Dual Field Alternator: Swapping the Field Wires

On a Mopar style dual field alternator, what happens when you swap the field wires from the stock setup?

The reason that I ask is because when I took my Mopar square back alternator (left below) into NAPA to have it tested, they tested it as the chart shown and it failed due to lack of voltage. Then I handed them my Powermaster (right below) unit and they hooked it up the same way as the square back and the machine told them to swap the field wires. Once they swapped the wires, then it tested PERFECT.
I just received an email from Powermaster discussing my current ammeter/voltage guage fluctuating at idle and they are suggesting that I swap the field wires.
Why would they suggest this and why did the PM alternator test fine at NAPA after they swapped the field wires? I have been running this alternator for a year now (wired like my stock unit) with no issues until a few weeks ago. I am just trying to understand the suggestion.

EDIT:
This is the response from Powermaster as to why to reverse the field wires:

""All the field wires do is complete the circuit, so it shouldn't matter if you reverse them. It really shouldn't do anything different, but I've seen it work in cases like these. It could be a sign that the diodes are starting to go out, but I've also seen this work, and work for years.""

I have had more discussions with them and since the machine at NAPA said to reverse the field wires, he thinks that the diodes may be the issue even though the machine showed the alternator to be in perfect condition after the swap. I am going to swap the field wires and see if it makes a difference at idle. If it does, Powermaster will take it in for repair and return it to me as new condition. Even if swapping the wires does not work, I will probably send it to them anyway due to the NAPA machine test and I am not out any driving time due to our Winter weather.

Thanks

Attached picture 7001567-PM_SB.JPG

Posted By: NachoRT74

Re: Dual Field Alternator: Swapping the Field Wires - 01/05/12 04:53 AM

one more to chime in to say

ITS THE SAME no matter what. If there was a diff, you'll have some label at housing, or some ANTI IDIOT connector at brushes

Posted By: a12rag

Re: Dual Field Alternator: Swapping the Field Wires - 01/05/12 05:27 AM

Guys . . .remember that the field is setting up a magnetic field that the rotor (connected to the shaft which is turned by the belt) moves around. It needs a ground connection and positive connection. The voltage regulator senses the output voltage and varies the amount of voltage and current going to the field.

The stator is the stationary coil of wire around the outside of the rotor. As the rotor turns, the magnetic field induces current in the stator wires - although it is producing alternating current (AC, which goes positive and then negative, just like in the house), in what is called 3 phase (house is single phase).

Since the current is alternating between negative and positive, you have to use diodes to rectify the current into DC (direct current) that is used in the car. With 3 phases, you need 3 positive and 3 negative diodes. When you combine the output of each 3 diode sets, you then have 12volt DC current output from the alternator. This is a more efficient producer of electrical energy than a generator - i.e. it puts out current at low rpm (like at idle), that is why it was a standard years ago.

So with the single wire field alternator, one of the field connections was directly connected to ground and the other to positive from the voltage regulator.

For the dual wire field alternator, one wire (positive) is connected to the ignition circuit, and then the other wire is connected to the voltage regulator - which then varies the amount of current via resistance to ground.

You can test your alternator yourself (briefly), by putting battery positive to the field wire from the alternator (usually a blue with white tracer) and then ground the other field terminal. You should see FULL output and charging on your ammeter (if you still have one) . . . . if this is the case, then you have a bad regulator. If not, then get another alternator. Needless to say, this is with the engine running.

I have also heard of taking a screwdriver (metal one) and holding it to the back of the alternator, where the rear bearing is. If it is held in place, then the alternator is working, as a magnetic field is present from the rotor.

So the back to the question at hand - why would reversing the field wires on the test stand make a difference ??? You are basically causing the rotation of the magnetic field to be set up 180 degrees out - doesn't matter much as you are rectifying the AC signal back to DC through the diodes, however, you are getting one set of diodes working before the others. But it really doesn't matter, so long as you have output from the alternator

Hope that makes it all clear as mud . . .

