Discovery about Guage Regulator

[Guest imported_Speedster]

I recently purchased a spare guage-voltage-regulator (part # 458072), that mounts behind dash of mid '50s Packards.

When I measured the resistance thru it, I found 0.ohms, so I thought it may be shorted internally.

With my normal curiosity, I desided to take the cover off and see what was inside. I had always thought is was a voltage-regulator-circuit (or Resistors), but found that it is actually a thermally activated circuit-breaker. So what Packard called a Regulator may actually be a Fuse.

If you already knew that you don't need to Tell me, unless you really want make me 'Feel Dumb'.

[Tom M]

Rick,

I feel dumb with you also it that helps you at all

[Owen_Dyneto]

I guess this unit you have isn't the resistor which is used for the gasoline and temperature gauges, because that item is a true resistor. Guess I should get out my parts book and start browsing but a bit too lazy at this moment.

[Guest imported_Speedster]

I checked the part number that was with the part and it is called a Regulator and it looks the same, other than that I've not checked further, since I previously thought the regulator was a resistor also. I suppose there could have been 2 different devices in similar cans and someone put the wrong number on this one, but not likely. (the number and name with it, were on an original Packard parts bag)

[HH56]

It is a "regulator" of sorts. The way these work is there is current flow thru the regulator and gauges and associated senders. The instruments see a current & voltage until the regulator wire heats the bimetallic strip and opens the circuit, then upon cooling, voltage again, then off and so on and on. If you look at the output with an oscilloscope there will be very crappy square wave pulses but the average voltage is considered approx 5 volts because of the constant on-off. There is a small adjustment screw that can change the amount of on time and the resultant output. Because the gauges are dependent on their bimetallic elements heating & cooling, and the slow response while that happens, the result is a smooth non perceptible movement of the needles. There can be additional resistance added in the circuit to fine tune the gauges which is what Packard did on some early 51's, I believe.

[tbirdman]

For once I know more than Speedster T-Bird's (at least 64s-66s) had a CVR mounted behind dash to supply a constant voltage to the gauges. Also the 12V regulator for the system I also believe was a switched mechanical regulator though relacement regulators are solid state.

[Guest imported_Speedster]

Thanks HH56,

Okay, it converts the constant-DC to a Pulsing-DC, therefore reducing the overall power applied. It doesn't actually reduce the voltage, but reduces the amount of time the 12.volts is applied, resulting in a lower average voltage. Got it.

Looks like it would have been easier, just as accurate and more constant to use a couple of resistors to make a voltage divider ? Since there's not much current to gauges the resistors would not need to be very large and could have been put in a can about the same size as the thermal-switch, if not smaller. And probably less heat would be generated with the resistors, since that thermal-switch gets pretty hot, I know from experience, when I stuck my hand behind dash to check something, (I burnt my Pinky on one).

Ken,

Do you know if the CVR used by Ford in the '60s was a thermal-switch type regulator or had they gone to some other circuit design by then?

[Guest Albert]

Fyi, the regulator for the 54's (6V) and the 55's(12v) are the same packard part #. a simple voltage divider will not work as well as the guages would change as the battery voltage changed,, the simplest way would be to use a LM7805 voltage regulator in it's place.

[Guest imported_Speedster]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Albert</div><div class="ubbcode-body">a simple voltage divider will not work as well as the guages would change as the battery voltage changed </div></div>

My thinking was that a Voltage-divider would probably be more stable and constant than the thermal-switch, since there is a warm up time with the switch, the contacts and bimetal-activator are going to degrade over time, and the frequency that it operates is going to be changeing as the load current changes (which will also change the average voltage level), depending on the position of the tank float potentiometer, etc. And the thermal-switch is going to be seeing the same battery voltage change that the resistors would.

And Resistor type voltage-dividers have been used in many applications to convert 12.volts to 6.volts, for complete electrical systems, with good results.

But I could be wrong.

I agree that a modern Regulator IC circuit would do a much better job, easier to calibrate and would be easy to fit into that can, and no one would ever know it had been modified by looking at it. (Not that many people are going to be crawling behind the dash to check it out) LOL