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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

landyacht318
Explorer
Explorer

MrWizard
Moderator
Moderator
good job
got a part number and link for the regulator replacement part ?
I can explain it to you.
But I Can Not understand it for you !

....

Connected using T-Mobile Home internet and Visible Phone service
1997 F53 Bounder 36s

westend
Explorer
Explorer
Nice work! Hope you have many more happy years with the Dodge.
'03 F-250 4x4 CC
'71 Starcraft Wanderstar -- The Cowboy/Hilton

landyacht318
Explorer
Explorer
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.

MEXICOWANDERER
Explorer
Explorer
"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?"

Salvo
Explorer
Explorer
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.

Chris_Bryant
Explorer
Explorer
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 ๐Ÿ™‚
-- Chris Bryant

MEXICOWANDERER
Explorer
Explorer
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.

wa8yxm
Explorer III
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.
Home was where I park it. but alas the.
2005 Damon Intruder 377 Alas declared a total loss
after a semi "nicked" it. Still have the radios
Kenwood TS-2000, ICOM ID-5100, ID-51A+2, ID-880 REF030C most times

landyacht318
Explorer
Explorer
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.

westend
Explorer
Explorer
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.
'03 F-250 4x4 CC
'71 Starcraft Wanderstar -- The Cowboy/Hilton

landyacht318
Explorer
Explorer
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=electro...

Could be an extremely simple solution....

MEXICOWANDERER
Explorer
Explorer
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.

landyacht318
Explorer
Explorer
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.