If I setup a rig as shown, can I get a fairly accurate sense if a fuel gauge will work?
My voltage supply is 3/4.5/7.5/9/12V - if needed I can use a more variable supply as well.



Can I use the same test rig for temperature gauges with a different Potentiometer range?

Does polarity to the gauge under test matter?

Thanks Sages!

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What definition of "work" do you mean? If you want to know if the gauge isn't toast, then just touch a 9-volt square battery across its terminals briefly a few times and see if the needle will move. Remember, the stock voltage limiter sends little pulses of line voltage (~13v) to the gauges to average out (crudely) to 5 volts.

If you want to know if the gauge will work accurately, that's harder; you need to factor in the resistance curves of the relevant senders.

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Too many people who were born on third base actually believe they've hit a triple.

Thanks for the ideas Dan,

Yes I want to test for working and accuracy.

I would still like to know if my proposed diagram will work.
Also any damage to the gauge under test if the polarity is swapped?

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The gauges move because a bimetal strip is heated up by a resistance wire wrapped round them. It doesn't know or care which direction the electrons are flowing through the resistance wire.

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Too many people who were born on third base actually believe they've hit a triple.

Great, good 'ol resistance things - so no semiconductors, capacitors or diodes here!

Thank you.
Greg

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try one of these for charting your gauge. After checking its made in china accuracy with a meter you can use it to simulate your sending units resistance. Just be sure to stay within the range of what the gauge expects and make sure your voltage supply is steady at the proper voltage.

https://www.amazon.com/Acxico-Resistanc ... 108&sr=8-3

I have a much much older version that looks like 50-60s vintage and I suspect was made for the military due to its markings. I can't find any pictures of mine but it comes in extremely handy on rare occasions.

Thanks for the tip, mcnoople I will have to look into those.

I believe my gauge after testing works, but it is not accurate relative to the resistances for E, 1/2, and F.

Is there a way to repair these by futzing with the bimetallic strip inside?

Corollary curiosity: Why does the Fuel gauge in my Dad's stock 1936 car go right to the fuel level when the ignition is turned on? all of my old mopars, (1962-1979) take a while to arrive at the correct fuel level. The '36 is instant.

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You would have to look at a wiring diagram of the 1936. Quick guess is that it has zero dampening on the mechanism. it could be a full 6 volts (assumed system voltage) with higher resistance values causing quicker rise times. Just a quickie on that, was it originally a 6 volt system and does it have a 12 volt charging system now? That would explain it, but I would expect big issues if that was the case.

You should see the logic circuits built into modern cars to prevent fuel slosh from causing fluctuations.


As far as calibrating the gauges, I am unsure. There are gauge rebuilding services out there. Also you could likely get all new components attached to an old face, I am sure it is pricey. For years I have looked at a company called "new vintage gauges." They have an interesting catalogs of styles and retrofit kits BUT I have no idea if they are reputable/quality/honest.....

You could probably put resistor(s) in series or parallel to the sender to change the R values when empty, 1/2, full. Never tried it, but should work.

I've always thought the Mopar 60s-70s gauges had an RC (resistor-capacitor) low-pass filter with a really slow time constant to make the response really slow so slosh didn't distract/fool you.

Lou

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Bone stock on the '36.


6v positive ground and all.

Greg

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