I am working on installing dual alternators on a 2005 LLY... The secondary alternator calls for an "charge on/off pin" in the ECM. Problem is, no one I've spoken with really knows the logic behind when/why the ECM drives that pin to command the secondary alternator to charge. If it's only when the electrical system pulls a certain amperage, I'd rather just let the secondary alternator charge whenever the primary is on... for the simple fact that two alternators working a light load together will prolong the life of both alternators... rather than loading up one all the time and rarely using the other.

Also, on the primary alternator, there are two pins... one I am assuming is the same as the single on the secondary... a "charge on/off pin". What is the second wire for?

And finally, the "battery not charging" message in the DIC... who knows why and how the ECM knows when to display that message? I've already figured it is not a drop in system voltage... because I've had that message on when one of my dual alternators was definitely charging...

Anyone who can shine a light on the mystery of the 2005+ LLY charging system gets a free cookie.

:)

No one likes cookies? :(

KB has a thread going on this issue. aybe you can help each other out.
Go to http://dieselplace.com/forum/showthread.php?t=49349

The only difference is that mine comes on and off randomly... and it doesn't go away depending on rpms...

I really wish someone could just shed some light on what the charging system is really doing as far as the 2 wires in the weather pack on the primary and the single wire in the weather pack on the secondary...

If your issue is the same as mine, the DIC will disappear if you unplug the secondary alt. I find that amperage comes from the primary, until plugging in the secondary, then all load shifts to it.

Backing up a bit. I have factory dual alts, which I have replaced with 145's, and the problem started wih that swap. I am thinking it might be a pin disparity between the 105 and the 145


It seems the warning is commanded when the primary does not supply amperage, as best I can tell.

Thank you "modified", maybe we can get this resolved soon.

Well, oddly enough, I have mine wired up a different way... I have the "charge signal" wire shared between the 2 alternators as I want the second running anytime the first one is... instead of letting the computer turn on the secondary whenever that may be...

Have you checked load on each alt?

Yes... I have a stock 105 in the primary position and a 180 in the secondary position. I have the same "charge" pin running to the secondary as the primary, so both should be running. However, at idle, with some normal things on like headlights, radio, etc... it pulls about 45 amps off the secondary. But hardly any from the 105... maybe about 5-7 amps. I'm wondering if because the secondary position is closer to the junction box, the secondary is just providing most of the power... I'm going to keep checking...

I think you violated a cardinal rule. Pretty sure they need to be identical.

Hmm... I wasn't aware that two power sources couldn't be different amperage. For example, if you replaced one of your 65amp/hour batteries with a 75AH... while the new battery has more capacity, it seems that it would work just the same...

Well, oddly enough, I have mine wired up a different way... I have the "charge signal" wire shared between the 2 alternators as I want the second running anytime the first one is... instead of letting the computer turn on the secondary whenever that may be...

That's the way mine is run, no problems with mine, but I do have identical alternators, if it matters (I wouldn't think so). I'd check for a loose connection at both alts. Those little pins that trigger the alt. are easy to expand out when you poke and prod them with a big test light. Unplug the connector(s) and use a small pick to squeeze the pin back into position. Where you made your splice, for the second alt., make sure that connection is tight. Intermittant problems are usually loose connection problems.

That second pin on the first alt. has always been a signal wire to tell you when the alt has failed (little batt light in the dash), on older diesels it is the signal that controls the tach on the dash.

Thanks for the info Rttoys... oddly enough, the battery light is getting less and less frequent... I drove 20 miles to work this morning, over about 30 minutes, and it came on just as I pulled in to park... but went away just as I stopped the truck and put it in park... its something strange, but I'm determined to figure it out. I'm going to double check my connections.

You know what's strange though... so if what you say is right, about the second wire being the one that flips the battery light (which is what happens, along with the DIC with the problem I'm seeing), it seems like it would only be the primary alternator that's wiggin out for some reason...

time to keep digging. I'm working on an inverter project, and I need to get this sorted out before I continue...

thanks for all the replies... anyone else?

That second pin on the first alt. has always been a signal wire to tell you when the alt has failed (little batt light in the dash), on older diesels it is the signal that controls the tach on the dash.

These as well, I believe. No?

the battery light is getting less and less frequent...

I find it is very random. The ECM probably needs to see low output for some time before it sends a warning. A guess. Wonder if there is a compator circuit.

I am certain, that the primary alt is the one and only one, that will cause a warning. If you lose the secondary, you will never know it, till the primary fails.

Try this and let me know

unplug both alts, start truck, verify DIC warning, plug in the primary, verify DIC warning dissappears, wait 10 secs, plug in the secondary.

Let me know.

