Fuel gauge 12v - 6v

1941 - 1945, MB, GPW Technical questions and discussions, regarding anything related to the WWII jeep.
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Lukasdelemetrio
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Fuel gauge 12v - 6v

Post by Lukasdelemetrio » Sat Mar 03, 2018 7:42 am

I apologise if this has been covered before but I can’t seem to find an answer on here.

Recently had my original long needle fuel gauge restored. Problem I’m having is my jeep is 12v and the gauge has been restored to its original.

Is this what I’m looking for?

Image

And how would that be wired up? I thought just earth the negatives on input and output to the jeep but I’ve been told by an auto parts dealer that this wouldn’t work.

I’m no electrician.

Thanks for your help

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Re: Fuel gauge 12v - 6v

Post by Wolfman » Sat Mar 03, 2018 7:59 am

That would work, But a whole lot of over kill just to get the fuel gauge to work.
If you plan to use this unit to convert the entire electrical system, 18watts and 3 amp load won't not be enough.
Have you tried the gauge to see what it reads now ??
I am thinking if there is a problem, the gauge will read too high.
A resistor in the wire from the gauge to the tank unit would solve the problem.
Don't have an exact value. You may have to experiment a little to get the resistance correct. There is little current flow to the gauge so the resistor would not have to be the big, white, ceremic resistor like used with ignition coils. Just a small resistor like used in radios or TVs will work.
Mike Wolford
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Lukasdelemetrio
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Re: Fuel gauge 12v - 6v

Post by Lukasdelemetrio » Sat Mar 03, 2018 8:19 am

Hi mike,

Ok so the live into the fuel gauge being 12v wouldn’t melt anything? Like blowing a bulb?

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Re: Fuel gauge 12v - 6v

Post by Lukasdelemetrio » Sat Mar 03, 2018 8:22 am

*also I didn’t plan on converting the whole system just want to step it down before the gauge as to not damage the gauge? Or am i being stupid?

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Sean Collins
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Re: Fuel gauge 12v - 6v

Post by Sean Collins » Sat Mar 03, 2018 9:39 am

Use a 24 ohm, 5%, 5 watt resistor.

Put it inline between ignition switch and gauge.
 


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Re: Fuel gauge 12v - 6v

Post by Lukasdelemetrio » Sat Mar 03, 2018 9:58 am

Thanks Sean will do!

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Re: Fuel gauge 12v - 6v

Post by Wolfman » Sun Mar 04, 2018 6:53 am

Nothing stupid about asking questions.
The converter is a whole lot of over kill just get the fuel gauge to read correctly.
Two ways to attack the problem.
What Sean said. Put the resistor in the B+ side of the fuel gauge to lower the voltage at the gauge.
Or
Put a resitor between the gauge and the sending unit to adjust the resistence at the sending unit for the higher voltage going through the gauge.
Raise the bridge or lower the water scenerio.
Since Sean has given a resistance value for his way. I would do that one.
Have you tried checking to see what the gauge reads at 12 volts without any alterations ??
The reading may be acceptable the way it is.
Mike Wolford
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Re: Fuel gauge 12v - 6v

Post by Lukasdelemetrio » Sun Mar 04, 2018 9:40 am

Hi mike,

Thanks, this is my first jeep and I’m still learning.

I haven’t tried hooking it up yet as I thought it would maybe just fry the gauge like running 6v bulbs on a 12v jeep (did that a few times before I realised).

I’ve ordered some resistors so I’ll give that a go.

Thanks for your help

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Sean Collins
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Re: Fuel gauge 12v - 6v

Post by Sean Collins » Mon Mar 05, 2018 7:59 am

Lukasdelemetrio wrote:
Sun Mar 04, 2018 9:40 am
...I haven’t tried hooking it up yet as I thought it would maybe just fry the gauge like running 6v bulbs on a 12v jeep.
It will work on 12v (without instant burnout like a bulb), but the gauge internals get 4 TIMES HOTTER than on 6v. Most will continue to work on 12v, but some eventually fail due to excess heat.

The feed line resistor keeps the voltage between 6-8v, and gauge heat w/in 6v nominal temperatures, and the resistor dissipates the remaining heat (about same as the gauge system @ 2.5 watts).
 

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Re: Fuel gauge 12v - 6v

Post by Wolfman » Mon Mar 05, 2018 8:29 am

I have been assuming ( there is that word ) we are dealing with an unbalanced fuel gauge. I am wrong. Sorry.
If you go down to the general discussion section, there is another post on fuel gauges.
Marty has enlightened me that we are dealing with a balanced gauge. Not unbalanced.
Changes everything.
First of all, do as Sean said. Put the resistor he suggested in the power wire into the gauge, from the ignition switch.
But this still may not solve your problem.
The second coil in the balanced gauge and the sending unit still need to match. I went into that in the other post.
If you are using an original gauge with an after market sending unit, the resistance in the sending unit may still not match what the gauge needs to work properly.
Some adjustment in the resistance to the gauge may be required.
Mike Wolford
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Re: Fuel gauge 12v - 6v

Post by rocgpw » Wed Mar 07, 2018 5:37 pm

Good day, Lucas.
My jeep has been converted to 12 volt. The fuel gauge is original and has had a 6 volt voltage regulator included in its circuit between the circuit-breaker and the gauge. It is called a 7806 regulator and reduces the 12 volts to provide a stable 6 volt D.C. supply for the gauge to operate properly. Using a resistor instead may supply a varying voltage to the fuel gauge, depending on what the charging system is doing at the time whereas the regulator will be consistent in its 6 volt supply Connection details of the regulator are easily found on the internet otherwise PM me.
Regards, Richard.

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Re: Fuel gauge 12v - 6v

Post by Lukasdelemetrio » Thu Mar 15, 2018 3:37 am

Hi Richard,

Thanks, I will look into it!

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