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Thread: 6-volt to 12-volt Conversion; The Easy Way

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    Super Moderator LarrBeard's Avatar
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    Nov 2014
    Ft. Wayne, IN

    6-volt to 12-volt Conversion; The Easy Way

    I had a private message from BigFishDave in Colorado asking me about doing a 6-volt to 12-volt conversion with a new stock harness. I worked with him to figure out how to make the conversion. BMorgil had made a similar conversion to peeJ (his CJ-3A) and he gave me a lot of information about one-wire alternators.

    What alternator should I use?

    The simplest alternator to use is a “one-wire” alternator. These are 60-amp Chinese rebuilt/remanufactured Delco 10si units available from just about every auto parts box store. Most will have a two-pin plug in addition to the big threaded post that provides charging current to the electrical system. The Driveworks 7127-3AV is typical of these units. (See second attached photo)

    My ammeter only goes to 50 amps, will I burn it out with a 60-amp alternator?

    Most likely not. A 60-amp rating means that the alternator can put out 60-amps if needed; it does not force 60-amps into the electrical system. The only time the alternator will deliver its full current capacity to the electrical system is when the battery has been pulled down by an extended cranking period or when the battery has been discharged. It may pin the ammeter for a short time, but it is unlikely to damage the ammeter.

    What do I connect to the two pin plug on the alternator?

    If you are converting a vehicle with an ammeter - you connect nothing to the two-pin connector. If you are converting a vehicle with a charge indicator light, you will connect it to one of the pins in the two-pin connector. If you have only a charge indicator light in your vehicle’s instrument cluster, make sure that the unit you buy has a charge indicator function. (The Driveworks 7127-3AV does have this feature.) Check the instruction sheet with the alternator to make sure you connect the proper pin.

    what do I do with those three wires that were connected to the generator?

    The generator was a three terminal device. Charging current was provided from the armature terminal (“A” or “ARM”). This terminal will be the largest of the three terminals on the harness and in many Jeep harnesses, it was a blue wire/white tracer; about # 10-gauge. This wire will connect to the battery terminal of the alternator. On the alternator this terminal may be marked as “B” or “BATT” or unmarked, but it is the big threaded post.

    Another wire was the ground wire, a black wire/white tracer with a smaller ring terminal. This wire was connected to the frame/case of the generator and was a power return that went up to a frame ground somewhere near the original voltage regulator. On the alternator there is generally a screw that connects to the alternator case. Connect the original ground wire to this screw. It is good practice to add another ground wire from under this screw terminal to a good ground point on the engine. Having good power returns throughout the electrical system keep a lot of problems from happening.

    The third wire is the old field lead to the generator, a yellow wire/blue tracer with a small ring terminal (the size of the ground terminal). This wire will not be used with the new setup. You can cut it off, or a better idea, turn it back and secure it with a cable tie.

    Now, what about the other end of these wires? They all end up at the old voltage regulator. On the voltage regulator there are three screw on terminals. On most regulators, the bottom terminal is the ARM or A terminal where the blue/white wire from the alternator ends up. The middle wire is the F or Field terminal ( again, not used) and at the top of the regulator is a red/white wire (#10-gauge) that heads back up under the dash.

    You will not use the old voltage regulator, so you can leave it in place just for looks or you can repurpose it. The blue/white wire from the alternator gets connected to the red/white wire going back up under the dash. The simplest way is just to strip them back and add a crimp sleeve. This wire is going to handle all of the current for the whole vehicle system (except the starter), so you need to make a good connection.

    Now, a word of caution. The new alternator can, when it needs to, put out about half-again as much current as the original generator. There is a circuit breaker incorporated in the light switch assembly, but it is a thermal breaker that has to heat up to make it open. It is slow. If you get a wrench or screwdriver somewhere it shouldn’t be, wires can start to smoke before that breaker opens. I strongly suggest that you add a fuse between the new alternator and the existing wiring harness up under the dash.

