PDA

View Full Version : Proper Voltage at Alternator Field Control Terminals?


EMSJEEP
September 9th, 2017, 16:32
Should they both be 12v+? Is one low voltage or ground? 2001 XJ

I'm putting out 4v from the alternator at idle, which is killing the battery.

Thanks

trippled
September 9th, 2017, 17:11
IIRC, one is power and one is a ground. Don't forget to voltage drop your chargeback wire and grounds.

EMSJEEP
September 9th, 2017, 17:16
I have 12.5v at one (I have significant voltage drop across my battery isolator) but the other does not appear to be ground. I think I'll run an independent ground direct to the battery and see if that helps. I.e. If it's supposed to be a ground, then it's blown and hopefully that's my problem. The nuts on the terminals had worked themselves almost completely off when I went to check, cleaning and tightening didn't help though...

8Mud
September 9th, 2017, 18:03
Voltage *in* is constant voltage, typically (near) battery voltage, dark green/orange wire.

The alternator regulates on the ground side, dark green wire.

Typically a voltage drop on the green wire, depends on how it is regulating at the moment.


Grounding the green wire can smoke your alternator.

EMSJEEP
September 9th, 2017, 18:09
Voltage *in* is constant dark green/orange wire.

The alternator regulates on the ground side, dark green wire.

Typically a voltage drop on the green wire, depends on how it is regulating at the moment.


Grounding the green wire can smoke your alternator.

K, so won't do that....

So when I put red probe on right and black probe on left, I get nothing, red probe right and black probe to bony gets 12.5v, red probe to left and black probe to body gets either 0 or a low voltage (like 3v)

8Mud
September 9th, 2017, 18:24
I haven't worked on a 2001 specifically, but the basics seem to be the same. I use the wire colors instead of left or tight or the pole number.

On mine 96 I get battery voltage on the green orange and around 9 volts on the green, The green side depends on whether the battery is (near) full and if it is right after startup or after the motor warms up.

If you are getting battery voltage to the orange/green wire to ground and have a reasonable voltage drop from the green wire to ground, you are likely regulating. If the voltage is the same it is likely either an open wire or the PCM isn't regulating.

EMSJEEP
September 9th, 2017, 18:47
I have nothing or almost nothing on one terminal and a constant 4v out to the battery from the large lug.

8Mud
September 9th, 2017, 18:47
Sounds like you have an open field winding. Take the wires off and ohm between the two field winding posts on the alternator.

General Tip, double check all readings, try different ground points. Oil, rust, dirt or whatever can mess up your readings, clean shiny metal or strat to battery negative are the safe points (usually).

8Mud
September 9th, 2017, 18:56
I have nothing or almost nothing on one terminal and a constant 4v out to the battery from the large lug.

Reading that large lug doesn't tell you much, it can either be the alternator output or the battery voltage. It isn't a one way wire.

Try an ohm test on one or both of the field wires to the case and see if there is a short.

Could be your alternator, could be our PCM/voltage regulator, could be the wiring. Guessing gets real expensive real quick.

Kind of sounds like you have an open circuit in your field winding (just a guess). Which could be a bad alternator or the connection at the plug. I'm not sure of the setup on the 2001, but is it possible somebody over tightened the nuts onto the field winding poles and broke studs off inside the alternator?

techno1154
September 9th, 2017, 19:04
I do not know the wire colors on the 2001 XJ, but this is how it work on the 1996 XJ:

Dark Green and Orange (DG/OR) from the ASD (Automatic Shut Down) relay and provides 12 volts to the alternator when the ignition is on.

Dark Green (DG) is the field driver. It provides a negative to the alternator field wire to control the voltage coming from the alternator to the system. The field driver is PCM controlled. The PCM pulses the negative on and off in an attempt to keep the voltage level within specs.

When testing the alternator in the XJ, I attach a wire to this terminal and with the engine running temporarily touch the other end of the wire to a clean ground and monitor the voltage at the battery. With a good alternator, the voltage could quickly climb past 16 volts.

