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Delco 10SI alternator help needed

Z

Zachary Hoyt

Well-known Member
I have a Farmall H that I need to redo the electrical system on. It was converted to 12V by a previous owner and set up with a Delco 10SI alternator. A few months after I got it the alt quit so I replaced it. The new one lasted a few more months and then also quit. I need to rewire the tractor and will follow the wiring diagram on the Farmall forum, but I am wondering if I need a new alternator or if there is some sort of VR or fuse or other thing in or on the 10SI that I could replace that would be cheaper and make it work again. I do not know anything about alternators, I just hooked the new one up the same way the old one was. When I pulled the knob that connected the alt to the battery after startup it originally would show a charge, but then one day it started showing a 5 or 10 amp discharge when I pulled the knob, so I pushed it in again and left it that way for the past few months. The tractor has a mag so it has been running without a need for the alternator. Any help will be much appreciated.
Zach
 
An alternator consists of four main systems.
all of them easy to work on. Good old bearings to hold it together, A regulator to feed voltage to the rotor through brushes, and a diode pack to convert alternating current into direct, lastly it has a stator, (windings around the outside) and a rotor that is a NSNSNSNS magnet on the inside. Replacing the regulator is easy. replacing the brushes is easy, replacing the diode pack is easy. SOme soldering is needed, but it is no nightmare. Jim
 
The 10SI and 12SI is probably one of the easiest alternators to repair. No desoldering and no press-fit bearing in the back. Most common things to check or replace are the field brushes, the diode trio, and the regulator. All cheap. It's a 15 minute job to pull one apart and replace all I mentioned. Brushes come out the back without taking it apart at all. Regulator and diode trio are inside. Diode trio is easy to check with an ohm-meter.

10SI also has a regulator test/bypass port in the back. When running, you stick a small nail in the hole and see if it starts charging. If it does, it means the alternator is fine but the regulator is bad. That is why the test port is there. To ID a bad regulator. New reguator costs around $15.
 
Here are what the parts look like . .

Diode trio -this is the set of diodes that usually fail and they bolt in - no soldering

<a href="http://s104.photobucket.com/albums/m162/jdemaris/?action=view&amp;current=Delcodiodetrio.jpg" target="_blank">
Delcodiodetrio.jpg" border="0" alt="Photobucket
</a>

This is the 3-wire regulator . .

<a href="http://s104.photobucket.com/albums/m162/jdemaris/?action=view&amp;current=Delcodvioltagereg3wire.jpg" target="_blank">
Delcodvioltagereg3wire.jpg" border="0" alt="Photobucket
</a>

this is the 1 wire regulator (self excite) . .

<a href="http://s104.photobucket.com/albums/m162/jdemaris/?action=view&amp;current=Delcod1wirereg.jpg" target="_blank">
Delcod1wirereg.jpg" border="0" alt="Photobucket
</a>

This is the brush and holder assembly that comes out the back. Brushes are kept in place with a toothpick that you pull out once installed . .

<a href="http://s104.photobucket.com/albums/m162/jdemaris/?action=view&amp;current=Delcodbrushholder.jpg" target="_blank">
Delcodbrushholder.jpg" border="0" alt="Photobucket
</a>
 
Last fall my buddy Wilson and I helped out at the local vocational ag school and its amazing how simple those Delco Alternators are to work on. He and I were showing the students the basics of generators and alternators and I had hardly turned my back and Wilson had the alternator apart showing them how easy it was to replace the small carbon brushes and the diodes and/or regulator if needed. Im not sure but NAPA or a good genny/alternator/starter shop may have the parts on the shelf so Id give it a shot if I were you at repairing it. Of course, first make sure its wired right.

John T
 
You have something mixed up. The brush assembly is held in with the same screws as the regulator. Mopar brushes can be changed from the outside.
 
Yes, I wrote fast and did not explain correctly. Brush holder comes out the back half of the 10SI alternator -once split. Alternators like the OEM Motorolas used OEM on many tractors are the ones that have completely externally accessed brush-holders.
 
Delco SI series are the only alternators I know of with "quick test" hole in the back. You should aways use that port and test first if it doesn't charge. Just stick a nail or equiv. into the hole and make sure it's shorted agasint the alternator case. It bypasses the regulator and "full fields."

<a href="http://s104.photobucket.com/albums/m162/jdemaris/?action=view&amp;current=Delcotesthole.jpg" target="_blank">
Delcotesthole.jpg" border="0" alt="Photobucket
</a>

<a href="http://s104.photobucket.com/albums/m162/jdemaris/?action=view&amp;current=Delco10SItesthole2.jpg" target="_blank">
Delco10SItesthole2.jpg" border="0" alt="Photobucket
</a>

<a href="http://s104.photobucket.com/albums/m162/jdemaris/?action=view&amp;current=Delco10SIpartsbreakdown.jpg" target="_blank">
Delco10SIpartsbreakdown.jpg" border="0" alt="Photobucket
</a>
 
I am wondering about two of your statements:

"A few months after I got it the alt quit so I replaced it. The new one lasted a few more months and then also quit."

"When I pulled the knob that connected the alt to the battery after startup..."

What is this switch? Is it a switch in the #1 wire to the alternator to energize it to begin charging or is it a disconnect switch that you turn off when the tractor is not in use, then turn it on when the tractor is running and you want to charge the battery.

Your description sounds like it may be the latter.

An alternator needs the battery load when running. I'm wondering if a no load at startup and then a surge when you connect the switch is what is causing your alternator failures.
 
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