Coverting a 6V VDO Fuel Gauge to 12V

[Tox56]

I am looking to by a vintage VDO Fuel Gauge for my 56 Oval...I'm trying to find one with the 56 Year stamp on it.

However, my car is running 12V electrics...is it possible to convert the Gauge to run on my 12V system as all of the gauges from that era are 6V.

If so what has to be done, is it easy?
Are there any companys doing it?
What type of sender do I need to run it???...I currently have a float style that runs on ohms and feeds my Auto Meter fuel gauge.

Or will it just run as is and I just change the bulb to a 12V?

Advice is greatly recieved as I really want to swap this Auto Meter gauge out for a period 56 VDO Gauge...the hunt is on to find a good condition one.

[Tox56]

Any ideas on the above for me anyone so I know how to proceed with this??? Advice is much appreciated!!!

[Suboval]

You can run the 6 volt gauge on 12 volts. It won't be as accurate, but it will work just fine.

I would need to see a picture of your float. 50's VDO gas gauges use floats that are 0-275 ohms.
_________________
It all works on paper.

There's two things we learn from history:
1.) History repeats itself.
2.) We don't learn from history.

[Tox56]

In terms of accuracy would it be out much then?

So did all vdo gauges up until the end of the 50's in Beetles use 0-275ohm senders?

[Suboval]

[anmilsurp]

"Striped" VDO fuel gauges don't use 10 to 180 ohm sending units. They use a filler neck sending unit that has a slightly different resistance range. A striped gauge would need to be recalibrated in order to be accurate with a 10 to 180 ohm sending unit. If it isn't recalibrated for the 10 to 180 ohm unit, it won't read empty when the tank is empty. With the tank empty it will read about 1/8 of a tank.

[Suboval]

VDO fuel gauges use a variety of different ohm floats, depending on the year and month.

To answer Tox56 initial question. If the 6 volt gauge worked on 6 volts, then it will work on 12 volts - regardless of the float/gauge combination. Depending on the combination, it will read either slightly higher or lower on 12 volts.

If you are concerned with the accuracy, then you should have the gauge/float combination calibrated to each other.


Don't forget, you still have the Reserve on the gas valve.
_________________
It all works on paper.

There's two things we learn from history:
1.) History repeats itself.
2.) We don't learn from history.

[mcelhaney14]

Look into getting an instrument voltage regulator from a 60's vintage ford mustang. For awhile ford was using 6 volt instruments in 12 volt cars and used this regulator.
William

[Tox56]

Is the best thing maybe to buy the gauge and then go for the corresponding sender that would match it then?

I was looking at maybe opting for this gauge:

http://www.thesamba.com/vw/classifieds/detail.php?id=1269306

[Andy Sparks]

can't you use a voltage drop resister? will drop the 12v to 6v, just wire the complete circuit through that.

[Tox56]

I want to avoid using additional components like voltage reducers...although functional the look of stock wiring is compromised.

[Tox56]

[jwr!]

Hi,
I found this old discussion on fuel gauges and saw that Suboval was testing the gauge to determine its ohm range?

I have s basic idea of how to test a random SENDER on a multimeter so it shows ohm range, but how do you test the FUEL GAUGE itself when you just have a random one out of a parts bin that you want to use in your car but no idea of the sender required for it? Would like to know how to test the gauge or where to finder a marker on/in the gauge that would indicate the ohm range for appropriate sender selection?

Many thanks for your help!
Regards,
Jason

[j-dub]

Jason,
In the picture above for testing the gauges Suboval was using a potentiometer which is an adjustable resistor to find out what what resistance range it requires for the gauge to sweep from full to empty. You can see in his notes that each gauge varied a bit but they trended the same.

The gas gauge is based on a simple voltage divider circuit, there is a fixed resistance and a variable resistance, sending unit. The needle indicated the proportion of each.

Jeremy
_________________
1957 Oval rag
"POLICE STATION TOILET STOLEN ... Cops have nothing to go on."

[Suboval]

[jwr!]

Thanks Jeremy..
Thanks Kurt...

Much appreciated for the response. I thought/hoped maybe that there was something additional used in testing, that would remove the back and forth multimeter measurement process with the potentiometer.

I have seen 'Ohm Wheels' that have all of the ohm ranges marked so you could 'dial in' and record, but they are rated only up to a few watts when in actual fact I imagine that one would required one rated up to about 500ohms and 100 watts to cover the range of 6v & 12v fuel gauges?

My electrical knowledge is limited and is took some research to just get to this stage! Ha!
Thanks again!
Jason

[jwr!]

Hi again guys...
I'm not great with electronics, wondering if you can help?
I tried to test a bunch of early VW 6v fuel gauges using a 500 ohm potentiometer but they all read the same.

Using a small 6v plug in wall transformer...
Potentiometer is connected in line with the +ve line of the 6v feed.
This connects thru to +ve terminal on the fuel gauge.
-ve from the 6v power feed connects thru to the -ve terminal on the fuel gauge
At 0 ohms the gauge reads on full & then I turn to 500 ohms & the gauge drops to about 3/4 of a tank. I assume that I am just not doing something right?

I imagined that the fuel gauge indicator should change incrementally with the rotation of the potentiometer? Can you shed some light on what I a screwing up?

Many thanks!
Jason

[j-dub]

From another thread:

[jwr!]

Thanks j-dub, but no this does not assist.

I am not looking for a schematic on how to connect a gauge in a vehicle. I am trying to problem solve the testing of the ohm range that does not seem to be giving correct readings.

I was hoping that jury could provide a similar picture of his test and some notes on quite specifically what goe where & how he tests. My method seems to be flawed...

[j-dub]

Look again at the diagram that Kurt provided.

Based on your previous post you were using the potentiometer on the 6 volt feed, that is incorrect.

The potentiometer is supposed to replace the sender in the diagram.

Is that clear? All the sender is at the end of the day is a potentiometer, variable resistor.