Dual Field Alternator

Posted By: bronco9588

Dual Field Alternator - 05/04/13 01:34 AM

How does the Chrysler Dual Field Alternator work? What causes it to "turn off"/ "turn on" and go to full load?

The story behind this is that Mancini Racing sold me a "three-wire" alternator that is not a three wire alternator. I am very displeased with them and will not be doing business with them again. I am putting in a new wiring harness and need to make sure that I wire this guy correctly. Thanks.

Posted By: ahy

Re: Dual Field Alternator - 05/04/13 01:42 AM

On the alternator, have you requested exchange? I've dealt with Mancini a good bit and they handled a little "oops" promptly and correctly for me.

The alternator should have a post for the charge wire and two spade terminals for the wires that energize it and control output. The link from the archives shows the layout.

http://www.moparts.org/Tech/Archive/elec/21.html

Posted By: RapidRobert

Re: Dual Field Alternator - 05/04/13 01:56 AM

Quote:

I am putting in a new wiring harness and need to make sure that I wire this guy correctly. Thanks.

What make/year vehicle & how many terminals are on the the purchased alt? (1 large/2 small or 1 large/1 small)?

Posted By: bronco9588

Re: Dual Field Alternator - 05/04/13 03:50 AM

73 charger... one large and two small. Are the two smalls identical?

Posted By: RapidRobert

Re: Dual Field Alternator - 05/04/13 04:19 AM

Quote:

73 charger... one large and two small. Are the two smalls identical?

Yes, the 2 blue and green field wires can go on either alt male field terminal. Could you clarify more on what's the problem

Posted By: DAYCLONA

Re: Dual Field Alternator - 05/04/13 04:33 AM

Where Member 68HemiB when you need him,...this post is right up his alley, he's the authority on "dual field" alts

Posted By: 05dakota

Re: Dual Field Alternator - 05/04/13 12:50 PM

what is a none 3 wire alternator?

Posted By: therocks

Re: Dual Field Alternator - 05/04/13 01:06 PM

The regulator turns the Alt on and off.Battery charge and temp makes the demand of how much of a charge it puts out.73 would be a dual field alt.If you told them you wanted one for a 73 thats what it would be.The fields are basically the same.Rocky

Posted By: jlatessa

Re: Dual Field Alternator - 05/04/13 02:41 PM

On the same thread, does it really make any difference if your alternator puts out 15 volts unregulated?

When I had it checked, the store said "that's too high".

I thought the regulator determines the voltage going to your system.

Thanks, Joe

Posted By: John_Kunkel

Re: Dual Field Alternator - 05/04/13 06:34 PM

Quote:

How does the Chrysler Dual Field Alternator work? What causes it to "turn off"/ "turn on" and go to full load?

Battery voltage is applied to one field terminal on the alternator (usually a blue wire), the regulator supplies a variable ground to the second field terminal via a wire (usually green). The regulator senses the system voltage through the blue wire and adjusts the voltage by varying the ground in the green wire.

The only time the alternator will put out maximum voltage is if the battery is dead or there is a fault in the system, normally the output is in the 14V range.

Posted By: bronco9588

Re: Dual Field Alternator - 05/04/13 08:56 PM

So "on" would be 12volts, "off" would be nothing, and full load would be 0 volts on the sensing wire? Thanks.

Posted By: John_Kunkel

Re: Dual Field Alternator - 05/04/13 10:46 PM

There is no "on" or "off", the alternator always tries to put out more than battery voltage. The blue wire will always have battery voltage when the key is in the RUN position.

What we refer to as a 12V system is actually a 14V system (I'll probably get some disagreement here) but all of the components in a 12V system are built to handle 14V+.

Posted By: bronco9588

Re: Dual Field Alternator - 05/04/13 11:59 PM

So i purchased a wiring harness from rebel wiring. Anyways, the harness has a "alternator excitor" wire. I am assuming this supplies 12 volts (or 14) when the accessory bus is energied I.e. when the ignition is in run. I didn't want to damage anything as the voltage regulator would only sense 12 volts once the key is off start. It would "see" no volts until I let go of the key. Is this an issue?

Posted By: bronco9588

Re: Dual Field Alternator - 05/05/13 01:21 PM

Quote:

There is no "on" or "off", the alternator always tries to put out more than battery voltage. The blue wire will always have battery voltage when the key is in the RUN position.

