Voltage limiter for early A dashes

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Dartnewbie

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I assume there is no replacement for the early A's voltage limiters that are built into the gas gauge, so I am attempting to build my own. I have made power supplies for electronics before and this is a simple 5vdc supply to the gas and temp gauges. I plan on using 2 voltage regulators, one to step down to 9vdc and from there into a 5vdc to the gauges. This will reduce most of the heat generated from the regulators. The size is less than 1 inch square. It will pick up the main feed from the same wire that feeds the gauges now and connect back into the gas gas at the factory circuit board trace. If it works well enough I may make a production run and offer it as a kit and as a built unit. I am just wondering if any of you early A folks would be interested in having gauges that don't swing back and forth due to the factory limiter either going bad or just being wacky most of the time like mine is. I'll post a pic of the prototype and let you know how it works.
 
RTE Engineering already makes then...it's a plug in affair...for those that have the limiter built into the fuel gauge, you will have to remove the limiter completely before hooking up the wires to the fuel gauge...otherwise it will not work. I have done this upgrade on all my 66 Chargers...and it works great.

All parts are available at Radio Shack...all you need is the 5v transistor and the 100mf capacitor...then wire it up correctly...the 5v transistor will take voltage up to 21 volts and step it down to 5v....
 
How do you remove the limiter from the fuel gauge? I would rather remove the input to the limiter and use my own regulated circuit than possibly ruin my fuel gauge.
 
This would be good for guys like me that are not ready to remove the dash yet for restoration, but want to get their gauges working quickly.
 
Would the gas gauge still work with the old reg still in it? if not its not worth it.
 
EL5DEMON340 said:
Would the gas gauge still work with the old reg still in it? if not its not worth it.
Click to expand...

Maybe. Thing is, The resistor wires if burned in two may short out the entire circuit. If the wire isn't burned in two and the limiter is simply stuck , then decides to start working again you get waaay to much voltage thus frying the entire circuit. Bottom line... to leave the defective limiter inside the fuel gauge is not a good plan.
 
Hey Redfish. I've been reading up on switching versus linear regulators. It seems like the switching type would provide the same 5v output with much less heat and work like a solid state version of the original type. Any thoughts from you on this? I made a prototype regulator and it works on my test dash but I am getting more heat than I want from the 5v regulator when the gauge is connected. Not real hot but hotter than I like. According to what I read, the switching regulators do not dissipate the voltage by heat but actually turn off and on to maintain the output voltage. There is a 7805 drop in replacement for sale on Ebay I may try to keep the heat down. I am also curious about the speed response of the gauges using the new regulator setup. If the voltage is the same, it has to be the reduced current of 1-1.5A that causes the slower response in the gauges versus factory regulator speed. Any idea what the factory regulator current draw is?
 
That one also is using a 7805 linear regulator. I may just go ahead and buy one of the switching type and try it. They are suppose to be much more efficient and produce a whole lot less heat. Don't really like the idea of taking 14+ volts down to 5 volts in one step.
 
Why not? That's what they are built for....I have been running the limiter I built below in the Daytona, the 66 Dart, and both Chargers for more than 5 years now...no problems....yes, the initial reaction in getting the needles to move is maybe 5 seconds slower than the OE style, which puts a full 12+ volts through those little ni-chrome silk wrapped wires until the bi-metal strip breaks contact in the limiter...if it breaks contact at all, thus frying the gauges.

And yes, you have to completely remove the internal limiter from the fuel gauge...reason being is that the points on the OE limiter are in the closed position, thus creating a ground circuit....

Transistor Limiter0011.jpg
 
July 10 will be 3 years since I installed the first DeMonIVR in my daily driver
73 Valiant. That was after months of revisions and retesting.
To date I've seviced 27 rallye gauges and put 81 IVR units out there. Not one failure or complaint yet, So pardon me if I'm not interested in anything different. :)
 
Not trying to sway people one way or the other, just trying to get as much info as I can so I can make something I am happy with. The size of the heatsink on the Demon IVR is just larger than I would wish to use and shows how much heat is being dissipated. If a switching regulator would be cooler, I would prefer to go that route. I have not mentioned anything about failures, just heat. The 7805 is a great regulator, just generates more heat for my liking when putting 14+ volts to it. For the 29 cents it costs to use a 7809 in front of the 7805, I can reduce the heat by almost half.
 
I've never reinstalled the column cover in my Vailiant. Therfore I can reach inder and stick a finger to its IVR unit anytime I want. Its wram at best.
Heatsink is the key though. We looked though 1000s of them. Prototyped 5 different extrusions for testing. They sure aint created equal.
 
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