Voltage regulator - quick question

[osufans]

So my battery light came on again, and now it's staying on. You can hear the blower motor speed up and slow down, so it sounds to me like the voltage regulator is flaking out. I stopped and had it tested again, and they said the battery is fine, but it is not charging.

I have been told you have to replace the entire alternator....does anyone know a workaround? Seems ridiculous to me to replace the entire alternator just to fix the voltage regulator...but whatever.

Thanks for any quick replies, as I will be needing to fix this no later than tomorrow afternoon.

Thanks!

Matt

 

[jnaut]

I'm confrused... isn't the Voltage Regulator part of the PCM?

How did you test your charging system?

Also, alternator's easy to remove on the KJ, remove it and take it down to Napa or some such place to have it tested.

 

[LibertyTC]

x2 as above.
Proper testing for the entire charging system comes from dealer or shop that has a star scan OBDIII and can read the PCM and can also check the output from alt.

 

[jnaut]

You can do a quick test on your charging system by sticking a meter on the battery and after starting the engine, the voltage should run up to about 14.xx volts.

While I've read on this forum that it's not entirely reliable, my jeep has never not jumped to 14.xx volts when first turning over the KJ, so if I suspected a charging problem and it didn't jump to 14.xx volts and remained at 11.9-12.5 volts or so, I'd be pretty concerned there was a problem.

 

[osufans]

done the "quick test", or at least I'm guessing that's what the auto store does...they hooked a meter up, tested the battery, then ran a diag while the jeep was running.

both parts stores i spoke with said the voltage regulators are integrated with the alternator. i'm still not entirely sure how these newer systems work, but it makes no sense to me that the PCM would be regulating the voltage, at least not internally. they may somehow be controlling the amount of charge, but the voltage regulator itself should be part of the alternator.

 

[jnaut]

According to the 02-07 Jeep Liberty Factory Service Manual:

CHARGING SYSTEM
DESCRIPTION
The charging system consists of:
† Generator
† Electronic Voltage Regulator (EVR) circuitry
within the Powertrain Control Module (PCM)
† Ignition switch
† Battery (refer to 8, Battery for information)
† Battery temperature sensor
† Generator Lamp (if equipped)
† Check Gauges Lamp (if equipped)
† Wiring harness and connections (refer to 8, Wiring
for information

It goes on:

The amount of DC current produced by the generator
is controlled by the EVR (field control) circuitry
contained within the PCM. This circuitry is connected
in series with the second rotor field terminal
and ground.

I don't know if the alternator has any separate circuitry of its own which may act in addition to, or independently of the PCM. If this internal piece of the alternator was bad, then my guess is you're in for an alternator swap. Further meaning that it irrelevant whether or not it's the "voltage regulator"-- you need a new alternator.

Mind I'm not suggesting you need an alternator (although I suspect it) I'm just relaying what my understanding of the FSM is telling me.

By the way, KJ throwing any codes?

 

[osufans]

when i take my old one out, i'll see if i can inspect it more closely. from all the info i've found so far, it appears the voltage regulator is part of the alternator, but somehow the PCM may be tied into it.

i'd be willing to bet dollars to donuts that the voltage regulator is built-in to the alternator.

 

[jnaut]

when i take my old one out, i'll see if i can inspect it more closely. from all the info i've found so far, it appears the voltage regulator is part of the alternator, but somehow the PCM may be tied into it.

i'd be willing to bet dollars to donuts that the voltage regulator is built-in to the alternator.

As I say, there may be a separate discreet voltage regulator within the alternator-- I'll let our ******** board experts weigh in on that (although the FSM doesn't mention it).

But my point is, even if there is a separate component with in the alternator, I'll bet dollars to donuts that it's a "non-user servicable part" and you're still in for a whole new alternator.

It's not that I want this to be the solution out of some sense of vindication, I'm just trying to help.

Do let us know what you find.

 

[osufans]

i didn't check for codes, just got a battery light, so i didn't even think to do the key dance.

i'll have to check. allpar.com has some info that is inclining me to see what you're referring to, regarding the PCM regulator. i'm still not exactly sure how or why they would put the regulator on the PCM, but i guess i'll find out.

 

[jnaut]

Modern technology is my guess. If you put the voltage regulator as part of the computer, it can more finely tune the charging system based on other sundry inputs (like battery temperature) to achieve a more balanced system-- or actuate "limp modes" with the 25% duty cycle as the KJ does, as opposed to the old days when alternators were probably either ON or OFF whenever there was demand on the system.

