I think I know the answer to this..... I am doing some wiring on a 40 something Chev 1 ton. Converting to 12V. Question, Will I need to drop the voltage to the fuel level Gauge? Thanks, Frank
yes. Only the amp gauge doesn't care. But if you use a high amp alternator your going to peg the amp gauge.
Ohms law, Voltage = Amps x Ohms. Or an easier way to remember, Victory over Automotive Repair. Your Chevy should have a resistance of 0 to 30 ohms. o ohms when empty. 30 ohms when full. The sending unit itself does not care if it is 6 or 12 volts. It just gives a resistance to ground. Your gauge does care and will not read correctly with the higher voltage. .4 amps @ 12v .2 amps @ 6v
Absolutely. It is advisable to use a solid state voltage drop rather than a resistor due to the same electrical principle stated above.
Well, this is going to sound like heresy - but the answer to your question is NO! The fuel gauge circuit is a balance coil circuit, completely unaffected by voltage. That's why when you have temporary voltage spikes, or drops (such as turning on your headlights) you won't see your gauge fluctuate. The circuit draws a few milliamps and 12 volts won't hurt the coils or the sender at all. If you go to the stovebolt site and do a search you can read many stories of guys who have been running 12 volts to their stock fuel gauges for years with no issues whatsoever.
The stock 6V gauge will read full @ .2 amps and a half a tank @ .4 amps. If you supply the gauge with 12v it will only read half full with a full tank of fuel, .4 amps. So essentially the gauge will only function on the lower half of its scale. That does not sound bad, you just have to remember that half is full and a quarter is half. The problem starts when you run your tank low. Remember when empty you have Zero ohms. At 1ohm your gauge will have 6 amps with a 6V supply. At 12V that same 1ohm resistance causes your gauge to receive 12amps. This will shorten the life of your gauge.
onthefritz - your numbers would be right if you were applying the 6V or 12V directly to the sender wire - but that's not how a gauge works. The voltage is connected to one side of the gauge, and then inside the gauge are 2 opposing coils which the current flows through before it gets to the sender wire. The gauge drops most of the voltage, the sender has very little current flowing through it. Look up a schematic for a balance coil gauge and you'll see why it doesn't matter what the input voltage is.
Here's a typical fuel guage. You can see that the voltage first goes through a coil, then it divides between the tank rheostat (the sender) and an opposing coil in the gauge. Only a fraction of the input voltage is available at the sender wire. If the voltage is raised, the 2 opposing coils flow more current (or less, if the voltage is lowered) but the pointer remains in the same position because the opposing fields react accordingly.
I'm trying to find the problem with my fuel gage and found this page. I have a 54 Chevy 3100 but with an engine from a 58'. I'm "assuming" this truck was originally a 6 volt but is now a 12 volt system. Your example and description of gas gauge workings makes sense but why when I am looking for solutions for my gauge a lot of sites are recommending to have a resistor installed to gas gauge when a 6v to 12v conversion has been made and if I want to buy a new gas gauge they always ask what voltage your system is?? Just trying to understand. Thanks for any reply Tim N
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