M925A2 Delco Style Alternator

tractors0130

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I just finished installing a 21SI Delco style single wire 70amp alternator on my M925A2 with the 8.3L Cummins and single belt after the original 60 amp Leece Neville fried. Install was pretty easy, just had to put a slight notch in the upper factory bracket with a short spacer and lengthen the lower brace by 1.75" to use the original belt. The original style alternator could always be put back if someone wanted to. I need to put a little longer bolt in the rear upper alt. mount to brace the heater hose, paint the bracket and spacer and put some rubber guards around the rear alt. connections to protect them. As seen in the pics. it's charging at 28.2 volts with 14.1 volts on the "R" terminal. Instructions say not to exceed 4 amps on the "R" (relay) terminal.
 

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tractors0130

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The 21SI alternator was from Spidermarine, link below. I also purchased the 8 groove serpentine pulley from them, it was not listed on their website. I had give them a WAI pulley part # and they crossed it over to their number of 208-12003 (sku # 113377). Pictures are the 2 different WAI pulleys, part # 241752 for the 3.43" pulley and part # 241753 for the 2.76" pulley. Price total was $150 for alt. ($109.99), pulley ($20) and shipping ($20). You could probably use the lower voltage terminal on the back as long as there was an inline 4 amp fuse and a disconnect to turn it off when not in use.

http://spidermarine.com/showitem.aspx?&id=104834&name=100%25%20NEW%20Delco%20%2024%20Volt%2070%20Amp%2021si%20Alternator
 

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BKubu

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I was just going to ask what it cost! Thanks for the info. A new 60 amp alternator runs around $300 (I just bought one NIB). So, this conversion saves you about half, slightly less when you factor your time in. Good deal! I have a bunch of either new or rebuilt alternators that WILL NOT put out the correct voltage no matter the many times I have tried to adjust them...even had others try, too, but to no avail. I was thinking of getting them rebuilt...but this is probably the better route.
 

CPDOG

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hello from Seattle,

I know you posted this a while ago, but I own an m923a2 and was wondering how the alternator set up is still working for you?
I called spidermarine today and they said they didn't know how it was producing 12 volts from terminal "r".
but the guy I spoke to was pretty **** rude and seemed he just didn't want to deal with anybody, so if you have any input please reply and let me know.

lastly, did you hook up the 12 volt to any other items such as using it to charge a stand alone battery?

V/r
Columbus Partin
 

tractors0130

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The alternator worked fine with no issues for about a year and half, then I sold the truck. I never hooked anything up to the "R" terminal, originally I had planned to wire it to a cigarette lighter socket to charge phones or GPS usage. Spider Marine was very good to deal with when I had bought the alternator and pulley.
 

QB144K

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Hello seattle from lake stevens WA

I have a 1983 M923a2 and I did he Delco 21Si conversion about 8 months ago and have had know problems with it at all. I have my original alternator still but I will never put it back on.
 

74M35A2

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The "R" terminal on heavy duty alternators is typically a single phase sine wave (AC voltage) output. Historically used for a diesel tachometer, or to trigger an hour meter to run (so key left on does not rack up hours). It is not designed for any type of loading. Check the terminal with your meter on AC just for kicks with it running, and you may likely see 28.2V (which half of that wave would be the 14.1V you are seeing). Again, it is only half of an AC wave, it is not a linear DC output. Best to not utilize it for anything.

Tractors - I love my M925A2 I purchased from you! Put 4000 miles on it so far in the year since acquiring it from ya. I'd recommend you to anybody looking to buy an MV.
 

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155mm

Chief and Indian
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Why would you not use the 'R' terminal to connect the butt connected wire from the old alt? It uses AC volts. I think the wire #is 599 or 566, that wire goes to the PCB and tells the PCB that the truck is running and it will function properly. What do you do with the other small wire, i dont know the number on it? Just tie it back and insulate it? It should be a hot wire also going to the PCB.
 
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manders

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So you don't hook up either small wire? Just cap them off?
I installed this same alternator, but I've been really remiss in not doing a write-up.

I connected just the two main wires, with nothing on the other two "small" terminals.

It's been working great for about 10 months. (Mine is not a daily driver, so those 10 months are maybe 200 miles.)

HTH

FinalConnections.jpg
 

dawico

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I installed this same alternator, but I've been really remiss in not doing a write-up.

I connected just the two main wires, with nothing on the other two "small" terminals.

It's been working great for about 10 months. (Mine is not a daily driver, so those 10 months are maybe 200 miles.)

HTH

View attachment 551488
Thank you. Tackling mine tomorrow and just wanted to be sure I understood correctly.
 

PaFarmer

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This was a timely update. I just received a 21SI delco alternator. My terminals are a bit different than the one originally posted. I have four terminals. A small post R, a large post BAT, a small post 1 and a large post GRD. I just need to hook up the battery cable and the ground and cap off the other wires when I remove the existing alternator? Seems easy enough.
 

tractors0130

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This was a timely update. I just received a 21SI delco alternator. My terminals are a bit different than the one originally posted. I have four terminals. A small post R, a large post BAT, a small post 1 and a large post GRD. I just need to hook up the battery cable and the ground and cap off the other wires when I remove the existing alternator? Seems easy enough.
That's all you need to do as long as it is a single wire self energizing alternator, just disco your batteries before working on the alternator to avoid shorting anything or you out.
 

dawico

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That's all you need to do as long as it is a single wire self energizing alternator, just disco your batteries before working on the alternator to avoid shorting anything or you out.
If I have read properly, you may want to charge up your batteries before trying it too. It is hard for an alternator to charge up dead batteries.

That is my plan.

Hopefully you have a new pulley also. The original will not fit on the Delco.
 

74M35A2

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If there is enough energy in the batteries to start the engine, then the alternator should charge them just fine. Even with dead batteries, an alternator should charge them without suicide. That is 50% of its job description after all. The factory unit may not exactly be up for this from the stories I hear. The Delco and Delco clones should be fine with it.

If you are worried about toasting an alternator while charging batteries, increase the engine rpm above idle so the voltage regulator can have some off time (produced current greater that that requested by the batteries), and also the cooling airflow though the alternator will be much higher. Both of these factors separately and especially combined will allow the electronics to run cooler and lower their risk of failure.
 

CPDOG

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all

I have just burned up my second military 60 amp alternator.
I am ordering my new 21si tomorrow , so just for my clarification of the above posts, the 2 small wires don't need to be hooked up? only the pos and neg need hooked up.
if I am incorrect here, any and all input would be greatly appreciated.

V/r
 
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