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
