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Discussion Starter · #1 ·
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.

:)
 

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Discussion Starter · #2 ·
No one likes cookies? :(
 

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Discussion Starter · #4 ·
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...
 

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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.
 

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Discussion Starter · #6 ·
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...
 

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Discussion Starter · #8 ·
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...
 

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Discussion Starter · #10 ·
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...
 

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Commissioner Gordon
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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.
 

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Discussion Starter · #12 ·
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?
 

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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?
 

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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.
 

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Discussion Starter · #16 ·
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...
 

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Commissioner Gordon
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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.
 

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Discussion Starter · #18 ·
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".
 

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Commissioner Gordon
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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.
 
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