12 volt to 6 volt adapter for fuel gauge

[The Rabid Whippet]

I just talked to an electrical engineer and he was saying that the 1936 Fuel Gauge has to have a non fluctuating 5 volt regulator to be accurate. He was telling me he uses a 3 pin regulator with some diodes to keep it at 5 volts even with the 12 volts fluctuating. Soooooooo I got on line and checked out 12 to 5 volt regulaters and didn't come up with too much. But while I was doing it, I thought about my phone charging on the 5 volt USB from my computer. I then went to my old junk cell phone adapters and found one that I cut the end off and exposed the 2 wires. I plugged it in and tested the voltage. 5.38 volts running or not. So I stripped the board out of it and will tie it into the 12 volt line and through it to the fuel gauge. Think it will work? And if it does, heres a cool tip for everyone to use to convert your old 6 volt gauge to work cheap as everyone has some sort of old cigarette lighter adapter to charge their old phone that they no longer have.

[tommy]

I got a runtz from Ebay because it was the cheapest. It came with directions and was simple to hook up. 1 for the 12 Vs 1 for a ground and one to feed the 6V gauge.



It works perfectly so that I can run a 6V big logo SW gauge on my 34 P/U.

[themoose]

This regulator should work.Voltage regulators take a range of DC voltage and convert it to a constant voltage. For example, this regulator, a 7805 regulator, takes a range of 8 - 15 volts DC input and converts it to a constant 5-volt output.
http://www.parts-express.com/pe/show...artnumber=7805

[squirrel]

go to radio shack, local and affordable

http://www.radioshack.com/product/in...ductId=2062599

[d2_willys]

Originally Posted by The Rabid Whippet

I just talked to an electrical engineer and he was saying that the 1936 Fuel Gauge has to have a non fluctuating 5 volt regulator to be accurate. He was telling me he uses a 3 pin regulator with some diodes to keep it at 5 volts even with the 12 volts fluctuating. Soooooooo I got on line and checked out 12 to 5 volt regulaters and didn't come up with too much. But while I was doing it, I thought about my phone charging on the 5 volt USB from my computer. I then went to my old junk cell phone adapters and found one that I cut the end off and exposed the 2 wires. I plugged it in and tested the voltage. 5.38 volts running or not. So I stripped the board out of it and will tie it into the 12 volt line and through it to the fuel gauge. Think it will work? And if it does, heres a cool tip for everyone to use to convert your old 6 volt gauge to work cheap as everyone has some sort of old cigarette lighter adapter to charge their old phone that they no longer have.

I doubt this will work real well, as the charger is just what it says it it: A CHARGER, which only puts out so many milliamps. Your gauge, when the sender is at ground side draws more current than those chargers can put out. Even with the sender on the 90 ohm side, you are looking at 133ma, which means this charger is not going to work.

The 3 terminal regulators are ok, but you have to remember that you are pulling 133ma (at 90 ohm side of sender, more at other end), so 6 x .133 = .8 watts is what the regulator will dissapate in power.. If you use one, make sure the tab is mounted to a good grounded piece of metal to sink some of the heat.

[squirrel]

usb chargers are rated for one amp....?????

Also there is quite a bit of resistance in the gage itself, did you take that into account?

[Rocky]

I've always used the original voltage limiters on the back of 56-64 ford insturment clusters to feed any 6 volt gages....always worked for me. Last one I bought new at Ford was about 18 bucks but there are always a few on any 56-64 ford or International pickups in the junk yard..

[squirrel]

The thermal Ford regulators might not work so well on a GM magnetic gage...

[Truckedup]

Originally Posted by squirrel

The thermal Ford regulators might not work so well on a GM magnetic gage...

Maybe..I do know from messing with GM 6 volt fuel gauges that around 7 volts steady is required for accuracy

[F&J]

Some of those IC regs come in different milliamp ratings. Look on ebay for surplus leftovers from manufacturing companies special projects.

I found some at 3.6 amp that I ran a '65 365 Porsche tach with. Most ran around 300 to 500 M/A at that time, but you may find others

[Rocky]

Originally Posted by squirrel

The thermal Ford regulators might not work so well on a GM magnetic gage...

60 ford pickup limiter used on my old 48 and 41 Pontiac original gauges worked flawlessly.

[jack orchard]

is there any reason for running 7805 regulators (that put out 5 volts) instead of 7806 regulators that put out 6 volts? just curious...jack

P.S. 10 7806 1.5 amp regulators for $4.50 w/free shipping on Ebay

[dirt t]

Go to Tech arkives search for 1.98 6 Volt gage.

[F&J]

Originally Posted by jack orchard

is there any reason for running 7805 regulators (that put out 5 volts) instead of 7806 regulators that put out 6 volts? just curious...jack

The 5 volt ones were all we could get 30 years ago at Radio Shack. And then we had to add a Zener diode to one leg to bump it to 6v output. There were no 6v available then, to retail users.....

Modern times,... and now you can get these in different voltages, both input and output, as well as milliamp capacities.

