Fuel gauge in my 79 Volare is reading 3/4 when full and temperature gauge is barely moving showing low engine temp.
Installed a new fuel sending unit but the gauge still reads 3/4 when full.(the old/original unit is good, ha!)
I checked the voltage limiter output and it osclilates between 9 and 10-11 volts, not the 5V the volmeter is supposed to see.
Is this higher voltage output cause for the pointers not to show the correct readings, i.e.: 3/4 when tank is full and low temp when actual temp is 185°F?
Thanks for your inputs

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Rafa

Hecho en México

Your voltmeter will not show 5v because the oscillation is so slow, maybe once a second if that. If you wanted to see 5v on your meter the oscillation would have to be several hundred times a second probably.

It should go all the way down to zero, then back up to battery voltage. Hook up a 12v lightbulb to the output of the meter, and see if it completely dimms when turns off. If not, then the limiter would need replacing. But while you are at it and have the dash apart you may as well convert to the solid state 7805 regulator as per the articles availbile on this site and others.

Thanks Pierre. I knew you were the one to come to my rescue.
Yeah, I have already opened a case of one of the limiters -have 5-, downloaded the article on converting it to solid state, went to Radio Shack today but they do not have the 7805 regulator listed for all of México. (aahhhh! those mexican radio shacks )
I did find www.steren.com and they do have both the reg and the capacitor.
Now on capacitors, the PCB has an original capacitor installed between ground and the 12V input, but I thing it's not the correct cap for this application. Its id'ed as .47K250P. So for the price of the new one I will remove this one and install the one suggested in the articles.
I do not know much about electronic components -nada- but I'm very good at soldering and following instructions, so with a good set of instructions I'm sure I will succeed.

Is there anything else you may want to add?

Thanks again. Will post when I'm done.

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Rafa

Hecho en México

Hey I'm surprised they even have Radioshacks in Mexico

I wouldn't worry about the value of the cap too much, as converting to solid state makes them pretty much unnecesary, adding them only steadies out the readings of the gauges so they don't bounce around too much with fluctuations in battery voltage. 1uf, 10uf, 50uf etc on the output is fine. The one on the 12v input isn't necessary at all but if you want to put one there by all means.....

Only critical thing is to heatsink it well as it will dissipate a good ammount of heat. Use some thermal grease on back of the regulator if you have any (also a ratshack item). Remember the tab on the back of the solid state regulator is equivalent to the center leg, or ground.

So am I, but they don´t stock many of the "little things" the real hobby enthusiats might need. They mostly cater to to the young crowd that buys tape recorders and other noisy stuff. I wanted to obtain a digital voltmeter only I had once seen in the U.S. -ala your tach you posted about some three weeks ago- to install in my car -it was a 2"by1.5"- besides the old ammeter system but they've never seen it. Went to the JY and snatched one out of a minivan and put it in.
Now I have both ampers and volts indication on my dash.

From your last post, I think I will leave the original cap as is and see what happens.

Will be in touch.

_________________
Rafa

Hecho en México

Ok! built two solid state 7005 regulators as per instructions in articles on other board -Moparts Tech Archives- with IC's from Steren P/N MC7805CT Positive volt reg, three prong, 5 volts, 1 amp. Did not install the new 10uF capacitor called for in the instructions but kept the original .47uF in the PCB.
Output, however is not 5V but 7.8V on both units I built. Did I do anything wrong or is this slightly higher voltage Ok?
Installed the regulators in the instrument panel and IC output voltage at the gauge terminals, both fuel and temp, is the car's battery voltage. 12V with engine off and goes up to 14V as the engine is revved up.
The needle or pointer for the fuel shows the same position as with the old worn out voltage limiter.
Now What?...
Shall I go out and buy a new analog IVR? ha ha
Thanks for your input.

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Rafa

Hecho en México

Whoa 7.8 is waaaaaaaaay off. Max out of those things should be like 5.05! You should be able to put 12v on the input, ground the tab or middle pin and the 3rd should output ~5v +/- 0.1 at the absolute max without any caps at all.

