Alternator/Tach questions

[RyanB]

Hey all. Been working on my conversion for oh... (2 years today actually... Ground Hog day 2004) and things are starting to come together rather fast. Actually the engine is just going to get built with all the good stuf right now at a well known Indiana shop as I speak/write. Anyway, now is time to get the little things figured out. What is everyone doing for there alternator in the 88-98 Chev conversions. I am wanting to keep everything look as stock as possible without making special brackets or anything! I am wanting to run the Dodge Alternator but relize I might have some problems. My truck was a 6. 5L and had the tach pickup in the alternator. Would it be at all possible to hook the tach up to the crank sensor like the dodges have? Also, will the dodge alternator even charge or will I have to have someone modify the internals? The AC compressor is mounted at the stock location on the cummins and I have notched the frame for it. Just have to figure out these little things now!



Thanks in advance... Ryan

 

[autoworld]

you need to build or have us build you an alt bracket due to the fact that the tach sensor is in that alternator on that ex 6. 2 -its too late now but notching the frame is

not the best thing to do, it compromises the strength. we always bracket and relocate the stock a/c. it also saves dealing with the hoses, dryer, etc. -i can give you more details on how that is all acomplished if you wish - can send you a few pix of the one that just went home.

dawna

 

[RyanB]

Sure, how about you just post them on here for all to see! Actually the way I notched the frame actually increased the strength... you should see it! I no longer needed the IFS steering anyway (swapped in a dodge 60 with 05 Ford trailing arms/springs). Anyway, like I said I would rather just try to figure out a way to use the dodge alt... . I have heard it been done in the past, just have to figure out how. The wiringing harness I have is actually a 1999 6. 5 unit as well as the dash and the whole unit. Do you know or does anyone know if I can use the crank senser for the tack on my truck? not sure if this is possible or not but sure would like to figure out how to make that work. I remember seeing a post on the 1st gen board a while back where they modified the stock Alt for a tach... actually that may be in one the past issues. I will have to look for that tonight yet.



Here is a question- What is the difference in the actual charging system on the cummins/dodge to the 6. 5/GMC ?



Thanks... Ryan

 

[LNeshem]

Hey ryan, just got my alternator charging today! I used a external regulator for an 85 dodge. It was 11. 99 at autozone. The terminals aren't marked but thanks to PKirby I learned that you hook up a wire that is hot with key on to the middle terminal on the regulator and also run a wire from that terminal to 1 of the small terminals on the alternator. then run 1 more wire from the remaining terminal on the regulator to the other small terminal on the aqlternator and it is charging great. When you first look at the regulator it is kinda wierd cause the plug looks like it has 3 terminals but 1 is a blank and that is how you get a middle terminal. Lowell

 

[autoworld]

charging system/alternators:

the ford and chevrolet alternators are "internally" regulated, the GM tach signal is in the alternator, if the tach signal is too slow (check with an external guage), the alternator pulley can be changed to speed it up. on the 97 chev pictured below, it came with a 6. 5 diesel-our tach signal was 450 rpms slow. we machined a smaller pulley for the alternator and changed it out brought it back to close to correct - charging great. regulators went out in the early 70's in GM.

the dodge alternator is "externally" regulated, by the dodge computer. if the control is not there by the dodge computer, it won't charge correctly, if it doesn't shut off and

continues to charge, it will boil the battery, let alone what spikes can do to the engine and power train computers.

these pictures are of a 97 chev with a 97 cummins. - hopes this explains things a little better. i probably have some better pictures in being developed.

dawna

 

[RyanB]

Unfortunatly I couldn't put the AC up on top like thos pictures. I had the engine sitting just a little to high when I finaly figured out. Anyway, I remembered seeing a picture of someone taking apart a dodge ALT to wire in a tack wire... couldn't remember which TDR magazine it was in so I started at my olded issue (I have about 25 now!) well if it wasn't the latest issue!!!!!! oh well, some good reading anyway! It is the new one with the Red Mega Cab on the front in the 1st gen section. Wonder if that would work on the 2nd gen ALT??? I would then do the external regulator thing for it to work right.



Good job on those conversion pictures though!!!

