Questions on Generator to Alternator Conversion

[Bill Jewell]

Hello,

I own a 1930 vehicle that has been converted from 6 volt to 12 volt system. Also, the generator was replaced by an alternator. It is set up as a "one wire" alternator. Recently the battery went dead on it so since both the alternator and the battery were both old I replaced them both. I have not owned this vehicle for very long, but in doing some research I see that a "one wire" alternator requires that the engine must reach a high RPM before the alternator turns on and begins charging. I replaced the alternator with the identical alternator that was put on the car when restored 12 years ago (I believe it's a Delco 10-SI). My car has an amp-meter and I am noticing that the meter never reads charging. Here are my questions:

1) When I replaced the alternator did I need to do something to it for it to function properly as a "one wire" alternator?

2) How difficult would it be for me to convert this set-up to a three wire alternator system where the alternator comes on immediately when the ignition is turned on? How would I do this?

Thanks for any help that you can provide!

Bill

[Guest]

When I put a 6 volt single wire alternator on my Pontiac I could not get it to charge. I ended up putting a very small ! 1/4" pulley on the alternator and even then I have to rev the engine up once so the alternator kicks in. Once it is charging it will keep on charging even at a very very low idle speed. At first this bothered me but now I just blip the accelerator once every time I start the engine and everything is fine.

[37_Roadmaster_C]

Bill,

I am not sure of this, but I think that the conversion to a three wire alternator would be as simple as bolting it in the mounts, connect the charging wire you now have to the output terminal and connecting the field wire to the ignition switch, this wire needs either an idiot light or a resistor in it to funcTion properly. The third wire is a sence wire to help keep the charging voltage regulated. It can be hooked up to the main output in this case. Google 'alternator wiring' and you will find all kinds of info on this subject. I would probably go this route as opposed to changing pullys and/or reving the engine to start the alternator charging.

Robin

Edited July 9, 2013 by 37_Roadmaster_C
To correct error and add info (see edit history)

[joe_padavano]

The "one wire alternator" is a cruel joke perpetrated by the automotive aftermarket. It is instructive to note that GM, a company always looking to cut a few pennies off the cost of building a car, NEVER used a "one wire" alternator setup. There's a reason for that extra copper.

Wiring a normal three wire 12SI or 10SI alternator is extremely easy. Be sure the alternator is a stock type set up for three wire connetion (some of the aftermarket one wire units have the terminals connected internally and cannot be used in a three wire system). The large wire from the threaded BATT terminal goes to the junction block. The wire from the No. 2 terminal on the connector also goes to the junction block. This is the "sense" wire where the voltage regulator senses the actual voltage in the system and regulates accordingly. It is possible to simply connect the No. 2 terminal to the threaded BATT post (I've done this myself) and the alternator will work acceptably, but the closer you connect it to the actual load point (to account for resistance in the wiring), the more accurate it will be. The No. 1 terminal should be connected to the GEN light if you have one. This is an important part of the wiring and the one left out in the one wire conversions. The SI-family alternators require the resistance from the GEN light bulb to actually turn on the voltage regulator at idle speeds. If you do not have a GEN light, then you should connect this wire to a +12V switched source with a 35 ohm resistor in series to emulate the resistance in the bulb. NAPA sells a conversion harness for these alternators that includes the resistor. This drawing should help understand my explaination.

Edited July 9, 2013 by joe_padavano (see edit history)

[Rusty_OToole]

The 1 wire alternator was made for bulldozers, tractors and similar non automotive use. It will function on a car but as others pointed out, you have to gun the engine up to 2000 RPMs or so, for it to kick in. After that it will function normally.

The standard alt has 3 wires, 1 to the battery, 1 to keyed power (feeds the field coils, only when the car is running) and the third for the idiot light.

The only difference between the 1 wire and 3 wire is the voltage regulator which is inside the alternator. You can change one to the other by changing the regulator, or by taking your alternator to an auto electric shop or rebuilder, and having it changed. You don't have to buy a whole alternator.

[joe_padavano]

The standard alt has 3 wires, 1 to the battery, 1 to keyed power (feeds the field coils, only when the car is running) and the third for the idiot light.

Again, just to clarify, the third wire isn't just "for the idiot light". The SI-family alternators use that wire to actually turn the regulator on at low speeds. That's why vehicles without an idiot light (in other words, with a voltmeter instead) still need that wire connected to a switched 12V source through a resistor that duplicates the resistance of the idiot light.

I hadn't thought about the heavy equipment use of the one-wire alternator before, but it makes sense. Typically these engines run at a constant higher RPM (2000 or so), so the lack of charging at low speeds isn't an issue. Quite different from driving a car in stop and go traffic.

[Rusty_OToole]

Joe you are right I was trying to simplify.

[joe_padavano]

Joe you are right I was trying to simplify.

