Adjusting a Voltage Regulator for an 8-Volt Battery

June 1, 2009 | By Bond Hanson

This is in response to the March question from a reader who wanted to know if he can put an 8-volt battery in his 1955 Thunderbird “without changing anything.”

No parts need to be changed to convert to an 8-volt battery but the voltage regulator needs to be adjusted for it to be kept charged.

To adjust the regulator, you need a voltmeter that reads in tenths of a volt and it would be best to have a shop manual.

These instructions are for the common 3- unit regulators—if you have a single cutout or 2-unit regulator, you’ll need to use a shop manual and adapt these procedures.

The battery needs to have close to a full charge. A DC model train power supply will do the job if you set it to a voltage reading of 9.5-10 volts when it’s hooked up to the battery. A fully charged 8-volt battery should read around 8.4 volts.

1. Remove the cover on the voltage regulator. If it’s riveted on, you can drill out the rivets from the bottom side and then use sheet metal screws to reattach it.

2. Hook your voltmeter to the battery and start the engine.

3. You will need to adjust the voltage regulator portion first and then the cutout. Don’t make any adjustments to the unit with the heavy copper wire wound around it—it’s the current regulator and resetting that can cause the generator to burn up or charge at too low a rate.

4. The voltage regulator is the unit that is wound with small copper wire and the contacts are normally closed with the engine off. You will want to increase the tension on the coil spring on the side a little. The adjustment is done by either a screw on the spring bracket or by using needle nosed pliers to bend the hook holding the spring on the end closest to the base of the regulator.

5. Start the engine and keep it revved up to a fast idle. Carefully put the cover back on and note the voltage; it should be between 9.2 to 9.5 volts with the cover on. You can then make more adjustments as needed but if the cover is off the difference in temperature will give you an incorrect reading. I always just hold the cover on with my hand to check the readings. Be careful when putting on and taking off the cover so you don’t cause a short circuit.

6. The last thing to do is adjust the cutout. It’s the section that has contacts normally open with the engine off. You will need to have the engine running at a slow idle. Increase the spring tension on the cutout a little. You will be slowly increasing speed until the cutout closes 2 or 3 tenths of a volt above battery voltage. The object is to have the cutout open when the engine slows down to idle and be open when the engine is turned off, and when the engine is raised above an idle, the cutout will close and the generator will start to charge. (If for some reason the cutout contacts are accidentally closed with the engine off, the battery will discharge and also the generator might need to be repolarized—see a shop manual to do this).

I first started dealing with 8-volt conversions in the 1960s when people were still driving cars with 6-volt systems. The starter will actually last longer as the car will start much quicker and there will be much less heat and wear. Bulbs have been designed to run on 8 volts for years (sometimes they will have 6-8V written on them). Older cars develop small amounts of resistance in the connections through the years so an 8-volt system helps in that respect also.

As an aside, I now have a car with a hydraulic pump that operates the power windows and seat. I would have converted it to 12 volts but instead went to 8 volts to make things simple.

Bond Hanson

Retired garage and Ford dealership mechanic, Florence, Oregon