What we refer to as a 12V system is actually a 14V system (I'll probably get some disagreement here) but all of the components in a 12V system are built to handle 14V+.

I'm pretty sure the regulator uses pulse width modulation to work... under your logic, if the alternator ever saw ground it would go to max current to try to get back to 14 volts. If it sees 14 volts it would reduce ampacity. What happens if it sees nothing... I.e. the wire is disconnected?

Posted By: RapidRobert

Re: Dual Field Alternator - 05/05/13 07:16 PM

Quote:

So i purchased a wiring harness from rebel wiring.

If your harness has a blue and a green field wire(s) with the female connectors plug them into both of the alt field terminals in either order & you're set. If that harness only has a green field wire (pre '70 harness) then plug it into either alt field terminal & ground the other alt field terminal to the alt case & with the large black charge wire with the ring terminal connected to the alt "batt" stud you are all set

Posted By: John_Kunkel

Re: Dual Field Alternator - 05/05/13 09:11 PM

The Rebel Wiring harness is pretty much the same as the factory except for ther wire colors. The "alternator exciter" wire is probably the same as the factory blue wire...it is powered only when the switch is in the RUN position; the "accessory bus" (?) plays no part in the charging system.

Posted By: John_Kunkel

Re: Dual Field Alternator - 05/05/13 09:12 PM

Quote:

I'm pretty sure the regulator uses pulse width modulation to work... under your logic, if the alternator ever saw ground it would go to max current to try to get back to 14 volts.

If the green wire is grounded, the regulator becomes ineffective and the alternator goes to maximum output which usually exceeds 15V. This is an all too common fault because the green wire usually runs along the valve cover where heat sometimes deteriorates the insulation and the wire goes to ground.

Quote:

If it sees 14 volts it would reduce ampacity. What happens if it sees nothing... I.e. the wire is disconnected?

If either field wire is disconnected there is no output from the alternator...the system reverts to battery voltage.

Posted By: bronco9588

Re: Dual Field Alternator - 05/06/13 01:27 AM

Quote:

The Rebel Wiring harness is pretty much the same as the factory except for ther wire colors. The "alternator exciter" wire is probably the same as the factory blue wire...it is powered only when the switch is in the RUN position; the "accessory bus" (?) plays no part in the charging system.

The harness is made up of 4 fuse boxes with 4 fuses each. Each "high" side of the fuse boxes are tied together and share the same voltage source. Two of the 4 fuse boxes are always on, one is on the start bus, and the last is triggered on "accessory" (which is on when the engine is running). The alternator exciter wire is located on accessory. Why, I don't know, but I don't think it matters much in this case. Might mean that I drain the battery if I am just listening to the radio or something?

Posted By: denfireguy

Re: Dual Field Alternator - 05/06/13 02:21 AM

Quote:

Quote:

There is no "on" or "off", the alternator always tries to put out more than battery voltage. The blue wire will always have battery voltage when the key is in the RUN position.

What we refer to as a 12V system is actually a 14V system (I'll probably get some disagreement here) but all of the components in a 12V system are built to handle 14V+.

I'm pretty sure the regulator uses pulse width modulation to work... under your logic, if the alternator ever saw ground it would go to max current to try to get back to 14 volts. If it sees 14 volts it would reduce ampacity. What happens if it sees nothing... I.e. the wire is disconnected?

Mopar alternators with electronic regulators did not employ pulse width modulation. Rather, the battery voltage through the ignition switch was fed to one terminal. The other terminal is connected to the diamond shape pass transistor on the regulator. It operates in linear mode. The output to the field wire can vary from about ten volts down to .7 volts. At .7 volts, the transistor is in full conduction. The .7 of a volt is the result of the junction voltage typical of a silicon transistor and that is as close to zero as it till get and the full battery voltage less distributed wire resistive loss and junction loss will appear across the field and maximum output is achieved.
Pulse width modulation works with square waves and generates massive amounts of electrical noise that would render that era's AM radios pretty unusable. I doubt Chrysler engineers even considered it.
Craig

Posted By: 68HemiB

Re: Dual Field Alternator - 05/06/13 04:54 PM

Quote:

Where Member 68HemiB when you need him,...this post is right up his alley, he's the authority on "dual field" alts