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landyacht318's avatar
landyacht318
Explorer
Mar 03, 2015

How does this elderly Voltage Limiter work?

This is a Voltage limiter, for my Fuel, coolant temp, and oil pressure gauges in my '89 Dodge van.



It plugs into my gauge cluster and is not extremely simple to access.

My Factory service manual says this limiter sends out" AN EFFECTIVE 5 VOLTS" to these gauges

In another part of the manual, it says when testing this limiter, if the voltages fluctuate, then it is operating properly.

My voltmeter is jumping all around when attached to the output and ground tabs. The input is steady battery voltage.

Recently, because of high amounts of stubborn oxidation on the glass fuse holders, I decided to open up the dash and get some Caig Deoxit on the connectors and make them gleam like oiled chrome instead of white 320 grit sandpaper. The Fuel and temp gauges, in the past have swung in unison fairly wildly, So I really wanted to get to this voltage limiter and clean the contacts.

Anyway I did so, and now all the gauges read high. Much higher than normal, higher than they seldomly swung in unison before.

They say this can be a faulty voltage limiter, or a bad ground. It is not a bad ground. And I fear my aggressively cleaning the tangs of this limiter with a wire brush on a dremel, screwed up the internals.

It is 35$ for a new one which seems a bit ridiculous. The Pic above shows a few tangs that one could pry up and access the internals. The one in my dash cluster has a full perimeter seal making access to internals much more difficult.

So how do these things work?

Why is it not a steady 5 volt output but instead jumps all over the place?

How could my cleaning of it with a dremel and soft wire wheel, and Caig DeOxit d5 cause it to read so differently and raise all my gauges?

(The temp gauge now reads 25% higher than ever before, well outside the normal zone. The engine is running at its normal temps.)

If I were to give the dash gauges a steady 5 volts from a device like this, will they operate in their correct range?

http://www.amazon.com/LM2596-Voltage-Regulator-Voltmeter-Converter/dp/B00GN1SU0C
  • The cause of the difference after cleaning may be that a bit of oxidation or dirt has fallen into the adjustment mechanism and changed the resistance. Being squeaky cheap as I am, I'd put some compressed air to it and fiddle with the adjustment to see if I could revive it to pre-cleaning attributes.

    Then again, a 12v->5V regulator is only a couple of bucks from E Bay.
  • Thanks for all the input. Others have already blazed this trail before:

    http://www.allpar.com/history/mopar/electrical2.html

    I'll just have to follow.

    35$, my Donkey.

    That top photo in the OP, shows a little adjustment knob. I did not notice this on mine, but I imagine if it is there, I bumped/ turned it with a Q tip.

    Frying the gauges is not something I care to do, so the solid state option will be the path pursued

    Hmmm. 5 volts DC

    Same as a USB plug output.

    All sorts of options to consider:

    http://www.amazon.com/KEEDOX%C2%AE-Converter-Power-Supply-Module/dp/B00A71CMDU/ref=sr_1_12?s=electronics&ie=UTF8&qid=1425357711&sr=1-12&keywords=DC-DC+Buck+Converter#Ask

    Could be an extremely simple solution....
  • It would be tempting to use an LM7805 and connect a 1-amp silicon diode in series with the center (ground) pin to yield 5.7 volts. But take care with current. 1.5 amperes max. The metal TO3 case reg might be worth considering - twice the current capacity. Voltage buckers are soooo cheap...

    "How cheap? How cheap? Tell us! Tell us!"

    Around four dollars on eBay. Adjustable voltage. Rock solid dependability.
  • Thanks.

    I found this link online which shows some internals, and modern(2002) solutions

    http://www.chargersourceguide.com/voltagelimiter.html

    I'll not spend 35$+ for this ancient technology when better modern options exist for a fraction of the price.

    I'm guessing some DeOxit d5 got inside the unit and affected the resistance of the unit.

    I'm only going to open the old one once I have a working solution in place. I fear letting the smoke out of the gauges, and am just going to unplug the limiter now until the new product arrives.
  • I say give it a try. It requires very little current so a LM7805 in a to220 package should work - or it kinda did for me.
    It would only cost $2 to try.
  • Well the factory service manual says 5 volts. The Standard motor parts replacement says 6 volts. I can't measure an average voltage with my tools but I suspect it is now significantly higher than before the cleaning.

    Opening this original up will not be so easy.

    I'm just having a hard time considering spending 35$ when a steady 5 volts, or 6 volts, or 5.547v can be applied with a 5$ piece of modern electronics.

    I am 5 3/8" nuts from accessing it right now.
  • landyacht318 wrote:
    Thanks for quick response. So I imagine the LM 2596 supplying a steady 5 volts would also operate the gauges properly?

    I have one of those on a computer fan whose hub gets too hot at Absorption voltages and it holds a rock steady voltage no matter the input voltage, and has been plugged in for 6 months now, continuously.

    Any theories as to why my cleaning of this stock unit caused the range to change and raise my gauges?


    I don't know what the Dodge CVR output is exactly but if it's like the old Ford part then it needs to be about 6 Volts. If you use a 5V regulator then everything reads way too low (I've tried it!).

    Don't know why cleaning it changed things - weird.
  • Thanks for quick response. So I imagine the LM 2596 supplying a steady 5 volts would also operate the gauges properly?

    I have one of those on a computer fan whose hub gets too hot at Absorption voltages and it holds a rock steady voltage no matter the input voltage, and has been plugged in for 6 months now, continuously.

    Any theories as to why my cleaning of this stock unit caused the range to change and raise my gauges?
  • That's a classic!
    It has a bi-metal piece of metal in it that heats up and breaks contact, then cools and makes contact again. It repeats this cycle several times a second and keeps the average voltage at about 6 volts or so (that's why it's so erratic). When they fail they stick closed and send full battery voltage to the gauges which often ruins them.
    You can go to NAPA and get a modern electronic version that is longer lasting and safer.

    In the days of slow analog meters, you could measure it and get a fairly steady reading. But todays DVM's are way too fast and accurate to be fooled by that.

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