The Stovebolt Site Forums The Shop Area The Electrical Bay What is a reducer?

Rather than ride someone's post about trying to get a 6 volt gauge run on 12 volts I would like to know. What is a reducer? I know and work with voltage regulators and zenor diodes but this reducer is a question mark. I think they are talking about a resistor. Yes, you get a voltage drop across a resistor but then you must know what R(t) is, which is the "pickle". If it is indeed a resistor how on earth do the guys figure R(t)? Thanks

I do not know enough about electronic to know how they work but here is a link to one being sold and it does give some specs. My personal guess is these devices do not make you gauge read 100% correct they just keep the gauge from buring out and let you know you have some fuel in the tank
reducer

I don't know a thing about electricity, or reducers, but I have been told by people who have used them that they didn't have much success with them. Maybe they were like me, and didn't know how to properly hook one up. Allen

R(t), R= resistance, what is t? I use my original fuel gauge with 12volts, It reads full for a long time, then goes to empty fast. The sending unit in the tank has a variable resistor in it, that needs to be changed to make it work right, to adjust the range of the gauge. Putting a resistor in series doesn't quite get it. You can read the resistance of the sending unit with an ohmmeter. with the gauge disconnected, full tank, and empty tank. divide each of those readings into 12(12volts) to get the current range. Somehow I came up with this chart, I think from studying the reducers available in catalogs, it was years ago. Run 6 volt accessories from 12volt system. 1amp load=6ohm 6watt, 1.3amp load=4.5ohm 7.8watt, 2amp load=3ohm 12watt, 4amp load=1.5ohm 24watt, 8amp load=.75ohm 48watt, 12amp load=.5ohm 72watt. Using a dropping resistor is not efficient and they get hot!

A reducer, IINM, is a heavier duty resistor that will reduce the voltage from 12v to 6v.

One would have to be installed before the fuel gauge for it to read correctly, as the gauge is basically voltage meter that has a top end at 6 or 7v.

If you feed it 12v, it certainly won't read correctly, and may burn up.

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Yes, a dropping resistor gets hot. It's supposed to. That's the way resistors work. They convert the excess electricity to heat.

A Radio Shack three terminal voltage regulator can be adjusted, with resistors and a couple of capacitors, to provide exactly six volts to the gauge, regardless of the input voltage. Total cost should be less than five bucks.

Or, spend $5.99 plus shipping for a fuel gauge voltage reducer and never worry about whether or not one is truly needed after a 6v to 12v conversion. This is a lot cheaper than having to buy a new gauge.

Beltfed asks a key question at the top of this post. The value of R(t) - the total resistance of the circuit, including the guage windings and the sending unit, must be known if a voltage reducing resistor is being used. Since the sending unit's resistance is constantly changing, there is no one dropping resistor value that will maintain a constant 6 volts at the guage since R(t) is in a constant state of flux.

A mini- DC/DC convertor or, possibly a zener diode, is the only thing that I can see that would do that. My belief is that the "voltage reducers" available from our suppliers are simple resistors that give a "good enough" result even though the voltage is fluctuating at the guage. If someone has one of these on their rig, read the voltage at the guage when it's full, and then again when empty and let us know. My thought is that it won't be 6 volts in both cases.

I've been using the reducer tim posted above for about 24 years.It works great and has lasted a long time.I could'nt tell you any of the electrical values for the resistor.It would be cool to say you built your own .
Good luck !!

The cheaper one is probably a 6.2 Volt zener.

Yup! Looks like a zener to me - that'll work.

OMG just hearin the word Zener makes me shudder & have flashbacks to the horror of my Dads 67 Triumph motorcycle I restored and fought with the charging sysytem for like ever I finally got rid of that darn thing an went with a electronic upgrade replacement .

The Brittish bikes of the 50's - 70's had lousy electronics on them. Lucas wasn't called "The Prince of Darkness" for nothing!!

the zener diode you want is a NTE 5118A 6.V,5W $3 bucks at most electronic supply. or you can buy a "stud mounted" one for $20 bucks that does the same thing. stud mounted one needs heatsink to cool the other style uses air flow around it.

OK..So here is my Question..Does all these posts here mean ...My truck is a 12 volt..But my Guage and sender are for a 6 volt? And some how I must add a Reducer..I burned up my origanal Guage,and got one from Classic..I also am on my 2nd sender...My guage still does not work..and for cryin out loud its only 2 Dam wires..how can I be screwin this up..I was going to get a PO box and use some elses credit card so classic would not think I was Stupid. M /G

Mike wrote:


I'm laughing because sometimes the simplest of things bite you. Heck, I can fire up just about any ship in the world and get it from point A to point B, but give me a darn single cylinder 4 stroke lawn mower and you'll see some real cussing at times. Fortunately for me I now have someone cutting my grass and don't have a mower to cuss at anymore.

My Dog sometimes sits in the truck and watches me work..But when she sees me diggin into the cluster..and reaching for the clutch screw driver...she is out of there.

A replacement aftermarket 12 volt gauge is available,looks like the original.It's available from all the vendors . Depends on how much money you want to spend.

Ya I realized that after i posted..Double checked what I did by from the Vender I use. It was 12 V They actually take pretty good care of me..replaced a couple things I messed up...

on the hamb this week their is a great tech article on using newer gauge movements (bi-metallic vs magnetic) by using only the stock faces of the gauges (AD TRUCK) check it out. they use a irv from a mid 70's car to regulate the power.

The other thing to consider is power dissapation or Watts. Power is dissapated in the form of heat. That is why the voltage drop resistors run hot. Make sure that whatever system you chhose can carry the power away and maybe even help it with an aluminum heat sink. The formula for Watts is Voltage x Resistance of the circuit.

Can I just by-pass my Guages...and install gauges below my steering wheel? Use the same Oil presser line... ammetter red and Black.. and gas gauge wires and Temp. Guage. In other words use what i have but install updated guages..below my Steering wheel

Mike,why not buy a 12 volt gauge that looks just like your 6 volt gauge ? All of the vendors have them.

Mike, Don't know if you have an AD truck, but if you do, and you have recently painted the interior of your gauge cluster make sure you have a good ground between the back of the gauge and the cluster back case. I thought I had but ended up taking the cluster apart, sanding the inside of the case where the gauge makes contact and reassembled. Good-luck

I did by 12 volt from CCP...It better be??I am bying out of the 55-1955 book...I,m sure it is, I will have to check My records..I better look into the ground thing. (cluster)Doesnt it get grounded from the Black wire from the Ammeter? May be wrong on that,, When I mention new guage cluster (bypass the stock)...That is going to be a last resort..

NO wire on the ammeter is ever ground. If either side is wired to ground, you will have a fire.

OK..So the 2 wires into the Ammeter are hot..I was just assuming BLACK>>MEANS GROUND> I am wrong..They are real heavey Guage,,That I do Know,I am not Much of a Electrician. But I have to learn. And I have to learn fast.