testing voltage regulator

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gniknayrb18

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ok im having charging issues...none is the issue...let me start with what all i have going on under the hood...72 dodge demon 340 optima red top battery have a msd 6al, msd blaster 2 coil oem voltage regulator and have the mad set up for my ammeter. ok whlie running...have to jump it off...im getting 12.4 volts at battery(positive-neg terminal).. from neg terminal- blue wire (which i think is ign 1) 12.4 vltz. from neg terminal- green wire ( should be ign 2) i am getting 4.4 vltz) i have had the alternator checked and it is good. when i noticed it not charging i had it checked then went to the voltage reg and noticed that it was loose from the fire wall one of the screws backed out so i took it off and wire brushed the case and fire wall to create a better ground and its still doing the same thing. is it possible that with it becomming ungrounded it could of damaged the voltage regulator
 
from neg terminal- blue wire (which i think is ign 1) 12.4 vltz.

This seems good

from neg terminal- green wire ( should be ign 2) i am getting 4.4 vltz)
This is at the green wire at the alternator and still connected? This measurement may not mean much

voltage reg and noticed that it was loose from the fire wall ............... is it possible that with it becomming ungrounded it could of damaged the voltage regulator

It might be possible

Alternator problems that is a "no charge" condition boil down into several areas..............

1...An open or poor connection in the charging line to the battery, especially in unmodified cars

2...bad alternator

3...Problems in the field wiring harness and connections

4...Bad regulator

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

To start, determine if 1 or 2 is the problem. Take a clip lead, remove the green field wire from the alternator, and clip the alternator terminal which you just exposed to ground. With the key "in run" check voltage to ground at the blue connection. Do not unhook it, rather, "back probe" the connection. With the area in subdued light, and key "in run" connect / disconnect the clip lead. You should see a small spark. Start the engine, slowly bring up RPM while watching a voltmeter on the battery.

If voltage can be made to climb (keep below 16V) then the alternator is OK

If not..........double check that with key in "run" and the green wire grounded that you have battery voltage at the blue field wire. You can also check field current by putting your meter from the green wire field terminal to ground. Post brand and model (or a photo) of your multimeter if you don't know how

Also if not, check that the output wire to the battery is OK. With engine running as before, and clip lead installed, check battery voltage, and voltage at alternator output stud. If the voltage at both is the same, and low, the wiring is OK. But if battery voltage is low, and the alternator stud fluctuates a lot, going way high, above 15V then the output wire is open

If voltage DID go up, now your problem is in field wiring or the regulator. You've alreadly checked the blue wire. With engine and key off, use ohmeter to check disconnected green wire from alternator end to the regulator connector. Should be good continuity. That is the only place the green wire goes.

With regulator connector disconnected, and key in "run" check voltage at the blue terminal in the connector. Should be "same as battery." Inspect the connector. Work it in out several times off the regulator to scrub the terminals. Make SURE the regulator is grounded.

If it does not charge, replace the regulator
 
Here is a simplified diagram from MyMopar

As you can see, the green wire only goes one place..........from one alternator field up to the regulator

The blue is switched 12V from the key, and feeds the remaining field, and the regulator

The green basically controls "the amount of ground" on the field. When you clip the green alternator to ground you are causing full battery field current, some call this "full fielding" This should cause full output on a good alternator.

Dual_Field_Alternator_Wiring.jpg
 
There is a way to bench test a regulator. It requires a variable voltage power supply, voltmeter, and a 50 Ohm resistor. The resistor serves to limit current in the field connection for test purposes. I use 0 to 30V supply, with a 0 to 3A current limit, it has built-in voltmeter an ampmeter. The regulator is powered from the supply, connect the regulator case to the - of power supply, the (I) terminal of the regulator to the + of the power supply. Also connect one lead the resistor to the +, and the other lead to the (F) terminal. Connect the voltmeter + to the (F) terminal and the - to ground. Start the powersupply at 12V, the voltage, at the field should be less than 1.5 Volts, increase the power supply voltage to around 13.8V, the field terminal voltage will rise immediately, and follow the supply. Do not go higher than 15V.

The voltage point where the F goes high is the voltage where the regulator regulates. A voltage below, turns a transistor on, sinking the field to ground, the other field lead is high so the field is energized. The alternator increases voltage, the F terminal goes high, reducing field current. In normal operation, it toggles at a high frequency as needed to regulate.
 
hi there I need help really bad.ive been working on this 78 midnite express for 5 years
This seems good

This is at the green wire at the alternator and still connected? This measurement may not mean much



It might be possible

Alternator problems that is a "no charge" condition boil down into several areas..............

1...An open or poor connection in the charging line to the battery, especially in unmodified cars

2...bad alternator

3...Problems in the field wiring harness and connections

4...Bad regulator

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

To start, determine if 1 or 2 is the problem. Take a clip lead, remove the green field wire from the alternator, and clip the alternator terminal which you just exposed to ground. With the key "in run" check voltage to ground at the blue connection. Do not unhook it, rather, "back probe" the connection. With the area in subdued light, and key "in run" connect / disconnect the clip lead. You should see a small spark. Start the engine, slowly bring up RPM while watching a voltmeter on the battery.

If voltage can be made to climb (keep below 16V) then the alternator is OK

If not..........double check that with key in "run" and the green wire grounded that you have battery voltage at the blue field wire. You can also check field current by putting your meter from the green wire field terminal to ground. Post brand and model (or a photo) of your multimeter if you don't know how

Also if not, check that the output wire to the battery is OK. With engine running as before, and clip lead installed, check battery voltage, and voltage at alternator output stud. If the voltage at both is the same, and low, the wiring is OK. But if battery voltage is low, and the alternator stud fluctuates a lot, going way high, above 15V then the output wire is open

If voltage DID go up, now your problem is in field wiring or the regulator. You've alreadly checked the blue wire. With engine and key off, use ohmeter to check disconnected green wire from alternator end to the regulator connector. Should be good continuity. That is the only place the green wire goes.

With regulator connector disconnected, and key in "run" check voltage at the blue terminal in the connector. Should be "same as battery." Inspect the connector. Work it in out several times off the regulator to scrub the terminals. Make SURE the regulator is grounded.

If it does not charge, replace the regulator
 
hi there,I need help ,ive been working on restoring a midnite express for 5 years,shes almost done,install a efi from msd a 6a box,started it this weekend,i cant get it to charge,can you help me please,evrything is brand new top to bottom
 
hi there,I need help ,ive been working on restoring a midnite express for 5 years,shes almost done,install a efi from msd a 6a box,started it this weekend,i cant get it to charge,can you help me please,evrything is brand new top to bottom


You need to start a new thread. And you are going to have to give us more details about your wiring, AKA what is factory what is not, and what you've added, and what you have for an alternator and regulator
 
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