 

[autoworld]

we usually dont put the AC up top, that particular application came that way, so we did what was best for this truck - we'd have had to buy parts and relocate the whole system. making things "work" when it comes to electrical regulation is not advisable

because of the damage to the computers with any kind of spikes, they are very expensive to replace vs doing the stock alternator, externally regulating an internally regulated alternator i would suspect would cause conflicts also. this forum is great but advise from someone who has made something "work" may not be the right thing and

i'm sure when things go wrong after time they don't come and tell you "oops" it fried my computer and gees that thing costs $700. 00... i know i'm just a girl, fellas. . but i have been here thru every single one of the 205 conversions. we have made all the mistakes, cost time and money correcting them and have the best out there in Doug

who is an electronics whiz to help us thru the difficult issues like the 2005 systems,

i'm just trying to save you some major headaches!!!

dawna

 

[RyanB]

Okay, I am starting to see what you mean now by keeping the stock GM ALT. Is it possible to get a close up of the ALT on your trucks? just want to see how close to stock this looks and if I am out to lunch on this. Also, I take it its not as simple as a pulley swap from dodge to GM? are there any other applications of pulleys in 8 rib that would work. I work for a trucking company and have access to pretty well any part I want! Even another alternator that would work... Reminds me... my boss owns two little T300 Kenworths with 8. 3L cummins in them. I wonder what they have for an alternator... will have to look into that and I am sure the bracketry is all the same as there little brother. I know they have the AC up on top where yours is located... just wonder now about the ALT.

 

[autoworld]

shoot me your regular email address and i will send you some pictures out tonite where you can see these things before the radiator is in, they are pretty tucked in there when complete (after i get home from pool leagues )

dawna

 

[DKarvwnaris]

Reminds me... my boss owns two little T300 Kenworths with 8. 3L cummins in them. I wonder what they have for an alternator... will have to look into that and I am sure the bracketry is all the same as there little brother. I know they have the AC up on top where yours is located... just wonder now about the ALT.

The alternators on the GM light duty trucks are completely different from the medium duty and heavier trucks. The tach pickup on the cummins in the larger trucks works off a cam or crank sensor, not the alternator.

Your best bet is to just utilize the factory tachn signal in the alternator. If you don't have the skills to fabricate the brackets to look as if they were factory installed, I reallyu recommend you take Dawna up on her suggestion to sell you a GM alternator bracket like they build for theirs. I have reservations of recommending Dawna to post very vivid pics of their mounts since the internet is full of lookie loo's who only want examples of someone else's hard work to copy themselves (not saying you are, but too many else have done this in the past. Since its their business, and not a hobby, I think they have a right to ask for compensation for their craftsmanship. If you buy one and then copy it, you at least give them one order for it, thats what fordcummins.com did to them )

To change the pulley size on the GM alternator, you just need to figure the actual RPM of the engine and then adjust the pulley size ratio. A few of the pulley's on the lighter MDT's such as the 6500 series GM topicks are the same shaft diameter as the pickup alternators. You just need to measure the Harmonic balancer pulley of the Cummins and then compare the harmonic pulley on the original GM 6. 2 or 6. 5 to get a rough idea what size you'll need to step the Alternator pulley up or down to. The only thing remaining a constant is the alternator's rpm's, which is a good thing since you will end up in the correct alternator speed to make it charge properly as well.

 

[PKirby]

I fully agree with Dawna about using the vehicle's original alternator on late model computer controlled conversions. This is especially true on the latest CAN Com controlled vehicles that have several computers that communicate with each other through the CAN circuit.

I work in the Lab at an auto manufacturing plant and regularly work on engine control circuits and they are very sensitive to modifications.



On an older, non computer controlled conversion, I think the 2 terminal regulator and Dodge alternator is a good setup.

 

[RyanB]

That does make alot of sense. I would think though that seeing this is a 88-98 with a 12valve cummins going in. 6-speed manual... that there wouldn't be any computer needed other than for the speedo and cruise if I even go with cruise! I think the 2 terminal regulator might be the best thing for me... now all I have to do is figure out the tach!



Ryan

 

[DKarvwnaris]

That does make alot of sense. I would think though that seeing this is a 88-98 with a 12valve cummins going in. 6-speed manual... that there wouldn't be any computer needed other than for the speedo and cruise if I even go with cruise! I think the 2 terminal regulator might be the best thing for me... now all I have to do is figure out the tach!



Ryan

You have listed several different year GM trucks in this thread, so I am getting confused as to which you are actually using. If you have a 95 or newer GM cab, the climate controls are electronic on the dash. They are controlled by a secondary electronic controller box. (much like the 2nd generation dodges were).

If you don't want electronics in the engine compartment, I understand, but you need to make sure there is nothing in the cabs secondary systems that use them as well. Surge spikes and uneven power from the charging system will cause trouble to any circuit board it is feeding power to. The GM alternator is the easiest solution for you, but if you want to complicate it, go for it, your choice, your truck, your parts.

