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Old 06-28-2021, 07:19 PM   #1
samsonized
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Default one wire alternator

just bought a 34 with a flathead it has a one wire alternator and the system does not seem to be charging does anyone know how a one wire alternator is wired into the original wiring

the car is 12v negative ground
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Old 06-28-2021, 08:18 PM   #2
1948F-1Pickup
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Default Re: one wire alternator

I have one on my '48 truck but I did not do the wiring harness myself.
I will tell you that one truly set up to be "one-wire" will need to hit self-exciting
rpm to actually start producing voltage. It depends upon the model as far as rpm but
800 wouldn't be unusual.
Bring it up to somewhere near there in rpm and get out your volt meter.....
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Old 06-28-2021, 08:49 PM   #3
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Default Re: one wire alternator

Quote:
Originally Posted by 1948F-1Pickup View Post
I have one on my '48 truck but I did not do the wiring harness myself.
I will tell you that one truly set up to be "one-wire" will need to hit self-exciting
rpm to actually start producing voltage. It depends upon the model as far as rpm but
800 wouldn't be unusual.
Bring it up to somewhere near there in rpm and get out your volt meter.....

The one wire on my 8ba charges as soon as it starts. I think it depends on the alternator but not sure. Grounded the alternator and ran one wire to the positive side of the 12 volt battery.
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Old 06-28-2021, 09:28 PM   #4
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Default Re: one wire alternator

From the battery post of the starter solenoid to the output post of the Alternator
run a 10 gauge wire. Start the engine, might have to rev engine to about 1,000 to
1,500 RPM to excite the alternator, if it is a one wire alternator.
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Old 06-28-2021, 10:15 PM   #5
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Default Re: one wire alternator

I had a GM single wire alt. on my '41. It had to be about about 1K RPM to start operating.I took it to a rebuilder as I was going on a trip to check it out. He somehow made it operate as soon as I started the car. Had a wire from starter Sol to alt.
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Old 06-29-2021, 12:53 AM   #6
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Default Re: one wire alternator

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The thing I love about looking at a flathead motor is that new gm alternator.



The good thing about an alternator is you don't need a voltage regular like a generator. It's built in. Could be a bad alternator.
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Old 06-29-2021, 04:28 AM   #7
51 MERC-CT
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Default Re: one wire alternator

Quote:
Originally Posted by samsonized View Post
just bought a 34 with a flathead it has a one wire alternator and the system does not seem to be charging does anyone know how a one wire alternator is wired into the original wiring

the car is 12v negative ground
If the Ammeter flow was not reversed, because of the new reversed polarity it will not read correctly but will show discharge when actually charging.
(the wire connections on the Ammeter may have to be reversed)
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Old 06-29-2021, 05:34 AM   #8
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Default Re: one wire alternator

https://www.powermastermotorsports.c...rnators_a.html

This site should help & give u some ideas.
-As said the 1 wire goes to positive side of battery.
-A smaller pulley will get the rpm on the alternator up to the speed required to start charging
-I don’t think a positive ground alternator exists so as said for ur gauge to work when converted to negative grounding u need to reverse the original negative / positive connection on your electric gauge to match ur 6 or 12 conversion to the neg ground alternator
- I believe there are external exciters that will let it charge immediately on any rpm.

https://www.powermastermotorsports.c...rnators_a.html
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Old 06-29-2021, 07:52 AM   #9
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Default Re: one wire alternator

Hi,
I have run and also installed one wire alternators and changed the regulator in them to make them one wire. A friend at work swapped regulator in a gm alternator and installed it on his WD Allis Chambers. It would not charge. We searched the net and found that in rare occasions that the alternator can lose its magnetism and won't charge. News to me as I had never heard of this. All is needed is to re excite it. I have copied and pasted the info. Good luck. Before you remove the alternator, first try to determine if a loss of residual magnetism is causing the loss of voltage. You can do this by flashing the field:

With the vehicle ignition in the “off ” position, remove the rubber boot from the alternator battery terminal and the rubber grommet from the small “R” terminal.
Take a small piece of wire and touch one end of it to the battery alternator terminal. Then touch the other end to the small "R" terminal. (Note: This may create a small spark, which is normal.)
Remove the wire and start the vehicle. The voltmeter should now increase its voltage reading to around 14 volts.
If the alternator isn’t charging, then re-check all connections and belt tension before removing the alternator.
Put the rubber boot and the rubber grommet back on.
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Old 06-29-2021, 12:06 PM   #10
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Default Re: one wire alternator

most gm style one wire set ups can be converted to 3wire. you may see a two post connector area not in use. Any auto store should have the connector with some short leads. All you need after that is a diode in line with positive wire and no more worries about exciting your charge system. Ken
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Old 06-29-2021, 02:57 PM   #11
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Default Re: one wire alternator