Just a guess, though.

 

[osufans]

is it possible, and this is just me thinking out loud here....that the voltage regulator is still in the alternator, however the duty cycle is what is controlled by the PCM? from what i've been reading, it almost sounds like that's the case. there was one article about grounding out the green wire briefly, which is the ground field wire, to see if that causes a spike in voltage, which would indicate that the alternator is still functional. it appears to me that this may be all that the PCM manages.

 

[jnaut]

For what it's worth, OSUfans:

OPERATION
The amount of DC current produced by the generator is controlled by EVR circuitry contained within the Powertrain Control Module (PCM). This circuitry is connected in series with the generators second rotor field terminal and its ground. Voltage is regulated by cycling the ground path to control the strength of the rotor magnetic field. The EVR circuitry monitors system line voltage (B+) and battery temperature (refer to Battery Temperature Sensor for more information). It then determines a target charging voltage. If sensed battery voltage is 0.5 volts or lower than the target voltage, the PCM grounds the field winding until sensed battery voltage is 0.5 volts above target voltage. A circuit in the PCM cycles the ground side of the generator field up to 100 times per second (100Hz), but has the capability to ground the field control wire 100% of the time (full field) to achieve the target voltage. If the charging rate cannot be monitored (limp-in), a duty cycle of 25% is used by the PCM in order to have some generator output. Also refer to Charging Operation for additional information.

 

[osufans]

For what it's worth, OSUfans:

lol....i think we may have found the answer.

 

[tjkj2002]

The voltage regulator is 100% contained in the PCM.

If the voltage regulator was part of the alternator there would only be one wire going to the alternator besides the main power wire.

 

[osufans]

The voltage regulator is 100% contained in the PCM.

If the voltage regulator was part of the alternator there would only be one wire going to the alternator besides the main power wire.

Well, I took mine apart, and the voltage regulator is 100% contained in the alternator.

Let's think about it....how the heck are you gonna run 135 Amps through the PCM, back to the battery?

The amount of charge is regulated by the PCM, via a switched relay in series with the ground field, which is a wire coming off the voltage regulator, INSIDE the alternator. However, the charge is directed through a cable that is routed back to the battery.

I was not able to get any part #'s off the voltage regulator, and it looked like more of a pain than it would be worth anyways trying to get it apart and replaced. It was definitely much easier to just replace the whole alternator and been done with it.

For a better description, see: http://www.howstuffworks.com/alternator.htm

 

[tjkj2002]

Well, I took mine apart, and the voltage regulator is 100% contained in the alternator.

Let's think about it....how the heck are you gonna run 135 Amps through the PCM, back to the battery?

The amount of charge is regulated by the PCM, via a switched relay in series with the ground field, which is a wire coming off the voltage regulator, INSIDE the alternator. However, the charge is directed through a cable that is routed back to the battery.

I was not able to get any part #'s off the voltage regulator, and it looked like more of a pain than it would be worth anyways trying to get it apart and replaced. It was definitely much easier to just replace the whole alternator and been done with it.

For a better description, see: http://www.howstuffworks.com/alternator.htm

hardly any amps run through the voltage regulator,better read up on what a VOLTAGE regulator does,it's not a amperage regulator.The only place you will see the high amps is the main power wire from the alternator to the battery and the battery to the starter.

The diodes and rectifier bridge is in the alternator but the voltage regulator is in the PCM.2 completely different things,even know what a rectifier bridge does?

That link is a very basic understanding and 99% of the time is totally wrong for modern charging/electrical systems,pretty true for the '80's and '90's though.

 

[jnaut]

Well, I took mine apart, and the voltage regulator is 100% contained in the alternator.

Let's think about it....how the heck are you gonna run 135 Amps through the PCM, back to the battery?

edit: the sentence in red should be taken with a grain of salt as I'm not 100% sure what levels of current the PCM will pass through it. However, the FSM pretty crystalline in its explanation of the voltage regulator housed in the PCM.

You don't. It's a voltage regulator, not a current regulator. It regulates the voltage read from the battery. The PCM doesn't have to pass 135 amps of current through it. As the FSM stated above, the EVR (Electronic Voltage Regulator) is entirely contained in the PCM.

Also as I stated above, there may be some discreet circuitry inside the alternator which takes cues from the EVR in the PCM and then does some sort extraneous regulation within the duty cycle as dictated by the PCM, but as I had bet, it would be a "non-user servicable part" and you'd still end up replacing the alternator.

