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How does this elderly Voltage Limiter work?

landyacht318
Explorer
Explorer
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
20 REPLIES 20

ScottG
Nomad
Nomad
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.

landyacht318
Explorer
Explorer
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.

time2roll
Nomad
Nomad

ScottG
Nomad
Nomad
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.

landyacht318
Explorer
Explorer
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?

ScottG
Nomad
Nomad
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.