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1957 Tbird generator


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I finally got to have some fun driving my Tbird around town.  I stopped to get some gas and then could not start the car and had to get a jump.  Once I got home I connected a volt meter to the battery and jump started the car again.  Driving around town the volt meter would read 11.8 volt  for a while (even at RPM 2000)  then jump to 13.8 volts.  I drove the car for about 20 minutes, during the drive the voltage dropped slowly from 13.8 to 12.8 volts and held steady.  I was able to start the car with out a jump later in the day.  I am assuming that the brushes on the generator some how are intermittent?  Why would the voltage drop to 12.8 volts? (is this because the battery was charging)   I have a new voltage regulator.  I am assuming that the generator needs to be rebuilt ??  Is there anything else to check?  The battery is about 1 year old and reads and 12 volts after sitting for a day.   Thanks

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Hi TerryB, 

 

Belt is tight, cleaned contacts and wires for generator / voltage regulator awhile back.  The regulator is new and is the points kind. Battery cables are tight.  Suspect the brushes in the generator are sticky/worn.  Thanks for the suggestions.

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  • 2 months later...

The generator did test OK. I realized that when the contacts are closed the resistor looks shorted.  When I press on the contact to open them the resistance is about 35 ohms across the Arm and Field resistor.  A new regulator shows 35 ohms without having to press the contacts open.  I did clean the ground and all terminal leads with some sandpaper to ensure they have good clean contact.

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14 hours ago, Dave39MD said:

Maybe you don't have to on a ford system.

 

All generators need to have some residual magnetism to self start charging.  Polarizing magnetizes the field coil pole pieces so the generator will start charging. Brand does not matter, except in the method of polarizing.

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On 12/22/2018 at 5:43 PM, Denver T-Bird said:

When I press on the contact to open them the resistance is about 35 ohms across the Arm and Field resistor.

 

That sounds reasonable.

 

On 12/22/2018 at 5:43 PM, Denver T-Bird said:

A new regulator shows 35 ohms without having to press the contacts open.

 

And that sounds wrong.

 

I have no ford books handy, but IIRC 12v to the field terminal makes it charge, so whenever it is trying to charge, the field terminal would be shorted to the armature terminal by points in the regulator. When either the voltage or current gets too high, a relay would pull down (there's 2 relays, one for voltage and one for current), and remove the short.

 

Once the short is removed (points open). the resistor you are seeing (between the armature and field terminals), and another resistor to ground form a voltage divider for the field terminal, sending the field something much less than the 12+ volts it was getting when the points were closed. This makes the generator barely charge.

 

In operation, the voltage regulator relay probably vibrates very quickly between "hard charge" mode and "barely charging" mode as soon as the battery is getting close to fully charged.

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  • 3 weeks later...

Thanks to all for the suggestions.  I removed the generator and took 4 voltage regulators (1 original, 1 purchased in May and was tested and found bad and 2 units recently purchased online) to a new  shop.  The generator tested good, again. The 2 new regulators purchased online were verified bad.  The shop even removed the cover and made adjustments but could not get them to work.  The one I purchased in May was tested and found to be working fine.  Surprised to find that new units were bad from the start and the one the first shop thought was bad, is working.  Now all is charging as it should.  Thanks again!  

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