Cheers

Mark

Posted By: 63stabamatic

Re: Dual Field Alternator: Swapping the Field Wires - 01/05/12 01:17 PM

I agree, swapping the field wires should make no difference if the alternator is working correctly. One set of diodes is slightly different than the other. FWIW A lot of rebuilt alternators, starters,etc get right back out there as the original problem was never found. Just had another "new rebuilt" alternator go bad on a car I just bought, looked brand new but was intermittent after warm-up. I have a local outfit here that rebuilds alternators and starters, been using their Bosch alternators on my Mopars for 20 years, never a problem.

Posted By: YO7_A66

Re: Dual Field Alternator: Swapping the Field Wires - 01/05/12 01:55 PM

"" I agree, swapping the field wires should make no difference if the alternator is working correctly.""

I think that "WORKING CORRECTLY" is the key.

I witnessed what the test machine had the operator change to make the alternator test correctly. Since the alternator tested good after the field wire swap on the machine, I am assuming that since I have already swapped the field wires (temporary jumpers) that the next time I start up the engine, the ammeter/battery volt gauge may not show the bouncing issue.

Posted By: MoparforLife

Re: Dual Field Alternator: Swapping the Field Wires - 01/05/12 02:03 PM

As far as that goes an alternator don't care which way it turns either. (Other than the cooling fins)

Posted By: NachoRT74

Re: Dual Field Alternator: Swapping the Field Wires - 01/05/12 06:22 PM

no matter the fields order, as far you get magnetic field inside. Then stator captures the sine power ( alternate power ) and diodes bank takes the sine section variation what it cares ( positive section or negative section of the sine ) to feed the + and - busses ( stud or chassis ) No matter with section of the sine signal it happens first

so no matter either the rotor direction as stated, the important thing here is create the magnetic field at rotor

Posted By: YO7_A66

Re: Dual Field Alternator: Swapping the Field Wires - 01/05/12 06:28 PM

Lets say that the alternator does work correctly after swapping the field wires (as shown on the test machine), would you send it in to be rebuilt or see how long it runs?

Thanks allot for the replies.

Posted By: NachoRT74

Re: Dual Field Alternator: Swapping the Field Wires - 01/05/12 06:34 PM

if is in guarantee I will give to manufacturer. No headaches about something recently paid.

since I'm overseas, send to manufacturer IS THE HEADACHE so I would take care by myself.

soooo, all depends on your position

Posted By: Cab_Burge

Re: Dual Field Alternator: Swapping the Field Wires - 01/05/12 06:42 PM

I see one thing missed on this dicsusion, you have two different field feeds, maybe one of them has a problem on it in the connectors or corrosion or

I have seen a bad connector on one of the the feild input wires (It had broken most of the wires at the connector, maybe it had one or two still flowing current, not the entire bunch of wires like it should have been) cause charging problems. The feed wires are 18 gauge if I'm remembering correctly

I replaced that connector and it got ALL BETTER

Lots of gremlins out there of all kinds for Murphy to use to test us against our troubling shooting skills

Posted By: YO7_A66

Re: Dual Field Alternator: Swapping the Field Wires - 01/05/12 06:45 PM

I am just outside of the warranty period but the manufacturer said that they would cover labor and if parts were minimal, they would take care of that too and retest it and send it back to me as new. This is why I am leaning towards sending it back and just waiting for the rebuild rather than taking my chances during my driving season.
PM said that they have seen the wires swapped and then ran for years, but I am not that confident on electrical parts these days. I have had toooo many new electrical parts failures in the last year. (Powermaster Alternator, FBO ignition box, Mallory E-coil, and a FAST wideband controller (twice) all in the last year. These are some big names in the industry and I alone have had these failures.)

I will be able to have the dash back in this weekend (headlight switch issue) and then I will retest the alternator.

