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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
  • Well, I opened up the cluster, removed the limiter, and there, in the same place as the photo in the OP, is a little adjustment knob.

    I could have easily moved this during cleaning. I don't have an analog voltmeter so I cannot adjust it properly, and I do not know what it was actually set at before. Also with its age, perhaps it is foolish to put this back into use after adjusting it.

    It strikes me that I have the opportunity to dial in my Fuel gauge so half a tank actually indicates half a tank, instead of indicating 5/8ths a tank. This unit appears to fit this bill nicely. I could mount it remotely to easily adjust the set screw.
    DROK 3a buck converter

    While the temp gauges and OP gauges will have a 'new' normal range, I have a mechanical OP gauge plumbed in, and merely tolerate the Stock gauge. The Oil light is still operational as well.

    I decided to practice soldering with my newish 100/140 watt weller gun. The primitive circuit board has a bunch of pins with a mechanical connection. They all now have a nice base of solder meeting the traces.

    Same with the voltage limiter attachment points.

    Here's to rock steady gauges in my future.

    There is a capacitor on the CB traces between (+) and (-)
    .47M250 V U

    The V is actually a triangle.
  • wa8yxm's avatar
    wa8yxm
    Explorer III
    I actually know how those work,, They are vibrators basically, or choppers

    You have, basically, a relay in side the box. And possibly a small condenser.

    The relay is normally closed, that is the HOT (Battery) wire is connected to the output (METERS) wire. and to the condenser.

    As the voltage rises the magnet coil pulls the relay open, Now the condenser is powering thigns,, This does not go on long, but the coil now drops the armature (since the voltage, and thus the current, is falling) and it returns to connected state, then the voltage rises and the magnet pulls the armature in again, opening the relay and.. This happens several times a second.

    Thus it is a chopper.. chopping the incoming voltage to lower it.
  • It chops, others buzz, and still others, pout and stay out of the circuit (breakers).

    I've not yet met the instrument cluster regulator that was accurate.

    At 0F your gas tank will read extra full while at 105F the needle may not reach "F".

    In college working as a line mechanic in a Dodge agency I made good money with Q-tips and fine grade valve grinding compound shining up imstument circuit board contacts for these regulators. A splotch of Vaseline petroleum jelly. Never a grumble or comeback. Service manager was madder than hell because I was charging Dodge the full 1.1 hours the crooks allowed for instrument circuit board R&R. Then the parts manager informed me the dealership was charging Dodge for my phantom circuit boards.

    With the buckers on eBay I wouldn't spend two cents on a replacement instrument volt reg today.
  • Didn't they use this method for regulation from alternators (or probably generators)? Also, for old inverters?

    Wonder what of today's technology people will look at as stone age :)
  • That part looks like a 5V regulator. My son's '68 Dodge Charger has similar part. The newer ones are now switching regulators, the old are linear.
  • "Danger Will Robinson! Danger!

    2115 will be so ridiculously advanced when somone mentions a tablet it'll have them rolling on the ground.

    "What! No holograms?"
  • My 7 dollar solid state solution is now in place, and my gauges no longer swing wildly for no discernable reason.





    I mounted it so I can still fairly easily access the adjustment screw. It is at 5.12 volts now, and the gauges read a smidge lower than what was normal, on level ground with steady battery voltage, with no radio interference, or any other gauge swinging factors.

    Red incandescent bulbs found their way into the cluster, and the green turn signal indicator and the blue high beam indicator got colored LEDS which are much brighter and richer in color than before. I went Incandescent on the background lighting as LEDS do not properly work with the stock dimmer, and I am not wiring up a PWM dimmer just to save ~1.25 amps that the 194s consume.
  • Nice work! Hope you have many more happy years with the Dodge.
  • good job
    got a part number and link for the regulator replacement part ?

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