[jack orchard]

Thanks, F&J. I figgered there was a reason. I just didn't know what it was. Now i do...jack

[The Rabid Whippet]

I just picked up a 7805 after I read the first couple posts. The guy that I talked to came highly rated from the Ford Barn as he rebuilds factory gauges and he actually converts the tube gauges to LED but look totally stock when off. Anyway he seemed very knowlegable and told me that the term for people like me that they use between themselves is I'm open loop. I know what that is and it sort of offended me as I figure alot of stuff out that is out of the box and works like my tech on Hemi water pumps modified from on the shelf stuff and a ton of other things I have just figured out. There are lots of terms that I have heard for engineers also but we won't go there. As far as the charger, I figured that the wires are very thin but so is the wire that is in the gauge. But I also do research and this is what I do when I am not sure on stuff. Like right now being on the forum and listening and learning from others that have already done their reseach and development.
The person I called said that the 5 volt is a better reading and is better calibrated to the factory 1936 Ford gauge. I'm not sure about this as didn't the 6 volt battery actually charge at like 6-7 volts and this would be the voltage into the gauge? Just like the 12 volt systems actually charge at 13.5-14.4 not 12 volts. I also just got a new sender from Bob Drake that is 10-70 ohms which this person recommended and had his 85 year old brain just spit out the BD part number. I'd like to hear more about why the 7805 is used and not the 7806 now from the ones that actually know and not just what people guess is the reason. Why did this guy say 5 volts is what the factory calibration is? Or does it just work better with the sender? I will have the sender by Wednesday and have it installed by Friday. I hope it will be accurate. If I hear that the 7806 is the one needed with the reason why, I will exchange the 7805 tomorrow.

[Hnstray]

Great thread! Thanks to all................

Ray

[d2_willys]

Originally Posted by The Rabid Whippet

I just picked up a 7805 after I read the first couple posts. The guy that I talked to came highly rated from the Ford Barn as he rebuilds factory gauges and he actually converts the tube gauges to LED but look totally stock when off. Anyway he seemed very knowlegable and told me that the term for people like me that they use between themselves is I'm open loop. I know what that is and it sort of offended me as I figure alot of stuff out that is out of the box and works like my tech on Hemi water pumps modified from on the shelf stuff and a ton of other things I have just figured out. There are lots of terms that I have heard for engineers also but we won't go there. As far as the charger, I figured that the wires are very thin but so is the wire that is in the gauge. But I also do research and this is what I do when I am not sure on stuff. Like right now being on the forum and listening and learning from others that have already done their reseach and development.
The person I called said that the 5 volt is a better reading and is better calibrated to the factory 1936 Ford gauge. I'm not sure about this as didn't the 6 volt battery actually charge at like 6-7 volts and this would be the voltage into the gauge? Just like the 12 volt systems actually charge at 13.5-14.4 not 12 volts. I also just got a new sender from Bob Drake that is 10-70 ohms which this person recommended and had his 85 year old brain just spit out the BD part number. I'd like to hear more about why the 7805 is used and not the 7806 now from the ones that actually know and not just what people guess is the reason. Why did this guy say 5 volts is what the factory calibration is? Or does it just work better with the sender? I will have the sender by Wednesday and have it installed by Friday. I hope it will be accurate. If I hear that the 7806 is the one needed with the reason why, I will exchange the 7805 tomorrow.

Years ago Ford used a device called an IVR, which is short for instrument voltage regulator. What it did was to provide an averaged 5 volts for the gauges. This was done by means of a bi-metal strip opening and closing the circuit, which provided the averaged 5 volts. Now your 1936 might be different, but it might be close enough for the gauge accuracy.

As far as using the USB phone chargers, it might be worthwhile to know that these chargers could be (and probably are) switch mode type regulators. Switch mode regulators rely on pulse width modulation to provide the output voltage. In general they are very efficient, but one must remember that they run at a switching frequency. If the switching frequency can provide a strong enough harmonic in the audible range, the gauges might send out high pitch frequencies that you can hear. The probability of this is very low, but still possible. The USB charger for my phone does put out 5.1 volts, but only handles .7 amps. If this is used for gas, oil, and temp gauges, the chances are that it will not be powerful enough.

My recommendation is to use a 7805 regulator and mount it to a good clean ground metal. Don't forget to put decoupling and bypass capacitors on the input and output.

Another simple possibility would be to install a 6.1 volt 5 watt zener diode from 12 volt ignition power to gauge hot sides. The banded side goes to the ignition power. You can use one for each switch as they are small in size and do not need heat sinking.

[The Rabid Whippet]

decoupling and bypass capacitors on the input and output.
What would these do and are they necessary? All I want is my fuel gauge to work. I don't need the other gauges. I have accessory gauges below the dash.

[d2_willys]

Originally Posted by The Rabid Whippet

decoupling and bypass capacitors on the input and output.
What would these do and are they necessary? All I want is my fuel gauge to work. I don't need the other gauges. I have accessory gauges below the dash.

Although the datasheet says it is not necessary to decouple and bypass the input and output, it is a good idea and is very reasonable in cost. Simply solder a .1uf capacitor across pin 1 to pin 2, then solder another .1uf capacitor from pin 2 to pin 3.

The output bypass capacitor will smooth out any transients, the input cap will drown out noise such as regulator, generator, or alternator noise.