    There are a lot of in-line fuse holders that can go between the blue/white wire and the red/white wire. I suggest a 60-amp slow blow fuse. That fuse will carry the 60-amp alternator current for a long time (hours) but if you get across things the wrong way, it can go in a second or less.

    But, BigFishDave from Colorado come up with an neat and elegant solution of how to add a fuse and keep the vintage look of the original vehicle. Here is a fuse holder he found:

    He stripped the old relays out of the voltage regulator and mounted the fuse holder in the regulator case. (See first attachment)

    The red/white wire still goes to the BATT (top) terminal, the blue/white wire goes to the bottom (ARM) terminal and since it was right there, he reconnected the yellow/blue (FLD) wire back to the middle terminal. (The FLD lead goes nowhere inside the box, this is just a tie point).

    It makes a very neat installation for the 60-amp fuse. And, it adds a bit of Jeep mystique - folks will look at his ’52 truck with the F-134 and the new alternator and wonder “What in the world is he doing with that voltage regulator AND an alternator?” (See third atachment)

    Is there anything else I need to know about my new alternator?

    One wire alternators are self-excited machines. Like the generator it replaces, it depends on residual magnetism in the pole pieces to get it started generating current. When you start the vehicle, you will need to “blip” the accelerator to get engine speed up to about 900 to 1000 RPM. Once the alternator spins up (alternator speed about 2000 RPM because of the smaller alternator pulley size), most alternators it will maintain a charge even down at idle speed. Your ammeter will tell you exactly what is happening and if you get to a discharge condition, run at a faster engine speed for a while. (This could happen in a parade…)

    What about the starter?

    The simplest thing is to leave the original 6-volt starter in the vehicle. Since it is going to spin a lot faster, I would suggest having it looked over at a good auto electrical shop to check brushes, armature, bearings and bushings. It’s not going to be engaged long enough to overheat. Remember, that thing is almost 25-pounds of iron and wire.

    But, there are a lot of 12-volt starter options, just make sure you don’t get into a tooth mismatch problem between the Bendix drive and the flywheel. Mismatched teeth make grinding sounds and metal chips and shavings!

    Do I need to replace gauges?

    If you decided to rework gauges, there would be more involved than just the gauges themselves. Each of the electrical gauges (fuel, oil and temperature) have a sending unit associated with them. The gauge and sender are designed for the original 6-volt system, so both units would need to be replaced.

    The most straightforward approach is to use the original gauges and senders. Since the gauges will either read wildly incorrectly or even burn up with the 12-volt system, the best approach is to add a voltage regulator between the ignition terminal of the ignition switch and the power to the gauges.

    In the 1951 through 1956 Jeeps, there was an instrument cluster voltage regulator added to keep the gauge readings steady as electrical system load changed. This original regulator will not last long if you try to run it with the 12-volt conversion. (See fourth attachment)

    The cluster operated at about 5-volts. For the vehicles with the newer clusters, I suggest a 5-volt regulator similar to this one:

    In an older vehicle (1946 through 1950 1/2) I suggest a 6-volt regulator like this:

    Do I need a 12-volt coil, points and condenser?

    You will need to change the original 6-volt coil to a 12-volt coil. Many 12-volt coils are intended to use an external ballast resistor, so unless you plan to add an external resistor - make sure your replacement coil has an internal resistor. The good news is that “points is points”; you don’t have to change points just because you have converted to 12-volts. The same for condensers; you’ll use the same condenser for 6, 12 or 24 volt systems. While you’re working on the Jeep and have your hands dirty, this would be a good time to do an ignition tune-up - take a good look at spark plug wires too.

    What about lights and lamps?

    Yes, all of the lights and lamps will need to be changed. 12-volt headlights are going to give much better nighttime illumination. Don’t forget the cluster lights and the little high-beam tell-tale light.

    Good Luck!
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