Don't hook anything up to your gauges again untill you get it sorted out. You risk blowing your gauges. 7.8v is over 150% of the original voltage.

Take a picture or draw me a schematic of exactly how you did things. Maybe you got the input and output pins mixed up? With the tab pointing up, the legs down, and the writing towards you, the leftmost is input, middle ground, right is output.

That's exactly how they are done...

Right like this photo.
Leftmost leg wired/soldered to the imput leg or "Ign" prong on center of the bakelite insulator, center leg soldered directly to the case and right leg wired/soldered to the output leg or "control" prong of the bakelite insulator.
I'm sorry I can't take/post a picture; somebody took my digital camera from my car never to see it again and have not had a chance (translate that $) to get another one.

On another note, this evening I removed the fuel gauge from the panel, applied 5VDC (4 NiCd batteries connected in series) directly to its terminals and the needle did not go beyond 7/8 of the scale. Maybe this is the problem and not the IVR.
With a good sending unit, 69.3 ohms "empty" and 12.7 ohms "full", (actuated by hand) I recalibrated the gauge to read just below the empty mark and just above the full mark and when power is removed the needle goes before the "E". I went shopping for an Echlin IVR but did not have time to install tonight. Will do tomorrow, fill the tank and see if that was it.
See you then.

_________________
Rafa

Hecho en México

P/N MC7805CT (Linear Integrated Circuit)
Regulador de voltaje positivo, 3 terminales, de 5 Volts, 1 Amper y encapsulado T-221A

This is the IC by Steren that puts out 7.8V from a 12V input.

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Rafa

Hecho en México

Seis I agree your gauge might be messed up but you have to take care of it one problem at a time. Its likely that a bad regulator caused the gauge to go bust. Assuming the regulator is good there is no way it should be putting out that much. I suggest you hook it up directly to the car battery and measure the output to eliminate the regulator itself.

FYI putting batteries directly to meter is a good test but do not do that for too long because the coil inside will melt. Leave at least 10-12 ohms (the lowest the sending unit will go) resistance in series with the meter so the gauge wont burn up.

EDIT:
Just thought of this, look on the device itself and make sure it says 7805 not a 7808. If they aren't labeld you probably got the wrong part. Also, these style regulators need at least 2 or 3 v more then their output voltage on the input for them to function, so do not hook up your 4 batteries to the regulator and expect it to work, you'd need 6 or 7 in series.

If you can't get the right reg., perhaps I can send you one.

First of all, a high output on the regulator would make the gauges read high, not low. By all means, fix the regulator, but that is not the only problem. Sounds like the gauges are bad.

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Chuck Rivers, Webmaster

My goof!
IC's 7805 were Ok; I was taking voltage readings at the wrong prongs
Sorry for the long delay in letting you know the outcome but two weekends of rain and other chores prevented me from "working" on the cars, but everything is ok now.
Solid state IVR's output is a solid 4.93 VDC -digital multimeter- without any changes or deviations as engine is revved and battery voltage increases or a load is applied. That's very good.
Gauges are all ok too and they have been adjusted to read right on the F\ mark with a full tank and right on the E/ mark when the float hits the bottom of the tank, this way I know I only have about 5/8 of an inch fuel level in the tank. Time for refilling before the pump beggins to suck air.
The problem actually was in the analog voltage limiters on-off-on-off function; One was on-off for about 160 times per minute with longer off times. Two others were on-off 80-85 times per minute with longer off than on times and were sometimes erratic, staying on-off even longer. One more was on-off only about 45 times per minute also with longer off than on times. These four have been converted to solid state.
Still have two more analog voltage limiters that are on-off from 60 to 65 times per minute with relatively equal on-off times and behave as they should.
Thank you Pierre for your input. Was very helpfull.
Thank you Chuck for your kind offer to send me an IC if needed.
Cheers!

¡Salud!

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Rafa

Hecho en México

Good going on the fix. Those old regulators can vary a lot, as you found out.

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Chuck Rivers, Webmaster