Fuel gauge and sending unit

Will a electric fuel gauge and sending unit listed for use with 12 negative ground, work with a positive ground system? Could the connections be reversed??

Also what stops an electric fuel gauge from sending a electric charge to the tank causing an explosion?

Thanks,
Loren

Fuel gauge circuits are ground-searching. I.E. no volatage at the tank.

Don't know 'bout yer neg to pos thing, but I doubt it.

Allan

If the gauge is "thermal" (uses a little heater and a bi-metal strip to move the needle) it will NOT be polarity-sensitive.

If it uses a "magnetic movement" (electromagnets move the pointer) MOST LIKELY it WILL be polarity-sensitive.

There's no explosion in the tank 'cause the voltage/current/thermal mass involved in operating the fuel gauge prevent enough heating to light off gas fumes.

That being said, I have seen MANY fuel gauge senders and in-tank fuel pumps overheated with charred/burned wires 'cause of a short feeding too much current into a fuel sender or a fuel pump that failed and shorted out.

There's no explosion because the gas/air mixture in the tank is too rich (outside of the narrow range where combustion can occur).

From an engineering handbook...


Gasoline "Lower Explosive or Flammable Limit"
(LEL/LFL) 1.4%

Gasoline "Upper Explosive or Flammable Limit"
(UEL/UFL) 7.6%

Maybe, but would need to look at the unit to tell.

In a simple system (single wire to tank sensor)the Gauge has +12 connected to the gauge. The - side is ran to the sensor. The sensor is grounded (-) at the tank. The sensor (a simple resitor) had a arm that moved across it and it changed the voltage across the meter terminals.

However this is a simplie system. With all of todays funky rules it has likely changed.

Then they went to supplying voltage across the sensor (two wires, 1 voltage, 1 to meter, and tank used as ground). It reads the voltage at a pictular point on the resistor. In this case the meter did not have voltage supplied to it but read the voltage from the sensor with the other side of the meter grounded.

Now with all the plastic gas tanks, computers, and such they use three wires (voltage, meter, and ground). They may also have have electronics in there to reduce the actual voltage in the sensor itself (computer and such).

If it is a simple one wire system it may be possible to use it. "BUT" you would have to have the ability to reverse both wires at the gauge "AND" the case of the gauge not internally grounded (like a plastic case). Given you asked, I would not reccomend you try it.

As for why you do not get an explosion.

Gas does not conduct low voltages. Having this low voltage in the gas is not a problem. However, if the sensor shorts out (highly unlikely) it could be an issue if the tank was near empty. But in that case you would still need a certian amount of fuel/air mix to cause an explosion. In most (all if properly maintained) cases there is not enough air (all fumes) and it would just pop a fuse before anything happened.

BTW - Yes I have made one fail. While trouble shooting a faulty gage, I accidently shorted out the resistor with the pickup unit half out of the tank (tank half full). That sucker got red hot in a hurry. Fused pop'd and it never set of the fumes in the tank. Scared the be-geeb-ish out of me. I am pretty sure I got real lucky........

as i remember the guage is polarity sensitive and will not work on negative ground

the sender doesnt care