Cab,
I removed both field wire connectors due to loose connections and replaced them with new connectors and squeezed the female ends until both were very snug.
thanks

Thanks again.

Posted By: NachoRT74

Re: Dual Field Alternator: Swapping the Field Wires - 01/05/12 06:56 PM

Quote:

I see one thing missed on this dicsusion, you have two different field feeds, maybe one of them has a problem on it in the connectors or corrosion or I have seen a bad connector on one of the the feild input wires (It had broken most of the wires at the connector, maybe it had one or two still flowing current, not the entire bunch of wires like it should have been) cause charging problems. The feed wires are 18 gauge if I'm remembering correctly I replaced that connector and it got ALL BETTER Lots of gremlins out there of all kinds for Murphy to use to test us against our troubling shooting skills

I told him by email couple of days ago ( he contacted me ) that it could be one of the brushes making bad contact with rotor trace. Some overheat could melt partially the brush isolator and make an erratic brush contact OR a rotor axle play or bad setting making warp the isolator so then getting stuck the brush inside the isolator. That it happened to me twice with the vertical brush. Thas is a BIG posibility.

BTW, being out of warranty I will fix by myself FIRST. Fortunatelly alternators are cheap and easy fix.

I would begin checking the brushes isolators AND isolation. The psoition where the ammeter senses spikes could be that BY CASUALITY the wire with ground is being plugged on a bad isolator getting then full negative field. And when conecting positive there maybe is not bad enough to cause a short ?

You tell me about bad electronic quality controls... 2 MP chromed ECU boxes, One Ready to run MSD dist ( of a friend of mine ) what was sent for fix to MSD ( overseas ) and returned BAD again... etc...

Posted By: denfireguy

Re: Dual Field Alternator: Swapping the Field Wires - 01/06/12 04:07 AM

If the machine knows the wires are backwards, there almost has to be a short to ground somewhere.
The machine applies 12 volts to the field on one wire and grounds the other. If there was a short, the logic in the tester would see that short and assume the person hooking it up did it wrong. When he reverses it, the shorted field connection is now hooked to the machines ground. The logic now sees a complete circuit with a good ground and less current draw on the 12V feed. Machine is happy, the alternator tests good. Unfortunately, because of the internal short, it will not work right in the car going to full output at all times. Powerquest is right, the alternator is bad and as I suspected, the parts store testers do not fully test dual field alternators.

Posted By: RapidRobert

Re: Dual Field Alternator: Swapping the Field Wires - 01/06/12 01:29 PM

Quote:

What Denfire said

As Double R would say ding ding ding we (may) have a winna

Posted By: NachoRT74

Re: Dual Field Alternator: Swapping the Field Wires - 01/06/12 04:55 PM

talking about what I was told about the brush isolator melted getting stuck the brush... found a malfunction on my alt and look what I found:

( after fix this, mounted back the alt, worked great for 10 minutes and broken again... the rotor went bad. It's open. )

Attached picture 7004260-lafoto(13).jpg

Posted By: YO7_A66

Re: Dual Field Alternator: Swapping the Field Wires - 01/06/12 09:34 PM

""The machine applies 12 volts to the field on one wire and grounds the other. If there was a short, the logic in the tester would see that short and assume the person hooking it up did it wrong. When he reverses it, the shorted field connection is now hooked to the machines ground. The logic now sees a complete circuit with a good ground and less current draw on the 12V feed. Machine is happy, the alternator tests good. Unfortunately, because of the internal short, it will not work right in the car going to full output at all times. Powermaster is right, the alternator is bad and as I suspected, the parts store testers do not fully test dual field alternators. ""

Excellent description. Thank you.

I have already made arrangements with Powermaster and the alternator is going back next week for a full test and rebuild.

Thank you to all.

Posted By: YO7_A66

Re: Dual Field Alternator: Swapping the Field Wires - 01/07/12 10:03 PM

""Unfortunately, because of the internal short, it will not work right in the car going to full output at all times.""

