BTW, have you cleaned out that terminal? Those round terminals do get spread easily.

Yes, I've checked that connection and don't see an issue.

 

[DionR]

I just went through this same exact problem, almost to a T ! Even to the point I was blowing headlamp bulbs. Had a big voltage drop in the ignition harness. Tried cleaning things up with no success. Ended up doing the madelectrical amp gauge bypass. Cured a lot of gremlins. Still had voltage issues. Changed alternator, voltage settled down at idle but still spiked high at RPM. Changed voltage regulator, been good since. So for me it took 3 different repairs. But did one at a time so I could see what changed with each Repair. Good luck!

Glad to know I'm not the only one that has seen something similar.

 

[nm9stheham]

The point is that don't waste time worrying over an open winding; if it was open, no field current would flow ever and the alternator would not charge at all. (BTW, I have been in electronics for over 40 years.... an open winding won't read 11 ohms, and won't allow 3.4 amps to flow from 12v.)

OK on the VR connection; just wanted you to understand where the voltage counts and make sure you are not misleading yourself.

 

[DionR]

The point is that don't waste time worrying over an open winding; if it was open, no field current would flow ever and the alternator would not charge at all. (BTW, I have been in electronics for over 40 years.... an open winding won't read 11 ohms, and won't allow 3.4 amps to flow from 12v.)

So you don't think the alternator is faulty is some way?

 

[teringer]

I've been going through the same problem with a 73 duster, last week I had a weak spark and did the grounds check at the ign module pulled out the screw that holds the plug on the ign mod and replaced the blue box with a used one I had laying around. had good spark ect but my over charging problem was solved, it went from 16v to 13.8 I don't know if the power wire for the coil/ign box/alt wire are all on the same circuit, so I put the old one back in and it jumped back to 16v, anyway I ordered a new one and will see if it changes again.

 

[65-440]

So you don't think the alternator is faulty is some way?

Didn't think mine was either. Took it off and had my local rebuild shop test it, said it was working perfectly. Charge voltage was Almost 16V at idle. Replaced alternator, voltage at idle dropped to 13.5V. Something was Def wrong with the alternator. Give Mark a call at madelectrical, let him talk your ear off for a while. Very smart dude. Not saying you guys aren't smart here!

 

[65-440]

by the way, I did find a factory spec for voltage drop on the ignition harness .... up to 1V is acceptable. Seeing how I just went through this last month, I would say you have a component failure not wiring. The amp gauge bypass did help but did not solve my overcharge issue. For me it took multiple fixes for correct the problem. Pretty sure I could have gotten away with just replacing the alternator and regulator, not sure if one took out the other but they both were bad for sure. In the end the amp bypass has been more of a "piece of mind" thing.