220 amp alternator

[Chuck FB]

13 hours ago, Another JR said:

The 100 amp fuse is on the battery interconnect wire. If you have the second alternator, it would be connected to the aux battery via a larger fuse that is not on my fuse block. 
 

The 30 amp fuse and wire go to the trailer 7 pin connector hot pin. 

I stand corrected in what this two alternator system is doing when I open the door, it was dropping in voltage as well which surprised me as I had been checking before but perhaps not soon enough after the door was shut and the truck powered back down. Anyway I had the multi meter attached to the aux battery before I opened the door and propped up on the back of the hood by the windshield and sure as ****** .. open the door and the voltage drops off, then I put the truck into "run" mode by holding the button for the aprox 5 seconds and then the voltage goes down even further. Then got back out of that mode and started the truck and the voltage really dropped as it was cranking and once started it popped back up to above 12 volts but was not charging, that took quite a few seconds before it started responding and eventually climbing up above 14.5 as a peak and then settled back to 14.5 or so and then checked both batteries as the truck was running and they were both about the same as they were being charged. So somehow there is a tie in there even if the truck is not set to accessory but just merely opening the door. Yet if I try charging the main battery the aux does nothing ( I thought I had tested it by using a charger on the aux and checking the main battery for a voltage increase as well ).

 

There definitely are two alternators on this truck, not just on the window sticker ... but actually living under the hood. I assume the main one is the one on left side of the engine as one is standing in front of the truck looking at the engine layout, the aux alternator sits lower down on the right side under the power steering reservoir and therefore closer to the aux battery. I didn't attempt yet to see where the 100 amp fused cable runs to though, its rather busy with power steering lines etc and was more concentrating on finishing the engine oil change and greasing the truck and staring into each pleat of the oil filter to see what horrors I might find.

[Chuck FB]

On 4/3/2025 at 10:03 PM, Another JR said:

I have the single 220 amp alternator and the factory installed optional auxiliary battery. There is an isolator relay that connects the batteries when the ignition is on. There was another thread recently where some of us were discussing exactly how it worked. It’s a dumb (meaning not smart) system, and the batteries are simply connected when ignition is on. No time delay. The aux battery therefore contributes some current to the starter, limited by the resistance of its charging wire, which has a 100 amp fuse on it. I measured the aux battery voltage while cranking and it dropped. 
 

The attached picture shows the aux battery fuse block with the isolator relay. 

I finally spotted where the power cable comes from the 170 amp alternator as a silver heat wrapped wire bundle that passes by and then under the alternator was in the way to block my view and just confused me. So there is a cable that connects to the alternator stud with the special insulated black nut just like the main alternator has ( you can look at your alternator for reference ) and that cable simply comes up and Tee's into the main cable that attaches to the fuse box. If you see in your own photo where your single cable enters under the fuse box cover, well with this setup they terminate that same cable to the fuse box with a more elaborate end so that this secondary alternator cables own end has a place to bolt onto the main fuse boxes cable and then they have a little plastic cover where it Tee's together since its live after all and it states on the top of that little square cover "not for jump start" as it would be too easy to clamp onto that assembly as a power source and blow the main fuse at the main battery is what I suspect. So from what I see the two alternators can't help but be tied together all into the same charging system. Unless I am missing something it would sure appear as though its able to feed over into the main battery, the question would be if the main alternator crapped out internally. if the secondary alternator would seamlessly take over the full load.  If there was some truth to this 170 amp alternator having some fancy system within it to spin freely until enough demand is called for, I don't know as it sure doesn't look like anything special from the outside.

 

And as I said before about using a charger on the main battery with the doors closed and the truck in its normal off mode, the voltage did not feed through to the aux battery. What I tried now was to put a substantial charger on the main battery and opened the door but with the key far away from the pickup and no change. Then put the truck into the accessory position with the key present and that must have triggered the isolator relay as the aux battery was now receiving charge, same when I put the truck into the run mode without the truck running. I would take it from that, as long as the truck accessory is off and an RV was plugged in it could only draw from the aux battery, however if the truck was turned onto accessory, then both batteries would be connected and the RV would be drawing from both batteries and draw them both down.

 

It would be nice to find some official info on the system to know for sure that lets say both alternators are in fact charging at all times and sharing the load as a total 390 max rated output system.