Sure, that works exactly as stated... but I'll bet it throws the light again sometime soon. I'm starting to think that's why GM has it set for the PCM to turn on the secondary alternator only when current draw requires it... because as it stands now using the same "on" wire, I think the secondary is providing enough current to where the primary alternator is not having work much at all... signaling to the ECM (with its feedback wire) that it isn't charging... after all, when I checked the amperage on each alt. feed line, I was only seeing ~5 amps on the primary and ~30-40 amps on the secondary...

and why would the secondary get most of the workload if the same "on" wire is used with both? electricity follows the path of least resistance... the secondary is closer, with the same gauge/type wire, to the distribution block.

just a theory...

If the secondary alt has more available amperage then it may not have the ability to stut down as much as the weaker primary alt. You could always either swap the alts. around or change the signal wire from the primary to the secondary making everything backwards but reading normal.

I have been working on an idea that would let me combine the indicator wires into a logical "and" combination... where if one or both of the alternators wasn't driving its indicator voltage, the line would fail, causing the light and dic to activate.

But, that would still require the alternators to be close to the same amp rating... to avoid the problem I think I'm seeing with the primary not doing enough work to register as "charging".

I been thinking about it, and just swapping the alts. would probably be the easiest fix. (or worth a try). I don't worry about the light (older ones rarely functioned properly) just watch the guage.

The light? The constant "ding ding"

You know, that's odd... I haven't noticed the bell... I know any other time the DIC changes (like low fuel, for example) it dings... but not on "battery not charging"

So, I guess it's just physics as to why the alternators won't just "balance"... which ever one is easier to pull current from (as in closer to the distribution box, larger wire, less resistance, etc...) its going to... until some point the other will begin to help as the load becomes greater.

Are you going to try my procedure? It worked for me. I just tested my loads, they are even on each alt.

Sure, that works exactly as stated... but I'll bet it throws the light again sometime soon.

Yeah, I walked out and tried it right after you mentioned it... I don't have my amp clamp with me, so I couldn't check the loads on each... but I've got a long drive home tonight, so I'll get to see if the light comes on or not... and when I get home, I'll clamp it to see if the loads are about even.

Thanks!

I find it is very random. The ECM probably needs to see low output for some time before it sends a warning. A guess. Wonder if there is a compator circuit.

I am certain, that the primary alt is the one and only one, that will cause a warning. If you lose the secondary, you will never know it, till the primary fails.

I don't guess I've asked this the entire time... are you using the same "on" wire for your secondary as you are the primary?

I don't think there would be a comparator circuit as both alternators power the same distribution box... and there is no feedback mechanism on the secondary alternator....

are you using the same "on" wire for your secondary as you are the primary?

..

I do not know. It is dual from the factory.

In that case, I'm almost certain your "on" wire on the secondary goes to a totally different connection on the ECM... pin 57 on the C2 connector... Which, if your measurements are correct as far as seeing equal load on both, then I may just connect mine the same way. I was under the assumption, however, that the ECM only drove the secondary alternator when the primary became fairly loaded... which to me, sounded like a good way to burn out the primary and never use the secondary...

then again, if there is no warning for the secondary going dead, that is a better idea. The secondary would last forever, and be a reliable backup.

This continues to be a question in my mind. It just doesn't makes sense to have dual alts, and no warning for #2. Good going GM. Saved 10 cents.

I don't understand why your's is not working properly and mine has been fine for the last 7 months.

Not too sure... it seems as if the distribution box is going to pull from the path of least resistance... and based on the fact that the primary wire on each is identical, except for length, the secondary is supplying most of the power, as it is shorter... may be wrong, but for now, without further testing, this appears to be the case.

The path of least resistance, that your talking about, is so minimal I can't see that being the case. I'm still thinking it has something to do with the secondary alt being srtonger than the primary. Kind of like having twin engines on a boat but one is a 125hp and the other is 250hp. If both engines are throttled the same the 250 will quickly over power the 125 making the 125 almost useless. That is why I thought of swapping alts (for sh!ts and grins), so the ecm sees the higher amperage on it's origonal wiring and then the weaker, now, secondary can sit a idle until needed and all is well.

Not too sure... it seems as if the distribution box is going to pull from the path of least resistance... and based on the fact that the primary wire on each is identical, except for length, the secondary is supplying most of the power, as it is shorter... may be wrong, but for now, without further testing, this appears to be the case.

You are driving me crazy. :) Did my idea work for you?

also with 4 gauge running 30 amps, there is no appreciable resistance difference between a 1 foot and 3 ft cable. Not even measurable.

:cookoo: Sorry...

Yes, I'm sure I've mentioned several times that I've tried your idea... and it still does the same thing. I hear you are working on an A/C power project... we should converse as I'm doing something similar... once I get my charging system under control :)

I just am using mine as a backup home generator, utilizing a hefty inverter. That was the project. Also for use as a field power supply. I changed the 8 gauge alt wires to 4 gauge, and now that my loads appear to be balanced, I'm ready for disaster.