M925A2 Delco Style Alternator

simp5782

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Hello,
New to the site, this being my first post. I am running into the same problems as everyone else on this thread with the generator not charging the batteries properly. I have decided to convert to the 21SI alternator and by reading through this thread I have determined I will need a new 7/8" shaft V belt pulley to go in this new alternator. I see there is a new bottom bracket that comes from Cummins that bolts on the bottom for the 6 CTA 8.3 engines. However, I have an NHC-250 engine. Does this still require the bottom bracket or will the new alternator bolt right on? After reading the thread I am still confused about this.
Thanks!
For the 33si on an NHC250

For a 24si alternator on an NHC250

I have the new delco 100amp 33si alternators for sale if interested
 

74M35A2

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Thanks guys.

I only know how to get spot-on alignment with the 8.3L since that is all I own. Most all 250 engine owners have each done something slightly different from one another, regarding pulleys, brackets, spacers, bolts, and tensioner. The configs are slightly different, as the 8.3L main support bracket is the upper one, and I believe on the 250 the lower bracket is main support. 8.3L has a spring loaded serpentine belt tensioner, 250 uses alternator pivot for belt tensioning.
 

74M35A2

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For the 250, the latest craze is to slot the 3 holes of the stock bracket on a mill. This allows you to align it easily. Still does not support it properly, but seems to work for most.

I always intended to find a bracket for that engine as well, but never did. It was usually done by the truck makers and not Cummins, so a pinch harder but not impossible. Really just need to find that engine block as used in a non military application and it will have the civilian spacing between the ears vs the euro/military spacing. Then find out who sourced it, Cummins or vehicle/equipment maker.

I think most people want the right bracket. Nearly 100% of the 8.3 kits I sold, they all wanted the right bracket for proper support vs a long bolt with spacer tube, even though it is a $100 Cummins part.
 

Corn

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I am in need of a little more advice. I hate to admit what I have done, but if it's the worst that ever happens to me I'll be ok. I gathered the supplies that I needed for the alternator conversion, had a local shop build a genuine delco 21 SI 24V alternator for me and I put it on. It was getting dark and I should have waited but weather was moving in for the next few days. In rushing it I got my positive and negative crossed on my alternator. I turned the battery switch on but did not start the truck. In about 10 seconds the wires running into the engine control box on the firewall started smoking and I turned the battery switch off as fast as I could. I figured that had done it and I had fried who knows what but I swapped the cables on the alternator and the truck fired up after that with no problems. I checked everything (lights, transmission selector, charging system etc.) and it was all in working order. The alternator was reading 27.7 out the back with a voltmeter. The next day I took it for a test drive and 3 miles in the alternator started smoking and melted a small part of the housing on the back of the alternator. My question is have I done internal damage to the ECB or is there some kind of regulator on the alternator I could have knocked out? I hesitate to put another alternator in fear the same thing will happen. I highly doubt it was just a faulty alternator after the stunt I pulled. Any advice would be appreciated. Thanks.
 

74M35A2

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I am in need of a little more advice. I hate to admit what I have done, but if it's the worst that ever happens to me I'll be ok. I gathered the supplies that I needed for the alternator conversion, had a local shop build a genuine delco 21 SI 24V alternator for me and I put it on. It was getting dark and I should have waited but weather was moving in for the next few days. In rushing it I got my positive and negative crossed on my alternator. I turned the battery switch on but did not start the truck. In about 10 seconds the wires running into the engine control box on the firewall started smoking and I turned the battery switch off as fast as I could. I figured that had done it and I had fried who knows what but I swapped the cables on the alternator and the truck fired up after that with no problems. I checked everything (lights, transmission selector, charging system etc.) and it was all in working order. The alternator was reading 27.7 out the back with a voltmeter. The next day I took it for a test drive and 3 miles in the alternator started smoking and melted a small part of the housing on the back of the alternator. My question is have I done internal damage to the ECB or is there some kind of regulator on the alternator I could have knocked out? I hesitate to put another alternator in fear the same thing will happen. I highly doubt it was just a faulty alternator after the stunt I pulled. Any advice would be appreciated. Thanks.
If the alternator got hot enough to melt aluminum, then there is a dead short in it somewhere. Likely the diode bridge in the back, but at those temps it can melt the varnish off the copper wires of the stator as well. Best and safest thing to do is yank the pulley and ditch the rest of it for another one. The alternator is powered all the time, you don’t need it bursting into flames in the middle of the night in an effort to save $300.

Regarding the PCB, it is designed to protect against reversed battery connection. Not sure how it will act with just reverse alternator connection, but it probably viewed it more as a short than reverse. If the truck still cranks, runs, and shuts down correctly, and the dash power still works on/off properly, then the PCB should be OK. It is really just 2 solenoids inside it. One for dash power, one for starter solenoid.

Melted wires won’t be reliable, they will quickly corrode under the insulation. Need to replace them to keep it reliable as well.

In all, not a big deal, truck did not burn down. I dead shorted my starter lead to the block by dropping a ratchet and almost burned the truck down. Had to replace some wiring but all OK after.
 

Corn

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If the alternator got hot enough to melt aluminum, then there is a dead short in it somewhere. Likely the diode bridge in the back, but at those temps it can melt the varnish off the copper wires of the stator as well. Best and safest thing to do is yank the pulley and ditch the rest of it for another one. The alternator is powered all the time, you don’t need it bursting into flames in the middle of the night in an effort to save $300.