EMSJEEP
September 9th, 2017, 19:06
Reading that large lug doesn't tell you much, it can either be the alternator output or the battery voltage. It isn't a one way wire.

Try an ohm test on one or both of the field wires to the case and see if there is a short.

Could be your alternator, could be our PCM/voltage regulator, could be the wiring. Guessing gets real expensive real quick.

Kind of sounds like you have an open circuit in your field winding (just a guess). Which could be a bad alternator or the connection at the plug. I'm not sure of the setup on the 2001, but is it possible somebody over tightened the nuts onto the field winding poles and broke studs off inside the alternator?

Mine is on a diode for the battery isolator

8Mud
September 9th, 2017, 19:17
Mine is on a diode for the battery isolator

Do you have dual batteries, why the isolator?

8Mud
September 9th, 2017, 19:41
I do not know the wire colors on the 2001 XJ, but this is how it work on the 1996 XJ:

Dark Green and Orange (DG/OR) from the ASD (Automatic Shut Down) relay and provides 12 volts to the alternator when the ignition is on.

Dark Green (DG) is the field driver. It provides a negative to the alternator field wire to control the voltage coming from the alternator to the system. The field driver is PCM controlled. The PCM pulses the negative on and off in an attempt to keep the voltage level within specs.

When testing the alternator in the XJ, I attach a wire to this terminal and with the engine running temporarily touch the other end of the wire to a clean ground and monitor the voltage at the battery. With a good alternator, the voltage could quickly climb past 16 volts.

If the green wire is pulse your meter may not read it, some do, some don't, depends on the frequency of the pulse. If you have an analog meter you may get different results. Just a thought. I have two VOMs and a couple of old analog meters, when I get a really funky reading I swap out meters. Make sure you are trying to read the DC position and not the AC position on your meter. And just for giggles switch over to the AC node and see what you read, bad diodes can cause some odd readings.

EMSJEEP
September 9th, 2017, 20:06
Do you have dual batteries, why the isolator?

Yeah, house batteries in the trunk for HAM radio, emergency lighting and compressor on a 5 gal tank

8Mud
September 9th, 2017, 20:22
Yeah, house batteries in the trunk for HAM radio, emergency lighting and compressor on a 5 gal tank

Isolator is usually wired between batteries and not between the alternator and the batteries? Though with a 4 volt output on your main cable this is unlikely to be the issue IMO.

I don't really know the setup for a 2001, but on mine the alternator main power out cable goes to a junction on the side of the PDC and then jumps to battery positive. A side note, if yours does have the junction, check the nut for tightness.

Do you have a stock Denso alternator? That four volts on the main power out from the alternator sure sounds like a generator reading, if in fact that cable is isolated. But don't let me confuse the issue, just thinking out loud. The residual magnetism in the field winding magnets will give you four volts if the field current is interrupted, this is only on a true generator with field magnets, not an alternator.

How are you doing your tests, the engine has to be running. And how does it run on four volts? Something isn't adding up here or I'm confusing myself. :)

8Mud
September 9th, 2017, 21:00
My bad, I looked up how the newer isolators are wired, they have a diode on both battery legs.

Best guess is an open or shorted field winding. Second best guess is a faulty regulator or wiring. A faulty rectifier is unlikely but possible, one way to test for this is to switch your meter over to AC mode, some meters will pick up a failed diode in the rectifier.

Your field winding may be open where you mentioned the nuts being loose on the alternator connector. Is it possible you spun one of the field winding pole studs and messed up the connection, just a wild guess?

EMSJEEP
September 9th, 2017, 21:11
Isolator is usually wired between batteries and not between the alternator and the batteries? Though with a 4 volt output on your main cable this is unlikely to be the issue IMO.

I don't really know the setup for a 2001, but on mine the alternator main power out cable goes to a junction on the side of the PDC and then jumps to battery positive. A side note, if yours does have the junction, check the nut for tightness.

