1994 K3500 extended cab dually

[n8in8or]

Yeah, they're the same size pulleys. I'm not following how they could be fighting each other if they weren't spinning the same speed.....

 

[dbrannon79]

the higher RPM sometimes can allow one to push more amperage. something I was always told when running dual alts that each having their own built in regulators. iirc for them to work properly they would need diode isolators. I don't recall all the details though

 

[n8in8or]

the higher RPM sometimes can allow one to push more amperage. something I was always told when running dual alts that each having their own built in regulators. iirc for them to work properly they would need diode isolators. I don't recall all the details though

Hmmm..... I'm not sure that's rectifying in my brain (pun maybe intended), at least the amperage part. I doubt 2 production alternators on a dual alternator setup are capable of outputting the exact same amperage, not to mention if one fails and gets replaced with an aftermarket replacement. But more importantly, I think of amperage in this situation as being a pull, not a push, and it's just the alternators ability to feed that pull or not. If the alternator isn't big enough, then it can't satisfy the need all of the accessories in the truck are asking for and that's when you see lights dimming and such. So in my mind, the alternators are only putting out what is needed, and not forcing juice into the system beyond what is required, and so in that situation, I can't picture them fighting each other either as they would both be just sending their power into the cable.

I was going to say that I could maybe see a diode of some kind being needed, but then I believe that would counter my statement above about pull vs push, so I'm also thinking that isn't a thing. I was curious, so I just looked at the RockAuto catalog to see if it had listings for alternators in single or dual applications for a 1998 K3500, and it didn't say that. I also tried looking at a GM catalog for a 1998 K3500 and it only listed the alternators with 3 amperages, and not if it was single or dual alternator. I looked up both a 1998 and 2002 C3500HD to see if there was anything for single or dual alternators since it would be more common in that application, but unfortunately they don't even list the alternators at all for those.

I was able to grab the harness from the truck I removed the brackets from and I didn't see anything like a diode or anything in the harness - it was just a harness that plugged into the main harness and joined the plugs of the 2 alternators together. There didn't appear to be any more magic than that.

I could be wrong, and maybe I'll find I'm wrong when I go to wire these up and consult the wiring diagram in the factory service manual, but so far I don't see any evidence that makes me concerned about the alternators fighting each other in any way. I'll definitely report back if I do though.

 

[MrMarty51]

I do believe that there is some sort of a signal from the alternator on a single alternator system that triggers the tachometer into thinking its reading actual engine RPMs.
The pulleys from the 6.5 alternator has to be exchanged with a store bought alternator or else the tach will read faster.
I dont know what that signal is called but I do know its in relation to the alternator.
If two alternators are running in parallel, IDK if it would be possible to get both alternators to form that wave in unison or if one would happen to form the wave offset so it would appear to the ECM as just one flat plane with no signal IDK.
I think thats what Doug was referring too in his last post and why it may be possible that a diode may be needed to isolate the one alternator from the other to avoid mixed signals.
I think maybe in order to get an accurate picture of what alternators was used on the dual alternator systems might be to go to the GM dealer and have them look up the dual alternator system for an ambulance application then maybe if there would be a difference the parts book should show.
If the GM parts department can even go back that far.
The dealer here can look up parts for my 2000 year truck and give me a part nummer but then it lists the parts as NLA.

 

[n8in8or]

I do believe that there is some sort of a signal from the alternator on a single alternator system that triggers the tachometer into thinking its reading actual engine RPMs.
The pulleys from the 6.5 alternator has to be exchanged with a store bought alternator or else the tach will read faster.
I dont know what that signal is called but I do know its in relation to the alternator.
If two alternators are running in parallel, IDK if it would be possible to get both alternators to form that wave in unison or if one would happen to form the wave offset so it would appear to the ECM as just one flat plane with no signal IDK.
I think thats what Doug was referring too in his last post and why it may be possible that a diode may be needed to isolate the one alternator from the other to avoid mixed signals.
I think maybe in order to get an accurate picture of what alternators was used on the dual alternator systems might be to go to the GM dealer and have them look up the dual alternator system for an ambulance application then maybe if there would be a difference the parts book should show.
If the GM parts department can even go back that far.
The dealer here can look up parts for my 2000 year truck and give me a part nummer but then it lists the parts as NLA.

Yes, diesel trucks use the alternator to run the tach, so you have to have the correct pulley on the alternator so the RPMs run correctly. I bought the correct pulleys for the alternators. I could have only bought the correct pulley for the main alternator, but chose to get it for both alternators just so they matched. You only need to run the tach signal from one alternator, not both. These are the pulleys I bought:

Pulley Alternator For Delco S6 10-12-15-17Si Cs130-144 62Mm Od 24-1250 | eBay

PULLEY CLASS S6. Delco 10474364, 10498550, 1979746, 1989104. TYPE Pulley. SAVE UP TO 5%. SHAFT DIA 17.

www.ebay.com

I took the harness from the truck I got the dual alternator setup from. I don't have it in front of me, but as I recall, it had just one wire that jumped over to the second alternator, which I'm assuming was just the signal to energize that alternator, but I haven't gotten to the point of doing actual wiring yet.

 

[dbrannon79]

I believe it's the L terminal on the alternator pigtail but don't quote me on that! the tach reads RPM from the pulses on the field winding as the alternator spins. having both wired as 1 would effectively send a doubled pulse signal to the tach. I would take an ohm meter and probe the terminals on both and make sure they are not tied together into one signal wire. that would send mixed signal to the tach both alternators can work together just fine being tied together otherwise, it's just you wouldn't want the signal to the tach reading coming from both at the same time. that is where the diode comes into play. if you find they are tied together, you will want to separate the signal going into the cluster but keep it together going into the ECM.

 

[n8in8or]

It's the P terminal on the alternator that runs the tach. I'll only be running the tach off of one alternator, not both, so I won't be crossing the streams like in Ghostbusters.