What this leads us to is an interesting discussion as to what would happen if you could disconnect the PCM from the alternator and bypass the PCM altogether for your charging.

From my read of the FSM, the PCM would think that the charging system had failed and switch to "limp in" mode which would then try to put the alternator in a 25% duty cycle. But being entirely disconnected from the alternator, this would essentially become a phantom operation.

In theory, you could put solar panels on the top of your Jeep, put an inline voltage regulator and that would become your charging system (for daytime driving only, natch).

Glad you got your problem solved.

 

[osufans]

Well, say what you will...here's another picture that looks similar to our Jeep's, showing the voltage regulator as part of the alternator. I still say that the voltage regulator is built-in, and the only thing the PCM does is regulate the charge cycle.

http://www.autoshop101.com/trainmodules/alternator/alt109.html

Oh and by the way, yes, I took engineering in college, so I do know a thing or two about voltage and current (Ohm's law anyone?)

 

[tjkj2002]

Well, say what you will...here's another picture that looks similar to our Jeep's, showing the voltage regulator as part of the alternator. I still say that the voltage regulator is built-in, and the only thing the PCM does is regulate the charge cycle.

http://www.autoshop101.com/trainmodules/alternator/alt109.html

Oh and by the way, yes, I took engineering in college, so I do know a thing or two about voltage and current (Ohm's law anyone?)

That pic looks nothing like the KJ's alternator.

What you are seeing is the rectifier bridge,not a voltage regulator.If I could somehow post the wiring diagram from my '02/'03/'04/'05/'06/'07 FSM(yes I have all of those on my labtop) for the charging system you would see clearly where the regulator is,that being in the PCM.

 

[jnaut]

Well, say what you will...here's another picture that looks similar to our Jeep's, showing the voltage regulator as part of the alternator. I still say that the voltage regulator is built-in, and the only thing the PCM does is regulate the charge cycle.

http://www.autoshop101.com/trainmodules/alternator/alt109.html

Oh and by the way, yes, I took engineering in college, so I do know a thing or two about voltage and current (Ohm's law anyone?)

Well, ok, we'll say what we want, and I guess the Chrysler Factory Service Manual kind of says the same thing we're saying.

I think where we're getting bogged down here, OSUfans is the fact that there exists vehicle specific functions which are separate or outside generic alternator functionality. Do a google search on 'voltage regulator PCM' and you'll find a wealth of posts indicating that most modern cars do voltage regulation through the PCM. Random hit:

http://www.cumminsforum.com/forum/94-98-non-powertrain/14631-alternator-voltage-regulator.html

Hi my 96 amp metor gauge is about at 12.5 volts until I get up to 55mph. What I would like to no is there a voltage regulator, or is it built into the alternator. thanks

The regulator is built into the PCM (computer) and costs $500 plus to replace.

Once you are certain the problem isn't the alternator or batteries you can disconnect the PCM regulator and use an external one. It's easy, cheap and won't effect anything else. Any 12 volt regulator will work. Remove and tape the small wires on the alt replace as in the picture below. Make certain the switched positive is at the top of triangular connector, the other two wires are interchangeable. The regulator doesn't have to be like the one below, in fact the number on it is no good.

wll i disconneted the batteries and the truck died . looks like i need a alternator.

Don't be so sure. The alternator is just the slave, without the PCM to make it charge it sits cold. Unhook the two small field wires located on the back of the alternator attached with 8mm nuts. Keep them away from grounding on the block etc. Attach two jumper wires, polarity doesn't matter...one to each stud, then the other ends to positive and the other to negative. This will full field the alternator and bypass the regulator. I wouldn't hook up the jumpers until the truck is running. It will display full output so don't leave it that way but for a couple of seconds. Voltage can go sky high by full fielding. Once you have done this, leave the truck running and using a voltmeter check for voltage acrosss the terminals you took off. One wire is pos and the other neg, you should see between 7-12 volts. This will tell you the PCM is supplying field voltage and current to the alternator. In which case keep looking. If the alternator didn't labor the engine, or show high voltage on a meter, it is most likely short on brushes. If it did, well keep looking again.

I wouldn't go throwing an alternator at it until you've diagnosed it down a little further. Taking off the batt cables is not a good thing to do to modern charging systems, and it still doesn't tell you the problem with the charging system.