 

[RyanB]

Your right on the 95-up cab... well, dash anyway! I got the wrecked cab and everything worked incliding all the heater functions and radio controls. The only computer I got was the one in the cab behind the glove box. Also the speed buffer sensor and the whole speedo is controled by that computer. We will see what happens and currently I am looking for a 8 rib pulley that bolts to the GM Alt.

 

[DKarvwnaris]

Your right on the 95-up cab... well, dash anyway! I got the wrecked cab and everything worked incliding all the heater functions and radio controls. The only computer I got was the one in the cab behind the glove box. Also the speed buffer sensor and the whole speedo is controled by that computer. We will see what happens and currently I am looking for a 8 rib pulley that bolts to the GM Alt.

You can run a 5 rib belt to get the truck running. This will solve the 5 rib to 8 rib alternator pulley search until you stumble across one. This will also open up several options for you to search out different diameter 5 rib pulleys in case the tach is not calibrated correctly due to the Cummins harmonic pulley being different from the the GM Crank pulley. Once you have the RPM reading correct by trying different pulley diameters, you can then take the pulley to a machine shop and have it custom turned to insure the deck height is also compatible with your existing belt path and alternator mounts. I know of several guys running the 5 rib belts lpermanently to resolve this issue. The p-30 chassis GM vans had 8 rib pulleys on their alternators, My 4bt even has the 8 rib pulley on the alternator. These are easily referenced off of a VIN # or a medium duty GM truck dealer. Few p-30 chassis alternators will have this pulley on them, you usually have to swap it with the original one when yuo buy a recon'ed one.

 

[RyanB]

DKarvanvaris- Thanks for the great imput. I have been doing some searching to find out the pulley size needed and from what I see is it goes by a ratio. There for what I have to figure out is the ALT pulley ratio on the 6. 5L (what my tach is set up at now) and then take the crank pulley size of the cummins and work back words with the ratio I need it to equal there for letting me know the ALT pulley size I need... . Does that sound at all right? I think I confused my self! So the main thing that I need to figure out is what size crank pulley the 6. 5 has versus the cummins. If they are the same size nothing has to be changed. If the Cummins has a larger pulley there for the alot would then need a smaller or larger pulley also???



Hopefully I didn't confuse everyone!



Ryan

 

[DKarvwnaris]

DKarvanvaris- Thanks for the great imput. I have been doing some searching to find out the pulley size needed and from what I see is it goes by a ratio. There for what I have to figure out is the ALT pulley ratio on the 6. 5L (what my tach is set up at now) and then take the crank pulley size of the cummins and work back words with the ratio I need it to equal there for letting me know the ALT pulley size I need... . Does that sound at all right? I think I confused my self! So the main thing that I need to figure out is what size crank pulley the 6. 5 has versus the cummins. If they are the same size nothing has to be changed. If the Cummins has a larger pulley there for the alot would then need a smaller or larger pulley also???



Hopefully I didn't confuse everyone!



Ryan

Seems your "research" is not very good?. .

If the pulley on the 5. 9 is larger, you need to increase the alternator pulley to balance the RPM ratio, not decrease it. Simple math

Don't overthink this, its not worth the effort. If you can't visualize this correctly, take a look at a 18 speed bicycle's gears and derailer set up, same principle. The more you try to think this out instead of just starting the truck up and checking the RPM's, the more you're going to be upset when you still don't have it right.

If you're looking for a reliable and easy way to get the ratio right, do as I said with the 5 grove belt and different pulleys from a junkyard. Several small GM unibody car alternators will match shaft pulley size.

If you end up deciding to have a pulley built at a machine shop, take them the four pulleys from the two engines and tell them to match ratio with the GM and Dodge setup. If they have CNC programs, it is just a few keystrokes for them to find it dead on for you, no guess work.

 

[duallyguy95]

any picture or diagram on how i can wide cummins alt with external voltage regulator to 1995 chevy 3500 with no problems

charging system/alternators:

the ford and chevrolet alternators are "internally" regulated, the GM tach signal is in the alternator, if the tach signal is too slow (check with an external guage), the alternator pulley can be changed to speed it up. on the 97 chev pictured below, it came with a 6. 5 diesel-our tach signal was 450 rpms slow. we machined a smaller pulley for the alternator and changed it out brought it back to close to correct - charging great. regulators went out in the early 70's in GM.

the dodge alternator is "externally" regulated, by the dodge computer. if the control is not there by the dodge computer, it won't charge correctly, if it doesn't shut off and

continues to charge, it will boil the battery, let alone what spikes can do to the engine and power train computers.

these pictures are of a 97 chev with a 97 cummins. - hopes this explains things a little better. i probably have some better pictures in being developed.

dawna