Do you have a stock Denso alternator? That four volts on the main power out from the alternator sure sounds like a generator reading, if in fact that cable is isolated. But don't let me confuse the issue, just thinking out loud. The residual magnetism in the field winding magnets will give you four volts if the field current is interrupted, this is only on a true generator with field magnets, not an alternator.

How are you doing your tests, the engine has to be running. And how does it run on four volts? Something isn't adding up here or I'm confusing myself. :)

Its a Powermaster 170 amp alternator. I ran it fine for about 6 years on the setup with the isolator. The Jeep sat without running for a year and I'm coming off of that right now.

In total it has new mains as well to run the upgraded alternator and accessories .

The isolator has an "Alternator In" Lug, and a "Battery 1 Out" and a "Battery 2" out lug. Between the Alternator lug and the Alternator sits a 200amp circuit breaker. Mine does not go to the PDC, but there is a jumper from the PDC to Battery 1 (under the hood) which supplies vehicle power.

I got the Jeep running again last week after a new CPS sensor, fuel pump and a bunch of other housekeeping after being not turned on for over a year. It has been out of regular service since 2012.

Once I got it running last week I let it run for a few hours without difficulty, then left it for a week, when I came back, it started up again just fine and I left it to idle for a few hours. When I got back, it hadn't burned much fuel and the battery was dead, so I think it cut off within an hour or so of when I started it to let it run. I recharged the battery off of an AC charger and started it again, let it run, it died a few minutes later. I had bought a new Odyssey battery anyway, so I threw that in thinking that the 3 yr old battery that has sat for a while was maybe not good enough to run off of. So I put the new Odyssey in and it started fine and ran. I started checking with a DMM to see what was up and noticed that at the lug on the back f the alternator and grounded to battery negative, I was only getting 4 VDC and that the battery voltage was steadily dropping from 13.0VDC to 12.4VDC.

So, I've been running the Jeep a few minutes at a time to check things out, but not dipping below 12.3 on the new battery, and charging it up with the 6 amp AC trickle charger between attempts.

EMSJEEP
September 9th, 2017, 21:13
My bad, I looked up how the newer isolators are wired, they have a diode on both battery legs.

Best guess is an open or shorted field winding. Second best guess is a faulty regulator or wiring. A faulty rectifier is unlikely but possible, one way to test for this is to switch your meter over to AC mode, some meters will pick up a failed diode in the rectifier.

Your field winding may be open where you mentioned the nuts being loose on the alternator connector. Is it possible you spun one of the field winding pole studs and messed up the connection, just a wild guess?

When I noticed things weren't working, I checked the terminals and the nuts were hanging near the ends of their threads and the rings barley making contact. I hadn't touched them in years before it stopped working. I don't think they are close enough to cross each other, but it's possible. I tightened them down but didn't really wrench on them.

EMSJEEP
September 9th, 2017, 21:16
Just went out again. Steady 12VDC to one terminal and the other is jumping all over on my meter, but a steady ~3v at the battery out lug.

8Mud
September 9th, 2017, 21:28
Just for the heck of it, switch your meter to AC volts and check that alternator to isolator circuit again. A faulty rectifier may show up as AC voltage on some meters.

Do the ohm test on your field windings,

Double check your voltage on the regulated side of the field winding circuit to a good ground (with the engine running), pretty sure it is the solid green wire. If it is the same voltage as the in wire (orange/green) you likely have a regulator issue. If there is no voltage you likely have a winding or no power in issue.

Check the voltage at the field winding in wire orange/green with the engine running.

If things get too crazy you may have to pull the alternator and take it in for a bench test. A real pain. If it is the regulator you may have pulled the alternator for nothing. I don't envy you all the crawling around.