Regarding the PCB, it is designed to protect against reversed battery connection. Not sure how it will act with just reverse alternator connection, but it probably viewed it more as a short than reverse. If the truck still cranks, runs, and shuts down correctly, and the dash power still works on/off properly, then the PCB should be OK. It is really just 2 solenoids inside it. One for dash power, one for starter solenoid.

Melted wires won’t be reliable, they will quickly corrode under the insulation. Need to replace them to keep it reliable as well.

In all, not a big deal, truck did not burn down. I dead shorted my starter lead to the block by dropping a ratchet and almost burned the truck down. Had to replace some wiring but all OK after.
Thank you for the advice!
 

CARMAN

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Bumping this cause I just reread it. Last time was a couple years ago. Great wealth of info!! My parts are on the way! Thank you 74M35A2 for the tech talk.
 

74M35A2

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Mixed opinions. The larger alternators do fit and work, but do not charge at idle.

I would say it depends more on your intended usage of the inverter. What is its rated (not peak) watts, and how many watts do you intends to use, and for how long? Also, when would you be using those watts, driving? Engine idle? Engine off? Truck stopped by engine speed increased via cable throttle?

Let me know more, we can try to get you best configured. I do have the larger alternators here as well, but basically quit selling them because people complain that their volt gauge is in the yellow at idle.
 

simp5782

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Mixed opinions. The larger alternators do fit and work, but do not charge at idle.

I would say it depends more on your intended usage of the inverter. What is its rated (not peak) watts, and how many watts do you intends to use, and for how long? Also, when would you be using those watts, driving? Engine idle? Engine off? Truck stopped by engine speed increased via cable throttle?

Let me know more, we can try to get you best configured. I do have the larger alternators here as well, but basically quit selling them because people complain that their volt gauge is in the yellow at idle.
Pretty sure the remote sense alternators charge at idle
 

74M35A2

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Pretty sure the remote sense alternators charge at idle
Not if they are brushless, which most are. The brushless ones have very low idle output.

Up to you, I have one here if you want, but I think you are better with the one you just received. People tend to get hung up on the total output number, rather than output at idle, and then they get mad their gauge is in the yellow unless they rev the engine up.

We can switch them out if you want to send me the one you just received, and $40 to ship this one to you. They are heavy. They look cool, and do make a lot of power, but not at idle. You will have a voltmeter in the yellow at idle, and probably even the red if using your inverter heavily at idle.
 

Steelreaper80

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Mixed opinions. The larger alternators do fit and work, but do not charge at idle.

I would say it depends more on your intended usage of the inverter. What is its rated (not peak) watts, and how many watts do you intends to use, and for how long? Also, when would you be using those watts, driving? Engine idle? Engine off? Truck stopped by engine speed increased via cable throttle?

Let me know more, we can try to get you best configured. I do have the larger alternators here as well, but basically quit selling them because people complain that their volt gauge is in the yellow at idle.
It would be used mostly at idle but throttled up to a higher idle via hand cable. 2000 watt inverter running a small 1500 watt space heater over night that runs off and on. I sleep in my truck when I am in the field working and it gets cold in the dead of winter. Heater won't be running full tilt all night, just occasionally to keep me from freezing my begonias off. New truck heater core and blower but at idle, the truck sometimes blows cold air even though it is running.
 

porkysplace

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It would be used mostly at idle but throttled up to a higher idle via hand cable. 2000 watt inverter running a small 1500 watt space heater over night that runs off and on. I sleep in my truck when I am in the field working and it gets cold in the dead of winter. Heater won't be running full tilt all night, just occasionally to keep me from freezing my begonias off. New truck heater core and blower but at idle, the truck sometimes blows cold air even though it is running.
Do you have a winter front for the radiator ?
 

Steelreaper80

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Mixed opinions. The larger alternators do fit and work, but do not charge at idle.

I would say it depends more on your intended usage of the inverter. What is its rated (not peak) watts, and how many watts do you intends to use, and for how long? Also, when would you be using those watts, driving? Engine idle? Engine off? Truck stopped by engine speed increased via cable throttle?

Let me know more, we can try to get you best configured. I do have the larger alternators here as well, but basically quit selling them because people complain that their volt gauge is in the yellow at idle.
So I ran a test on my little heater. I throttled the engine with the hand throttle up a tad to high idle. I set the thermostat on the heater to a comfortable level. It would cycle on for about 2-3 mins then cycle off. It is small but really cranks out the HEAT! During the on cycle, it would pull the voltmeter down to the middle of the yellow. As the heating element turned off but the blower motor stayed on it would go back to the middle of the green. My question is, would this drain the batteries? It would stay off about the same time as it was on and honestly, I needed to turn the thermostat on the heater down to stay off longer. It got really hot in the cab quickly. Nice little heater.

Another question-as long as the alternator is 24 volts and has a J-180 mount, and a single point connection for the negative and positive wires, it should work, correct? I have the correct pulley on my existing 21SI clone so I don't need a pulley.

I found this on Amazon. 24 volt, J-180 mount, and single-point connection. 140 Amp.

 

simp5782

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What is the battery voltage when the element turns on and off? Don't trust that gauge since it's working off of dash power which can be nearly a volt off from battery volt.

Any 180 long will work . Since you have to rely on your truck I would use a name brand alternator
 
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