I understand. Unfortunately I've found over the years that if a post on line can be misinterpreted by someone, it will be. For example, I could envision someone reading your post and thinking, "now I have to install an idiot light instead of using my voltmeter." That's why I try to be complete in my responses - not that I always am, of course...

[startergenrebuilder]

I'd like to try and clear a few things up. First thing, the RPM's on tractors that people throw these one wire alternators a lot of times on is actually even lower than the automotive applications. As for solutions to your problem. I carry a newer version of the one wire regulator that kicks in a lot lower than the old versions. It wires in totally different, but I've had good luck with them. The problem is that turn on speed is largely determined by the windings inside of the alternator and you have no idea what combination of windings are in each alternator unless it gets tested after installing regulator. The other option for repairing yours is installing a 3-wire regulator like has been discussed earlier. I carry a plug that plugs in to the 3-wire regulator. One wire loops over to the battery stud on the alternator and the 2nd wire comes as a long lead with a diode in it that needs to be wired in to a keyed ignition source. The reason for the diode is so you don't backfeed your ignition and keep the car running when you try and shut it off. It's a handy little kit with plug and leads and it installs very easily. There are some better low RPM 1-wire solutions, but you are dealing with the most common one because they're cheap and easy to come by. If anyone has other questions, feel free to contact me.

Good Luck Everyone!

-Jason

[joe_padavano]

...I carry a newer version of the one wire regulator that kicks in a lot lower than the old versions. It wires in totally different, but I've had good luck with them...

OK, I'll bite. If it's a one wire alternator, how does it "wire in totally different?" There's still only one wire. If you mean it is wired differently INTERNALLY, then I understand, but your statement as written is confusing.

The beauty of a stock three wire 12SI is that parts, including the regulator or a complete alternator, are available at any parts store in the country at any time of the day or night.

[startergenrebuilder]

Joe,

Sorry for being a little vague. The wiring differences are all internal. Still fairly simple to install, the regulator comes with a instruction sheet and diagram. Being a 1-wire, it's still the same on the outside.

Quoted from above: "The beauty of a stock three wire 12SI is that parts, including the regulator or a complete alternator, are available at any parts store in the country at any time of the day or night."

Keep in mind that this "beauty" has put a lot of knowledgeable electrical rebuilders out of business. These all hour of the day parts stores carry Mexico and China remanufactured units and the techs at these stores are usually not very good for technical advice if your are in need. I hate to sound like a car salesman, but it's better for all of us if you can wait for regular business hours during the week and go see a local rebuild shop. In my opinion, you'd be better off trying to support your local Carquest, NAPA or other locally owned parts store. I know they don't usually carry the same late night and weekend hours, but I feel it's better option for everyone in the long run. Your luck of getting some good advice and technical help as well as having better testing equipment to diagnose your problem is far better at a rebuild shop also. Just my two cents.

You should be able to find the regulator I was referring to earlier at most rebuild shops. Ask for an AC turn on self exciting 10/12SI regulator.

Good Luck. Feel free to contact me if you have any questions.

-Jason

[joe_padavano]

Jason,

Thanks for the clarification. Do you have a part number for that regulator? Is it an AC Delco part?

... but it's better for all of us if you can wait for regular business hours during the week and go see a local rebuild shop.

Tough to do when I only have weekends available to work on the car. Until recently the local NAPA stores were closed Sundays and only open until noon on Sat. Most close at 5 or 5:30 during the week. When you don't get out of work until after 6:00, it's tough to patronize them. On the other hand, I can order from Rockauto and the part shows up on my doorstep two or three days later, no muss, no fuss. Frankly, I've rarely gotten useful info from the guys working at an auto parts store. I usually need to research what I need first, then just order a part number. I've also found that there are many errors in the computerized parts databases that they use (example: most parts catalogs incorrectly show that Vista Cruiser wagons use the same ball joints as full size Oldsmobiles, instead of the correct Cutlass ball joints). One needs to be informed and not just trust what they tell you.

[startergenrebuilder]

Joe,

Delco (as far as I know) never made 1-wire regulators. I doubt you'll find the AC turn on regulator anywhere except through a rebuilder. I'm not sure what number they would use, it depends on who they buy from, but there is no AC Delco numbers and I don't know of any Napa or Carquest, Standard Ignition numbers.

I agree with your parts store guys knowledge comment, I was referring more to the starter and alternator rebuilder guys shop. Although I've heard some horror stories of dealing with some of these guys as well. I agree with you, do your homework and be informed. My only point was to try and support the local guys if you can. I understand the busy schedule thing. I just don't like the idea that were moving towards a nation of websites and warehouses. I see it often, guys want me to be there to test an alternator or help them troubleshoot a problem, but then they'll turn around and cut my throat for 10 bucks saved on an import unit over the internet. I'm not looking to start a war here, just offering my opinion from my perspective. I see your side as well.

-Jason