If you've been following my work on the 12v to 6v adapter (well, actually any adapter I make will fortunately for the owner be adjustable), you know a decent amount of progress has been made and much of this work has centered around the 6v gas gauge since I suspect it will be the primary use for most people...and I admit I'm willing to overlook some things, but a wonky gas gauge isn't one of them. You may also recall I said early on I knew the 6v gas gauge would work on 12v, and I added I didn't know what the long-term consequences or effects of using it with 12v might be. Now I do know and in a moment I'll share with you. Electromagnetism is what makes the gas gauge work and current is important if you're trying to create electromagnetic fields. And I wish it was just that simple, but it isn't. Voltage drives current, so to say there is no difference between 6v and 12v as far as your gas gauge goes isn't correct. I also mentioned when used on 12v, the needle on the 6v gauge moves faster or with more authority. With 12v, there is more current and more magnetism and it does matter.
What I have learned over the past 10 days is this: If you have been using your gas gauge on 12v, it is likely it won't work accurately on 6v any longer. I believe the increased magnetic field brought about by 2 times the proper voltage has permanently increased the magnetic part of the gas gauge shown by the green pointer in the image below, and that will make a difference. What I discovered (unexpectedly) is the Vol-Ta-Drop I have been using for 40 years at some time in the past malfunctioned and was outputting 12v and not 6v on the side of it I was using for the gas gauge. When did this occur? I can't unscramble that egg, but I suspect exposing your gauge to 12v might start to change things quickly, because we're dealing with a very small piece of magnetized metal there. And what I do know for certain is that 6v and up to 5 amps of current (which is much more than enough for this gauge) will no longer make my gauge work correctly. It will not advance to full and I suspect the reading throughout the entire scale has become flawed at 6v.
This all came clear when I completed one voltage adapter using a sample 5 amp chip Texas Instruments sent me. I filled the tank completely, connected the adapter (adjusted for 6v) and was perplexed to find the gauge would only register a bit less than 7/8 full. With 12v it jumps crisply to the full mark. Then I used one of the 1.8 amp adapter prototypes I made and set it for 6v. Same exact thing and I should add in both cases the needle moved more lazily at lower voltage. Finally I used one of the 1.5 amp adapters set for 6v and the results were identical...sluggish movement and would not register full.
So then all three prototypes were installed at different times and each was adjusted with the ignition on so I would have no idea what the output voltage was that made the gauge work properly. They were adjusted so that the needle traveled up at the speed I thought was appropriate and travelled up to the proper "full" spot. And then the voltage output for all 3 was checked on my work table. The result? It takes 8.4~8.5 volts for my gauge to work properly now. Anything below this will cause the problems previously mentioned. I should mention 7.2v~7.5v (which as Jerry has pointed out is what the 6v generator will output) will not make that gauge work now. When I discovered this, I took the high amp regulator, adjusted it for 7.5v and the result was virtually indistinguishable from 6v. At 12v the gauge naturally still works, but my question is: Will the extra emf generated by 12v ultimately mean it no longer works as it should? After all, I have no idea how long the problem with the Vol-Ta-Drop has existed. More to follow on this in time.
~ Jon 1952 1/2 ton with 1959 235 | T5 with 3.07 rear end
Jon I shamelessly borrowed your picture. Good write-up but I'm a bit slow. Are you saying the needle is bent? A sudden higher voltage, than the scale can take, will do it.
"Adding CFM to a truck will only help at engine speeds you don't want to use." "I found there was nothing to gain beyond 400 CFM."
Hi...sorry I've been up in Arkansas for a funeral. Actually I'm saying I believe that piece marked by the green arrow has become over-magnetized by too much voltage/current. Which can happen. A strong EMF can produce a magnet or it can raise the strength of an existing magnet if the existing magnet is oriented correctly. That piece is supposed to sit as you see it there, but a little further over to the right. The magnetic piece in question is sort of hourglass shaped and the needle comes off it at that angle. It isn't the sudden higher voltage causing the problem. 12v is 2x the 6v to 7.5v the gauge was designed to operate with. And I believe the reason the gauge (which is in otherwise good nick) won't work with either 6v or 7.5v is because that hourglass shaped piece of metal (which was always magnetized) now has been overmagnetized. When 12v is applied to that gauge, the needle will travel right to the F mark crisply. Remove 12v and apply 6v or 7.5v or even 7.75v and the needle will not travel up to the F mark at all. But if you apply 8.4v or 8.5v, then the needle works correctly again.
~ Jon 1952 1/2 ton with 1959 235 | T5 with 3.07 rear end
Hey John, a little off subject but if you don't mind,,,, what do you think of the resistor (round thing with a wire sticking out of both ends) some guy sells to reduce voltage to the gauge? Seems to work for me but I have to admit I do not remember ever putting a meter on it to check the voltage.
Back before there was integrated-circuit voltage-regulators the original and traditional way was to use a resistor. The most common was called Volt-A-Drop. Basically a wire wound resistor protected by a ceramic block. There were versions for a heater and separately a radio but each had an accessories terminal. They worked good enough but their wire wound resistors consume power and generate heat. You didn't want to use them long without running the engine. It would drain your battery. The fuel gauge and fuel level sensor do not consume as much power so yes you can use a single resistor. It is the most basic way to do the voltage drop but it is also the worst for voltage regulation.
"Adding CFM to a truck will only help at engine speeds you don't want to use." "I found there was nothing to gain beyond 400 CFM."
It might work ok for the gas gauge. As mentioned, the gas gauges will work on 12v. The thing about that is nobody knows the long term effect. I understand some people have used their gauges on 12v for many years, but for how many hours? Based on what I discovered, I'm almost certain the little metal piece will in time become so over-magnetized it will never again work on anything but 12v. Which might be ok. But the flip side to that is the magnetic coils may in time be affected, also. It will take a long time, but the effect will be irreversible.
The real key with voltage reduction is to think of it as voltage destruction. And when you destroy electricity, the unwanted/unneeded portion becomes heat. With the resistor, often the heat ranges from objectionable to dangerous. But not with the gas gauge. It doesn't use enough juice to be a problem. Personally I don't like this method, however that's probably just me. Soon...very soon...I'll be finished testing a handy adjustable voltage reducer I've made. More to follow...
~ Jon 1952 1/2 ton with 1959 235 | T5 with 3.07 rear end
The Vol-Ta-Drop was my favorite for years, but about a month ago I discovered mine had (at some point in time) failed. And the failure in my case meant it shorted and was providing a pure 12v output.
~ Jon 1952 1/2 ton with 1959 235 | T5 with 3.07 rear end