 

By the way as per the uniqueness of the system via parts in stock, the dealer did not have that belt in stock for the two alternator system and had to order it for me so I at least have my hands on a spare. Possibly the aftermarket may do better in stocking it, its hard to say. So that is one negative among others in having a two alternator system for sure, lack of parts in stock and more expensive when things go wrong.

[Chuck FB]

On 4/3/2025 at 10:03 PM, Another JR said:

I have the single 220 amp alternator and the factory installed optional auxiliary battery. There is an isolator relay that connects the batteries when the ignition is on. There was another thread recently where some of us were discussing exactly how it worked. It’s a dumb (meaning not smart) system, and the batteries are simply connected when ignition is on. No time delay. The aux battery therefore contributes some current to the starter, limited by the resistance of its charging wire, which has a 100 amp fuse on it. I measured the aux battery voltage while cranking and it dropped. 
 

The attached picture shows the aux battery fuse block with the isolator relay. 

I took a photo of the two battery/two alternator setup and had all the covers taken off so where the second alternator tee'd into the main harness to the fuse box shows. Its in the garage and used a flash so not the best photo but can zoom it in and make out how they tied in. The little square cover over that termination I unclipped and shoved off to the side and that odd substance on the terminals is fluid film to maybe help with salt that will be misting around in the future unfortunately. The cable from that second alternator comes up from the bottom of the photo and bolts onto that fancy looking terminated end that the main cable from the main battery is crimped onto and then that whole thing bolts onto the fuse box stud.

 

Edited April 12, 2025 by Chuck FB

[redwngr]

2025 3500 battery/alternator ordering possibilities

 

 

 

 

Notes 1 and 2 on Alaskan Snowplow edition refer to WT  (1) and LT (2). Ut's not available on LTZ and HC 

 

 

 

Others are all trims, but have engine choice requirements

Edited April 12, 2025 by redwngr

[Chuck FB]

14 minutes ago, redwngr said:

2025 3500 battery/alternator ordering possibilities

 

 

 

 

Notes 1 and 2 on Alaskan Snowplow edition refer to WT  (1) and LT (2). Ut's not available on LTZ and HC 

 

 

 

Others are all trims, but have engine choice requirements

I would have to look at the Canadian Chev site but I don't recall ever seeing the Alaskan package, I've definitely heard of it though within the USA and looking at Alaskan dealerships that had them in stock as it probably is a popular option for some to get all the items needed for putting a plow on.

 

I'm not sure if you meant that a HC could not have dual batteries and alternators or probably me not understanding what you meant. Without a doubt my HC 3500 has what they call the KHF 220/170 alternators and the K4Z being the second battery. What I did not order it with but certainly could have and that was the snow plow prep which would have given me the 6000 lb torsion bars and the wiring extras that are behind the grill I believe as well as the harness that runs to the rear of the cab to power a strobe light etc.

 

What one can't get with a truck above an LT is a pto option, there must be something set up slightly different on the PTO offered transmission casting I would guess.

[redwngr]

I meant the Alaskan package is only available on WT and LT. 

 

Alaskan package (ANQ) is available on the US and CAN 2025 3500 order guides.  

 

There is also another snowplow package. 

 

 

Easier to read?

 

 

 

[redwngr]

As well as only available on WT and LT, PTO is also only available on duramax, and only with 4wd.

No available with adaptive cruise

 

[Chuck FB]

I stand corrected on the Alaska package ( I didn't even bother to look it up on the website now ) , perhaps it was the Texan package, something unique to the states that we didn't get here but a lot of these names they come up with are sort of gimmicks, like the trail boss name as well, just another packed trim level ( or the Z71 ! ) . 

 

Makes sense about the PTO, more of a diesel desired option anyway to run a hydraulic pump for a hoist or other attachment.

 

None of those things were on my want list and didn't look at the WT on the website, went through the motions of a gas LT and realized so many things were optional add ons vs standard or if even available at all. Just now looked at the stock the dealer I ordered the truck from has and a whole 4 gas trucks and the rest duramax. Also 6 2500's vs 30 3500's and that is typical of this area that they sell a lot more 3500's to the consumer market over the 2500. All reversed in the states with the 2500 over the 3500 because of licensing fees I gather.