6 Volt alternator conundrum

S

Safari bob

Member
I have a friends Model A with a 6 volt alternator. After installing the engine, the amp meter showed no charge. I don't know if the problem was there before we changed the engine. Took the alternator to repair shop and when getting it back, it acted like a generator. The faster you went the higher the amps. Turning the headlights on, it stays below zero with the engine running. Have made several trips to the repair shop and on last visit, they put in a new regulator. It still operates like a generator.

In my Model A, I have a 6 volt alternator. Works just great. Today I swapped them. Putting my alternator in my friends car, my alternator acted like a generator. Putting his alternator in my car, it also acts just like a generator as it did in his.

The battery is hooked up correctly, positive ground. I added a new ground wire at he battery to make certain I did have a good ground. I disconnected the horn. Something is keeping the alternator from acting like an alternator and perhaps burning out the regulator as soon as it is hooked up. Any suggestions on what I could be causing the problem?
 
Safari bob said:
I have a friends Model A with a 6 volt alternator. After installing the engine, the amp meter showed no charge. I don't know if the problem was there before we changed the engine. Took the alternator to repair shop and when getting it back, it acted like a generator. The faster you went the higher the amps. Turning the headlights on, it stays below zero with the engine running. Have made several trips to the repair shop and on last visit, they put in a new regulator. It still operates like a generator.

In my Model A, I have a 6 volt alternator. Works just great. Today I swapped them. Putting my alternator in my friends car, my alternator acted like a generator. Putting his alternator in my car, it also acts just like a generator as it did in his.

The battery is hooked up correctly, positive ground. I added a new ground wire at he battery to make certain I did have a good ground. I disconnected the horn. Something is keeping the alternator from acting like an alternator and perhaps burning out the regulator as soon as it is hooked up. Any suggestions on what I could be causing the problem?
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I read somewhere that you can buy a generator that looks like an alternator.

(The extent of my electrical knowledge.) ;)

Tom will straighten us out..

Larry
 
Safari bob said:
I have a friends Model A with a 6 volt alternator. After installing the engine, the amp meter showed no charge. I don't know if the problem was there before we changed the engine. Took the alternator to repair shop and when getting it back, it acted like a generator. The faster you went the higher the amps. Turning the headlights on, it stays below zero with the engine running. Have made several trips to the repair shop and on last visit, they put in a new regulator. It still operates like a generator.

In my Model A, I have a 6 volt alternator. Works just great. Today I swapped them. Putting my alternator in my friends car, my alternator acted like a generator. Putting his alternator in my car, it also acts just like a generator as it did in his.

The battery is hooked up correctly, positive ground. I added a new ground wire at he battery to make certain I did have a good ground. I disconnected the horn. Something is keeping the alternator from acting like an alternator and perhaps burning out the regulator as soon as it is hooked up. Any suggestions on what I could be causing the problem?
Click to expand...

What size pulley are you using? Also, is the ammeter an off-shore manufactured reproduction?
 
"..............In my Model A, I have a 6 volt alternator. Works just great. Today I swapped them. Putting my alternator in my friends car, my alternator acted like a generator. Putting his alternator in my car, it also acts just like a generator as it did in his. ...................."

Funny you should say that because I have a generator that acts like an alternator. :D

Actually you are talking about a regulated generator or alternator vs. an unregulated generator or alternator. Are you sure the battery is good? It should show a fair amount of charge right after starting, then taper back to near zero after a few minutes. If the battery has done a lot of cranking, or had a drain on it, then the time will be several minutes before the charge tapers back.

What is the voltage at fast idle right at the alternator output?


 
I am talking about alternators. Both were working fine at one point. I know that because I had to borrow it from my friends car. Before I switched mine to my friends car, it acted just as you indicated, fair amount of charge right after starting, then taped back to near zero after. When the lights were turned on, it discharged momentarily and then back to zero. When installed in friends car, it acted as a generator. The faster the engine, the more amps it put out. I will check voltage at fast idle at the alternator output.

Can the battery work just fine with no apparent problem and still have an internal issue which might affect it? It is a one year old Interstate.

Thanks.

Bob
 
I would take a reading of the battery voltage, then read the voltage while it's cranking the engine with the key OFF. You should get something like 6.3 volts, and 5.0 to 5.5 volts while cranking.
 
Thank you Tom. I may have an answer to why the alternator that I have had at the shop isn't working properly.On the Nu-Rex Site , there is an alternator short circuit test. It indicates a short circuit in the alternator.

However the one that was working properly in my car that I then put in my friends car show no short circuit yet it acts like a generator. I think I had better pull the battery and take to the Interstate dealer for a check. I put a battery maintainer on it and it does not show a problem with the battery. Still looking for causes. I will check the voltage tomorrow. Thanks.
 
I'm with Mitch.
The Amp gauge is not useful, in fact I never look at them when trouble shooting. Run the motor at idle, off idle and under-speed. Off idle and above you should 7.5+Volts. I believe it was Mitch or Mike that pointed out they run hot and they do, voltage wise.

If you exceed 7.7 volts under high speed you have a VR problem. Really if should not rise above the VR set point (7.7V).

Ignore the amp gauge until you do voltage checks. For me as I'm lazy I do my voltage checks at the battery, if the voltage is correct say 14.5V on a 12V system I load the car and turn everything on, if it maintains that voltage I'm done. I don't much care about amps.

Keep in mind that the mechanical input to the alternator produces electrical output. That output is on a curve, the faster you spin it the more current you get until you reach the VR set-point. A hungry battery can demand that current.
If you have a battery charger with an amp gauge if is a good friend. But it on your battery and see what it is drawing. If it is drawing say 30 amps at 7.7V you have found out a lot.
 
Today I discovered that the cable between the battery and the starter was not completely tight at the starter. After tightening it, my alternator started working correctly on my friends car.

The alternator from my friends car did not work on my car. The Nu-Rex suggested test showed that there is a short circuit in the alternator.

Today, I installed a generator on my car and tomorrow I will do as Paul in CT suggested, look for another alternator repair shop.

Thanks for all your suggestions.
 
Willie Krash said:
I'm with Mitch.

If you exceed 7.7 volts under high speed you have a VR problem. Really if should not rise above the VR set point (7.7V).
.
Click to expand...

Thank you! This information confirmed what I thought about my alternator.

After noticing some odd light flicker, I decided to check things. Battery is charged and holds a load well.

Alternator output at driving speed rpm was 9.7volts, at idle it was unreadable DC, but over 20 volts AC.
 
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