voltage drop--12 to 6v - Inliners International Bulletin Board

I recently restored some guages in a 48 GMC and I want to drop the 12v system for the gas guage and temp guage to 6v. I purchased a voltage drop from the Car Shop and a ballast resister from a local auto parts house. I tested both with a meter and a 12v power supply. The problem, both read 12v on the downstream side. Maybe there is more to it. I am hooking the positive on one wire, on the other wire my meter, then the other end of the meter to the negative wire of the power supply. Shouldn't I get a 6v meter reading? Please help!!! Am i doing something wrong, do I need to have a load on the line or what?

A ballast resistor is designed to drop the voltage as current flows through it. The reason it does this is the resistor "coil" uses a specific type of wire that does not pass all of the electricity going into it. As part of the current is blocked, so to speak, heat is accumulated in the wire as a byproduct of the wire resistance. An example of this phenomenon is any heating element such as a stove burner or toaster element. If there is not enough current, then there will be no voltage drop. As a rule, guages use very little current and therefore can't use a ballast resistor. Those are designed for ignition coils that will use anywhere from 10 to 100 times the current of a guage.

What you ought to use is an electronic voltage reducer kit specifically designed to do what you want. I've seen them advertised for years in J. C. Whitney catalogs and other suppliers like that.

Do the instructions in the Car Shop kit say to wire it up as you've described? You will need to connect some load to it to test the system, but I get the feeling you probably shouldn't use your newly-restored gauges.

Hope this helps. Anybody else used a Car Shop kit?

------------------
David

Quote:

Originally posted by just a six:
A ballast resistor is designed to drop the voltage as current flows through it. The reason it does this is the resistor "coil" uses a specific type of wire that does not pass all of the electricity going into it. As part of the current is blocked, so to speak, heat is accumulated in the wire as a byproduct of the wire resistance. An example of this phenomenon is any heating element such as a stove burner or toaster element. If there is not enough current, then there will be no voltage drop. As a rule, guages use very little current and therefore can't use a ballast resistor. Those are designed for ignition coils that will use anywhere from 10 to 100 times the current of a guage.

What you ought to use is an electronic voltage reducer kit specifically designed to do what you want. I've seen them advertised for years in J. C. Whitney catalogs and other suppliers like that.

Do the instructions in the Car Shop kit say to wire it up as you've described? You will need to connect some load to it to test the system, but I get the feeling you probably shouldn't use your newly-restored gauges.

Hope this helps. Anybody else used a Car Shop kit?

Quote:

Originally posted by just a six:
A ballast resistor is designed to drop the voltage as current flows through it. The reason it does this is the resistor "coil" uses a specific type of wire that does not pass all of the electricity going into it. As part of the current is blocked, so to speak, heat is accumulated in the wire as a byproduct of the wire resistance. An example of this phenomenon is any heating element such as a stove burner or toaster element. If there is not enough current, then there will be no voltage drop. As a rule, guages use very little current and therefore can't use a ballast resistor. Those are designed for ignition coils that will use anywhere from 10 to 100 times the current of a guage.

What you ought to use is an electronic voltage reducer kit specifically designed to do what you want. I've seen them advertised for years in J. C. Whitney catalogs and other suppliers like that.

Do the instructions in the Car Shop kit say to wire it up as you've described? You will need to connect some load to it to test the system, but I get the feeling you probably shouldn't use your newly-restored gauges.

Hope this helps. Anybody else used a Car Shop kit?

I seem to remember that a good approach for voltage control in a gas gauge circuit is to put a Zener diode in-line. The diode will 'cap' the voltage at 6 volts (or what ever value you have purchased) and register the voltage changes as sent from the sender. I did it on a '47 Chevy truck. The gauge needs to receive the changes not just a steady 6 volts. This tidbit is from an old street Rodder magazine.--- Frump

Hello, Go to page 116 in the new "Speedway " catalog... everything you need is there.Paul