If you are going to use a VR like the 7805 or 7806 then it does not mater if the resistance wire is in the circuit or not. The VR's just need to be supplied with a voltage that is 2V or so above the VR rating. For example the 7805 needs at least 7V and up to 30V or so. In fact having the resistance wire there is better as the lower input voltage will generate less heat in the device.

 

81 - We are very close in our understanding of the circuit, with but these differences:

I agree the resistance wires vary, but that is of no consequence. I picked 8.66 ohms because it made the math easier when the other resistor was 7.33 ohms - I can remember 16.000 ohms. But, the exact value of the resistance wire makes no difference in a voltage-regulated circuit.


I actually fully agree with what you said, but want to point out to the others that you said the voltage "averages" 5.5 volts. Not that it is regulated to 5.5 volts. But, at various points during that time the voltage will be 0.0 when the ICVR is open, and as high as 20 volts due to the EMP spike as shown on the scope earlier.

I disagree. If we assume that Ford was right and the voltage truly averages 5.5 volts, then the gauges will read exactly the same if they are fed a regulated 5.5 volts. That is because the gauges work off heat and actually integrate the area under the voltage curve. So, when the "curve" is flat they still integrate and get the same answer.

I, too, would like a plug & play solution, and if Kevin is right (see below) we can have that.

The problem is the voltage drop across the regulator and the in-line resistance. If we use your number of a 2 volt drop across the regulator and use 81's 5.5 volts out of the regulator we would need 7.5 volts into the regulator. But, assuming the in-line resistor is the 8.6 ohms I was using earlier, we will have 6.4 volts into the regulator with the engine off if the gauges are pulling .75 amp. (12.8 volts -(.75 x 8.6))

I calculated previously that the gauges would pull .9 amp with the ICVR's contacts closed, but that would obviously peg the gauges if fed that continuously. I don't think we know what the current will be with regulated voltage, but being able to use the in-line resistor will be close.

 

5 pages to go!

I can feel the micro-analyticism! Yes, I made that up.

Seriously, you guys talking about all these measurements and stuff make my head spin.

 

Do you read lips? But, I think that's a good word! I'll have to ask my wife if Words With Friends would accept it.

 

I was looking forward to a Micro-analysis joke, but I see somebody beat me to it.

That's what I get for staying off of the computer and actually working on my truck.

 

The 7.5V is a bit close. The 2940 series has much lower dropout voltage. ~0.5 volts.

http://www.ti.com/lit/ds/symlink/lm2940-n.pdf

Also my '86 shop manual says the IVR output is 5.0 V not 5.5V

 

It does with the factory ICVR because of the nature of the thing. The heating element. Possibly why it has an adjustment in the first place.

I agree with an electronic ICVR type, it wouldn't matter unless you overloaded it. "pifft" Why you could theoretically do away with the resistor wire altogether, but should work it into the design for simplicity of plug and play.

I understand what you are saying now. I agree with that.

I misread what you meant by fixed in the last post. If it was fixed it would be like adding a resistor instead of a regulator.

My ford manual states 5.5v. Uggh...

Stangrcr1, built a working model using 5.0 volts and the gauges read lower than they did originally. I'm thinking 5.5 would fix that lower reading.

I hate it when Ford does conflicting info like that though...

 

The ICVR is a PWM(pulse width modulated) voltage regulator. With out looking at the schematics I don't know if it is a current or voltage feedback. Going to check into that again...

Its been years since I last played with them. I do rember using aprox 7Vdc to the cluster gave me good results(this was 20 years ago so I don't rember what I used).

Rember these guages ARE NOT accurate! I have swapped clusters and seen the guages read higher or lower than the previous one using the same sending units.
Every truck or car I own I don't trust the fuel guage under 1/4 tank for those reasons.

Thats way I go with the ole mechanical oil and bulb temp guages.

 

Yes, that probably has something to do with swapping to a different ICVR when doing the cluster swap. The factory ones are adjustable and can be adjusted for small variances. That would explain why this happens.


For what these gauges are, they are meant to be accurate to a given set of voltage and resistance values. Oil and water in the normal range is fine. Anything out of that range is not good. The Fuel gauge should read empty before the tank is actually empty by design.

If they do not function this way, there are test proceedures and repair proceedures to fix them so that they will work that way.

They were never designed for exact readings, otherwise they would have oil pressure and water temp scales.


That is good advise at any rate. The gauge systems on our trucks have outlived their designed lifespan. 5-10 years.

And as you say, they are not very comprehensive or accurate like a proper scaled gauge.

The purpose of the discussion is to create a electronic ICVR that will alow the gauges to be as acurate as the originals to their original set values.

We are not looking for perfection, because these gauges by design, cannot deliver that.

 

Yeah, I have two documents, one saying 5.0 and one saying 5.5. Of course, they didn't bother to say how to measure that.

Yes, Stangcr1 does have that 5.0 unit in service and it has fixed the wandering readings, they are just all low. He, like me, has the parts to make a variable unit, but just hasn't taken the time. I sure understand that.

I don't know if I would call it voltage or current feedback. Instead I would call it crude. The regulation comes via the in-line resistor and the ICVR combined. The gauge/sender combo's pull the input voltage down to the ICVR by their current draw across that resistor. The lower the voltage into the ICVR the longer the points stay closed since the heater pulls less current.

I agree the factory gauges are not accurate, but I think they could be more accurate given stable voltage. Having said that, I just installed a mechanical temp gauge on Dad's truck since the factory gauge has been showing it running too warm. It isn't running as warm as the factory gauge indicates, but I've watched the factory gauge move while the mechanical gauge has been steady. At least I have something I can rely upon. In fact, if I had a fuel gauge that matches the temp, pressure, and volt meter I have I'd install them in the factory cluster.

 

Yes and no.

I did build the 7805 ICVR and it holds a steady 4.96v in the truck. All my gauges read approx 1/8th lower than with the stock ICVR. It has been in there since I started that thread months ago. Gages are rock steady with it.

I also did build an adjustable ICVR with an LM338 chip. I have it bench set for 5.3v. Just never got around to putting it in the truck. The problem with the LM338 is finding a resistor/potentiometer set that will keep the range within a couple volts. Tiny adjustments of this potentiometer swing the voltage a lot. I suppose I could have put a resistor inline before the pot to trim it, but never got to it. I probably have enough parts to make 10 ICVRs based on the LM338...

I have had so many other projects come up to even mess with this in my truck.

 

The voltage swings are why I think an adjustable regulator should use precision resistors to set the voltage. We just need to figure out what that voltage should be and then nail it so it cannot change.

 

Here is an awesome site with the resistance values already figured.

Once the voltage required is figured out, plugin the resistors and done.

 

Cool! Thanks. By the way, the ICVR on these gauges is having problems, so making the regulator is highly likely.

 

I had wanted to make an ICVR with the LM338 that would only adjust 5v - 6v. I got lazy and just threw together what I had and the wide range of the potentiometer I used makes it hard to get fine adjustment.

You are giving me the nudge to put it in and see what happens...

Maybe this weekend....