I swapped the field wires to see if the ammeter/voltage guage changed, and as mentioned above, it acted the same with the wires swapped.
The alternator is off and in a box waiting to be shipped back for repair.

Thanks again to all.

Posted By: Yancy Derringer

Re: Dual Field Alternator: Swapping the Field Wires - 01/13/12 10:17 PM

Other than a short in the field circuit, there is ONE other remote possibility. Since some of these aftermarket units may well come from (cough, gag) questionable sources, it just might be that the METALLIC ALLOY of the rotor core is not what it should be. It MIGHT just be that some units RETAIN MAGNETISM far better than they should, and that when reversing the field, the residual magnetism in the core (at least for a short time) will be "fighting" the polarity of the field due to the swapped field connections.

Back in the days when rebuilders were "cheapy" modifying older frames for isolated field, I used to see a fair number that were mistakenly grounded.

Posted By: YO7_A66

Re: Dual Field Alternator: Swapping the Field Wires - 01/19/12 12:34 PM

The alternator is currently at Powermaster and they have been testing it and they can not make it fail.

Review:
The test machine at NAPA told the technician to reverse the field wires to be able to complete the test.
My ammeter fluctuates at idle and up to about 1500rpms, then it smooths out after 1500rpms. It did not do this until my last drive of the season. My system voltage jumps back and fourth from 13-15 volts while the ammeter is fluctuating. A new voltage regulator showed the same results.

I am trying to give them all of my info so they can keep checking it but I am not sure what else to tell them before they try and send it back to me. Is there another type of voltage regulator that I can test? My current two are the NAPA brand. I do have a Chrysler BLUE (constant output) regulator that I could test if needed.

Any suggestions are appreciated.

Posted By: RapidRobert

Re: Dual Field Alternator: Swapping the Field Wires - 01/19/12 02:16 PM

Quote:

My ammeter fluctuates at idle and up to about 1500rpms, then it smooths out after 1500rpms. My system voltage jumps back and fourth from 13-15 volts while the ammeter is fluctuating. A new voltage regulator showed the same results.

Any suggestions are appreciated.

Not an (electronic) reg problem

Posted By: YO7_A66

Re: Dual Field Alternator: Swapping the Field Wires - 01/19/12 02:37 PM

They just told me that they are getting constant voltage output with the field wires wired per stock. They are swapping the field wiring to see if they can get the voltage to start fluctuating.

Thanks

Posted By: BigTerry

Re: Dual Field Alternator: Swapping the Field Wires - 01/19/12 04:31 PM

wouldn't changing the field wires change the polarity of the voltage? + to -?

Posted By: MoparforLife

Re: Dual Field Alternator: Swapping the Field Wires - 01/19/12 04:38 PM

Quote:

wouldn't changing the field wires change the polarity of the voltage? + to -?

Posted By: NachoRT74

Re: Dual Field Alternator: Swapping the Field Wires - 01/19/12 04:50 PM

wires to brushes gives fields to create ALTERNATED CURRENT ( hence the alternator name ) by sine waves produced by the + and - fluctuations when rotor spins, creating magnetic fields what stator captures. Then Diodes hooked up to stator take care of take the correct polarity of the waves to stud and chassis, becoming on DC ( direct current )

since we are talking about - and + fluctuations on sine wave, doens't really matter what happens first on the sine wave, if - or + section of the wave.

Posted By: Sparky77

Re: Dual Field Alternator: Swapping the Field Wires - 01/19/12 05:38 PM

I ussally test mine by grounding out one of the wires going to the regulator

LETS TAKE THIS #$^&&*#@ OUT AND SEE IF WE CAN GET IT TO DRIP PARTS
Sparky
72 CUDA 440 10.10 1/4
72 Challenger 340 Rallye..sunroof car

Posted By: YO7_A66

Re: Dual Field Alternator: Swapping the Field Wires - 01/19/12 06:22 PM

I am afraid that they are not going to find anything wrong and then I am back to step one on trying to figure out what is causing the ammeter/voltage fluctuations.