EMSJEEP
September 10th, 2017, 09:01
Reading 4 VAC on the alternator to isolator. 3VDC. From battery ground to the field terminals I have battery voltage at one and 1.5-0 VDC at the other while battery voltage sits at 12.3 VDC

techno1154
September 10th, 2017, 10:38
Reading 4 VAC on the alternator to isolator. 3VDC. From battery ground to the field terminals I have battery voltage at one and 1.5-0 VDC at the other while battery voltage sits at 12.3 VDC

Anything could have gone wrong over the time the XJ was not running including the alternator and the isolator. My recommendation would be to remove the isolator completely from the system and check only the battery (one battery) and the alternator. Connect the alternator output wire to the PDC or to the battery + and battery + to the PDC.

Start the engine and bring it up to about 1,500 RPM then trouble shoot the charging system. The alternator functionality could be checked at this time by employing the method I mentioned in my previous post. With a volt meter attached to the battery terminals + and - look for 16 volts. If 16 volts is present the alternator is good and the PCM is bad. If no 16 volts then the alternator is bad.

You did mention you had loose wire/nut I think on the alternator? Why don't you check all wires on the alternator? I would recommend removing and cleaning them then securing them properly. Also, check for +12 volts on that OR/GR wire at the alternator stud when the engine is running. The alternator will not work if it do not receive voltage on this terminal. Did you check all ground wires in the engine compartment? Give them the once over for peace of mind.

EMSJEEP
September 10th, 2017, 18:33
So, nothing worked, nothing produced results. In a moment of red neck anger, I figured that the lose terminals probably crossed and shorted, so I quickly grounded the green wire, nothing there either.

Then I got mad, like, $500 broken alternator mad, and I was like "to hell with you alternator" and I hit the green wire with 12.5v from the battery. Boom, alternator kicked on, brought me up to 14.5v and settled around 14.25/.15 at the isolator and about 13.7 at the battery. Ran it for about 45 minutes watching the voltage on the DMM and everything appears to be operating correctly.

Dunno why that worked, but, it did

techno1154
September 11th, 2017, 15:25
So, nothing worked, nothing produced results. In a moment of red neck anger, I figured that the lose terminals probably crossed and shorted, so I quickly grounded the green wire, nothing there either.

Then I got mad, like, $500 broken alternator mad, and I was like "to hell with you alternator" and I hit the green wire with 12.5v from the battery. Boom, alternator kicked on, brought me up to 14.5v and settled around 14.25/.15 at the isolator and about 13.7 at the battery. Ran it for about 45 minutes watching the voltage on the DMM and everything appears to be operating correctly.

Dunno why that worked, but, it did

That is good that it works. Some things are unexplainable. Keep your eyes on it for a few trips to ascertain it is stable.

EMSJEEP
September 11th, 2017, 20:11
That is good that it works. Some things are unexplainable. Keep your eyes on it for a few trips to ascertain it is stable.

My electrons got stuck...


Will keep an eye on it, and I think some liquid electrical tape on those terminals too.:explosion

EMSJEEP
October 20th, 2017, 16:22
Looks like its not working again...spoke to the techs at Powermaster and they think PCM.

Original question still stands I guess, whats the proper exciter voltage from the PCM?

Jeep Driver
October 20th, 2017, 16:28
Should be 12v

lawsoncl
October 21st, 2017, 14:56
Looks like its not working again...spoke to the techs at Powermaster and they think PCM.

Original question still stands I guess, whats the proper exciter voltage from the PCM?


As I recall, you should have battery voltage to one side of the field coil and the PCM controls the GROUND for the field coil. It pulses it, so it's hard to read with a voltmeter. As others mentioned grounding the wire that goes to the PCM should kick the alternator to full output. If it's not doing that, then the alternator has a probkem. Also, if the PCM is not trying to ground it, and the voltage on the ground wire is low then it may throw a code for a bad field coil (might also throw a code if the field coil looks right but the battery voltage isn't changing).

https://w05.dealerconnect.chrysler.com/service/mds2002/serviceInfo/en_US/81092f02.gif