By Paul Shinn with Kevin Duffy
Video at https://www.youtube.com/watch?v=euUFrwWh_0M&t=3s
Parts Needed
- GM 12v Alternator, Model 10SI
- These are normally found at the salvage yard in late 70’s and early 80’s GM cars such as Camaros, Buick Regals, Pontiac Grand Prix and some Cadillacs. Use the photos here to identify the proper used alternator.
- 6v Voltage Regulator, J&N 230-12031 (Amazon)
- Positive Ground Rectifier, J&N PN 172-12004 (Amazon)
- Pulley, J&N GDR-5002 (Amazon)
- Extra insulated screws
- Cover plug for terminals on the voltage regulator
- Home-made jumper wire
Parts Note: The insulated screws and the cover plug may be difficult to source. Taking one of the screws to your local hardware store may provide you with the insulating washers that you need to make all three screws into “insulating screws.” The cover plug can also be difficult to source. Some voltage regulators come with a cover, so we suggest that if you have a choice, pick one that has the cover with it.
Necessary Tools
- Air or electric impact with a socket for the pulley nut
- 5/16” nut driver or socket
Alternators were invented in the early sixties to provide a more consistent and reliable power source for running car electronics and charging the battery. The Model A generator is a good unit, but it can both undercharge and overcharge with regular use. It also needs regular maintenance to keep it working properly. So, changing your Model A to a six volt positive ground alternator is a good choice, although not an original part. If you use your Model A regularly, the alternator is a good choice. They say that “a generator is for show; an alternator is for go.”
The Model A parts suppliers can provide you with a proper six volt unit for just under $300. Paul looked at one of these and found that they are very similar to the parts and process that is described here.
This video shows you how to convert a typical GM 10SI twelve-volt negative ground alternator to produce six volts positive ground with just a few parts and a little time. So, let’s dive into it and see the process, tools and parts that are needed.
A GM 10SI alternator is very common unit that was used on millions of General Motors cars in the last thirty years. You can start with a used one from the salvage yard or you can get a new one to convert – it is up to you.
Procedure
- If you have a used alternator, clean it prior to disassembly
- Starting with a clean unit is important. Clean dirt and debris from the case.
- Disassemble the alternator
- Using the impact gun, remove the nut holding the pulley on the main shaft
- Remove the pulley and the fan
- We will reuse the fan and now is a good time to clean it and maybe even paint it.
- Using the 5/16” nut driver or socket, remove the four bolts holding the two halves of the alternator together.
- Make some reference marks with a Sharpie on the outside of the case halfs. They need to be reassembled in the same orientation to each other.
- Break apart the two halves. You will probably need to tap around the casing with a small hammer.
- Remove the rotor assembly (armature) from the front half of the casing by pushing it out by the pulley shaft. Do not lose the washers – you will need it later.
- If you want to change the front bearing, this is the best time to do it.
- Clean the rotor at this point. Make sure that the copper surfaces on the shaft are clean and shiny with no metal shavings. This copper surface is where the brushes ride to transfer electricity, so they must be smooth and shiny.
- Remove the 12-volt components from the other half.
- Remove the three 5/16” nuts that hold the stator to the rectifier. The large circle of copper wires. Remove it and put it aside, but make sure that the wires you just disconnected don’t get bent out of position – they need to go back in the exact same place.
- At this point the brushes have probably pushed out of their spaces with the springs that hold tension on them. Remove the brushes and springs, then put them aside. You will need them later.
- Remove the three screws that hold the voltage regulator in place. The screws with the rubber washer on them are the “insulated” screws – this is important later. With the screws out, you can then remove the “triode” or triple diode. We will reuse this.
- With these screws out, you can remove the piece that holds the brushes in place. It’s best to prepare this piece for re-installation now as shown in the video. Basically, you put the brushes and springs back in, then insert a piece of wire to hold the brushes in place during reassembly. Take the video to about 3:40 to see how this is done.
- Remove the voltage regulator and the rectifier. You will not be reusing these but instead putting in the new parts.
- Assembling your 6v Positive Ground Alternator
- Install the new 6v Positive Ground rectifier. Reuse the hardware that hold the old one in place.
- Set the 6v regulator in place.
- Install the brush holder with the wire installed. The end of the wire should stick out the back of the alternator so that you can pull it out later and release the brushes.
- Insert three INSULATED screws through the brush holder AND the voltage regulator.
- Install the jumper wire that you made. This wire is there to excite the alternator to start working when it starts spinning. (Otherwise, you would need to run another wire to the alternator – an exciter wire. This makes it a “one wire” alternator.). This wire goes between the rectifier and the voltage regulator. Make sure you use the proper terminals for this! (Go to about 6:40 in the video for this.)
- Reinstall the triple diode in the same location as they originally were installed. Do not put the three nuts back on the rectifier yet.
- Tighten the three screws holding the voltage regulator in place. Made sure that all three have insulator washers on them.
- Set the stator back into the housing with the three wires on the three studs for the rectifier. Reinstall the three nuts to attach the stator to the rectifier.
- Make sure all fasteners are tight inside the alternator.
- Reinstall the armature into the casing using the same washers.
- Reinstall the front case to the rear. Use the marks that you made on the cases to properly orient them.
- Attach the halves together with the original screws.
- Put the washer back on the shaft. Reinstall the fan onto the shaft.
- Install the new pulley to the shaft with its nut.
- Pull out the wire that is holding the two brushes in place. This allows the brushes to touch the copper on the armature.
- The two terminals on the rear side of the alternator are not used. Cover them with a rubber plug.
You are finished. if you have an independent alternator/starter rebuilder shop nearby, you can take your creation there and have them test it for function, just to be sure.
Happy Motoring!