If it does come back with no issues, then I am planning on pulling one fuse at a time while watching the ammeter/voltage gauge to see if I can locate a circuit that clears it up.
I was also thinking of buying a cheap stock alternator to test on the car too to see if there is any change.

Thanks for the replies.

Posted By: Sparky77

Re: Dual Field Alternator: Swapping the Field Wires - 01/19/12 07:57 PM

i have found in the past that a bad regulator or a poor ground on the regulator to body can cause that....check all grounds that seems to be something thats always under rated .... body to motor a quick jumper to the motor to body will tell you
Sparky

LETS TAKE THIS #$^&&*#@ OUT AND SEE IF WE CAN GET IT TO DRIP PARTS
Sparky
72 CUDA 440 10.10 1/4
72 Challenger 340 Rallye..sunroof car

Posted By: YO7_A66

Re: Dual Field Alternator: Swapping the Field Wires - 01/19/12 08:12 PM

Sparky,
The VR is bolted into the firewall in the stock location. Both of the mounting bolts have ground wires going to different grounds in the engine compartment. I can take a voltmeter and put the "+" lead on the "+" battery post and the "-" lead on either one of the VR mounting screws or the VR ground strap (just below the connector), and I get a battery reading.
Thank you for the reply.

Posted By: denfireguy

Re: Dual Field Alternator: Swapping the Field Wires - 01/19/12 08:23 PM

Quote:

wires to brushes gives fields to create ALTERNATED CURRENT ( hence the alternator name ) by sine waves produced by the + and - fluctuations when rotor spins, creating magnetic fields what stator captures. Then Diodes hooked up to stator take care of take the correct polarity of the waves to stud and chassis, becoming on DC ( direct current )

since we are talking about - and + fluctuations on sine wave, doens't really matter what happens first on the sine wave, if - or + section of the wave.

Exactly right. Except in Australia where the car keeps trying to drive on the wrong side of the road and the fields should be changed.
Seriously, even if you turned the alternator backwards, the full wave rectifier bank will produce the proper voltage polarity.

Posted By: YO7_A66

Re: Dual Field Alternator: Swapping the Field Wires - 01/20/12 01:26 AM

My dash lights and my dome lights are fluctuating with the ammeter/voltage gage. Would the dash voltage regulator affect the ammeter/battery voltage reading if it was bad?

What about a bad battery?

Thanks again. Just thinking out loud.

Posted By: Rick_Ehrenberg

Re: Dual Field Alternator: Swapping the Field Wires - 01/20/12 02:41 PM

Quote:

Powermaster's observation is correct; if swapping the field wires changes the output, the alternator is faulty...even if it works that way.

Exactly. That would be conclusive proof of field-coils(rotating)-to-ground current leakage.

This kind of stuff shows up more and more as the "cores" get older. Good rebuilders use an instrument called a Hi-pot to check for leakage, but don't count on that.

This is why the all-new alternators, even though Chinese, are probably a better bet (Autozone Duralast Gold, etc.)

Rick

Posted By: 68HemiB

Re: Dual Field Alternator: Swapping the Field Wires - 01/20/12 05:35 PM

Quote:

Maybe Moparts member 68HemiB will chime in, he's an xpert on "dual field" alternators and their inner workings

I know it's been almost two weeks, but I cannot let Mike down on this point.

Most knowledgeable folks on moparts will cringe when they see someone use the term posi when applied to a limited-slip differential installed in a Mopar.

Well, it's like fingers on a chalkboard to me when I read "dual field". An ISOLATED FIELD alternator as is being discussed here might have two field connections, but there is but a single field circuit inside the alternator.

Please stop it, everyone.

Dual Field Alternator: Swapping the Field Wires