Most one wire alternators are converted GM units. They rely on residual magnetism in the rotor to turn on. Revving the engine will often turn them on, and charging is usually weak until the engine revs up. Usually there is a tab on the back of the unit that, when grounded, will kick the unit on. My '47 has a button under the dash connected to that terminal that will wake up a lazy unit. Alternators in modern cars are turned at a higher rate than most older vehicles can. That is why a smaller pulley can help a bit
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Old 06-29-2021, 04:15 PM   #12
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Default Re: one wire alternator

https://vintageautogarage.com/how-to...ts-free-guide/
If you fill out their form for converting to 12 volts they will e-mail you this book. It tells how to wire a one wire alternator
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Old 06-30-2021, 10:22 AM   #13
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Default Re: one wire alternator

Kits are available on flea-pay to convert a standard 12-volt Delco 10si alternator to single wire 6-volt positive ground type use. They come with all the parts & instructions to do that or a person can purchase the kit to overhaul a similar modified unit for repairs. There are U-tube videos as well for this.

The caveat on these is that all of the 6-volt internal regulators put out a set 7.5-volts so they have a tendency to over charge the battery. If a person runs with headlights on then that may help with this.

These alternators were originally a 12-volt 3-wire set up. The main stud feeds the buss through an amp meter if a person wants to keep an eye on the charge state but the OEMs used the warning light that was connected to terminal #1 of the two spade terminals through a dual connector. The other terminal #2 on the dual connector was for voltage sense which would be best connected to the battery positive connector (negative ground). The voltage sense wire would help with voltage regulation and the warning light in the circuit would excite the alternator as soon as the engine started as long as the warning light went out. The other end of the light circuit connects to the ignition switch for power. To make a one wire system from them, eliminates these two features.

Instructions on the modified 6-volt units state that sometimes one of the two spade connectors (terminal #1) needs to be shorted to ground (positive ground) to get it to excite initially. After that it should do it on its own when the rpm is raised to a certain point. A lot depends on what diameter the alternator pulley is. A smaller pulley diameter will lower the rpm that excites the alternator but this may not be advisable on high rpm engines. On a model A it can use a pretty small pulley but a V8 maybe not so small.

On a 12-volt 10si or 12si negative ground unit, the terminal #1 connector of the two pin plug may have to be touched to the Main power terminal after it's all connected up to do an initial excite on an alternator with little or no residual magnetism in the rotor. This would include ones with new rotors or older ones that have set on the shelf for several years. Personally, I would connect it back up three wire style to get most efficient function out of it.

Last edited by rotorwrench; 06-30-2021 at 04:20 PM. Reason: added info
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Old 06-30-2021, 11:27 AM   #14
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Default Re: one wire alternator

thank you to everyone for all your help
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Old 07-01-2021, 01:03 PM   #15
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Default Re: one wire alternator

A smaller pulley on the alternators will raise the rpm.
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Old 07-01-2021, 03:29 PM   #16
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Default Re: one wire alternator

Like rotorwrench, I prefer the three wire connection. On the alternators that Whitney sales, I have them wire them as a three-wire. That way you can wire them into a stock (gutted) voltage regulator to look all original.
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Old 07-01-2021, 04:16 PM   #17
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Default Re: one wire alternator

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Originally Posted by JSeery View Post
Like rotorwrench, I prefer the three wire connection. On the alternators that Whitney sales, I have them wire them as a three-wire. That way you can wire them into a stock (gutted) voltage regulator to look all original.
I am running a 1 wire alternator thru a gutted regulator that looks stock.
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Old 07-01-2021, 04:25 PM   #18
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Default Re: one wire alternator

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Originally Posted by 51 MERC-CT View Post
I am running a 1 wire alternator thru a gutted regulator that looks stock.
Yes, you can run the 1-wire that way, I just prefer the way the 3-wire works. Both work, there are just different advantages between them.
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Old 07-02-2021, 12:01 AM   #19
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Default Re: one wire alternator

Yeah, but the op's vehicle is a 34 ford, no regulator, a single wire hookup is standard; originally to the cutout.
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Old 07-02-2021, 08:23 AM   #20
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Default Re: one wire alternator

when I ran the GM alternator I ran the #2 (voltage sensing wire) as close to the battery as possible (battery side of the starter relay). There is [generally] a .6-.8 voltage drop (differential) between that and just looping the #2 terminal straight to the output terminal.
Don't sound like much BUT it makes a world of difference how the voltage regulator reacts at an idle.
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