VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1929-1932 6 volt alternator showing discharge

I just fired up the '31 with the new 6volt alternator installed. I didn't expect the amp gauge to still work, but it does. It's showing a 5 amp discharge. I turned the lights on to check and it went to a 10 amp discharge. Is this correct or is it that the amp gauge doesn't read correctly with the new alternator?

The way it is wired is that I have one 10 amp wire run from the stud on the back of the alternator straight to the stud on the starter where the battery is connected, as per the directions.

I put on a 6 volt alternator on my 31 and it did the same thing. There is a self exciting feature built into the alternator and you have to go well above 1000 rpm to get it started. There is a plug that you can buy from the filling station and you connect it to power from the battery and it will feed back to the alternator and get it charging without getting to 1000 rpm. See your instructions or contact the provider of the alternator for instructions on wiring the alternator so that you don't need to get to 1000 rpm. I also put one on my 53 and it starts on its own without the extra plug. At least that is how my alternators work.

I found my e-mail that I got from the provider of my alternator. It may help you to understand how to connect your alternator.

I have the wire connected so that it will receive power only after I turn on the ignition switch on. When ignition is off the power from the battery is cut off and will not feed back to the ignition and prevent the motor from stopping. My first attempt at connecting did exactly that and I was not able to stop the engine. Now as soon as the engine starts the alternator starts to charge the battery.

Email to the provider of my Alternator requesting clarification of connections
I purchased the following alternator from you. D110SiSE6V35 What I need to know is when I connect the ignition wire to the #1 terminal to activate the alternator, this connection will put 6v of continuous power to the alternator. Is this correct or should the power to the #1 terminal be temporary on startup. Continuous makes more sense to me, but is that correct. Please help.

Paul

Answer from Provider
You keep it continuous. When the alternator is activated, it begins to use the power it generates to keep the regulator going. The voltage going into the #1 terminal drops to zero, which is why the charge light goes out in your dash.

Sometimes power will feed back through this #1 into your ignition, preventing your vehicle from shutting down. If that happens, you need an anti-feedback diode in the line going to your #1 terminal.

Thank you for the reply. I forgot to mention that I did rev the engine to well beyond 1000 RPM to try to excite the alternator and it did not make any difference.

The company I purchased this alternator from makes Ford positive ground alternators. If they sent me the wrong one by mistake would it cause this discharge problem?

On a side note, I ran into the same problem with I put HEI in my wife's '71 Pontiac station wagon with a 455. Turns out that because I used a relay powered by the ignition in the line that runs straight from the battery to the HEI, it was back feeding through the alternator and I had to install a diode as well.

I tried revving mine well above 1000 rpm and it would not excite the alternator. I had to connect the plug to make it work. Once the plug was connected it worked perfectly. A discharge is natural if the alternator is not charging. I would try connecting a wire from the "+" directly to the alternator #1 terminal for just a second. That is enough time to excite the alternator. Again, I would recommend contacting the company that sold the alternator and ask them. I am almost 100% sure that you need to excite the alternator.

I had the same problems when I tried to set up my 31. I actually gave up trying to use it for over 1 year because of the problems. Then after some research and contacting the company I finally got the connections correct. I completely disassembled my unit to check and see if there were problems. Everything tested ok. Then I finally contacted the company by phone and they explained what I had to do and then things got straightened out. Even then I had to get clarification as to how to properly connect when exciting the alternator. Unfortunately instructions that come with the alternators are sadly lacking in how to properly connect them. I think the 6 volt alternators need a lot more than 1000 rpm to excite them.

Does it take 1000 rpm for the alternator or 1000 rpm for the engine? Because of the difference in pulley size it does make a big difference in engine speed.

I have used 6v alternators on cars, tractors and industrial engines that are self excited and they work, some are positive ground and some are negative ground.
Now for the simple instructions first alternator pulley should be 2 inch or less, wire on back of alt. goes to amp meter then from opposite side of amp meter to battery. this is commonly called a one wire alternator and will require some slight extra revs to excite.
This is how my 29 coupe has worked for years
If wire is run from alt direct to battery the amp meter will not show charge
Al

As mentioned by a3alf, the wire from the alternator should go to the back of the amp meter and from there to the battery. The way that you have it wired the amp meter is out of the loop.

Thank you everyone for the replies. I have installed one wire alternators on a '57 Chevrolet and '60 Cadillac and I did not need to add any other wires to get them to self excite. I'm not disagreeing because we may have just had different style alternator set ups, but I do know that it is possible, as was mentioned by another.

I was unsure of exactly how the wiring is laid out. It makes a lot of sense when I think about it that if I took the old generator wire off then the amp gauge couldn't possibly work correctly, so I wondered how others' worked, but knowing so little I just assumed it did. I also wasn't sure if I wired the new alternator into the amp gauge if it would damage the amp gauge. I thought maybe I would need to switch to a volt gauge to be able to hook it up this way.

I will take the 10 gauge wire, run it to the back of the amp gauge (the same side of the gauge that the generator went to) and run the other side to the starter and then I'll get back to you guys with what happens.

Steve and Paul --

Yup, Paul is correct in is answer. I have 2 types of so called "one" wire alternators. The only difference between them is one is a six volt and one is 12 volt. They are wired slightly differently.

The 6 volt unit has the power out terminal, and just above it you will see a plastic plug inserted in case. Looking at the alt from rear, under the plug, the left side is terminal #1 and the right side is terminal #2. The terminal #1 is attached to either the ignition switch or the coil to shut off power so the alt shuts down when key is turned off or the eng will continue to run. The terminal #2 has a short lead from it to the power out side. The reason mine charges instantly is there is a diode in the line to "fool the alt" into thinking that the system is already up to snuff so you don't have to rev the eng up to excite the alt. That is from terminal #1. I have that wire connected directly to coil.

The 12 volt unit is also a one wire affair, the difference as noted above by Paul as there is only the power out wire and the plastic plug is in place and the 2 terminals under that plug are not being used. The wiring diagram shows only that power out wire being attached to the amp gauge, thence from the other side of gauge, it goes to ign switch (battery side of switch) which ties to positive side of battery. Don't worry about amp gauge as amp gauges are not volt sensitive and they work on either 6 or 12 volts just fine. With this system, according to directions, you will have to rev eng to approx. 2000 rpm to get alt to excite and operate correctly. Paul's first post explains that properly. (probably better than I can)

With the 6 volt system I have in my 31 and 48, using those 2 terminals under the plastic plug, it works sweet. You can contact Fifth Ave Auto Parts and talk to them is you prefer the first system I mentioned and see if they have a "DA" plug to convert your present system to the other style I mentioned. Give them the number off your alternator when you talk to them.

Hope I told you right and didn't confuse you and the best to ya.

Jim.

Ah, I see. It was a new unit I bought from a company on ebay.

I tested the alternator today with a multimeter across the battery. When the engine was started it was putting around a little over 7 amps.

I found out after doing some research that you can run a one wire alternator through these old type amp gauges but it is necessary to run a shunt across the hookups on the amp gauge to keep from frying the gauge. A google search of amp gauge shunt will give more info than I can give here. It basically bypasses the dangerous part of the flow of amps around the gauge but allows just enough for the gauge to read.

I don't understand the need for the shunt. If the alternator is producing more amps than is on the scale (for example a 30 amp guage with an alternator capable of producing in excess of 30 amps), then some provisions must be made. Did you mean to say 7 volts vs amps?

If you are using a 37 amp alternator there should be no problem the amp meter will peg when first starting and then drop down.
I have driven our 29 for more then 6000 miles on tours this way and it still works fine.
Al