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Discussion Starter #1
Hello,

I'm trying to troubleshoot the cause of a low reading on the temperature gauge. The voltage reading I get at the sending unit wire pulses from 0 to 2-1/2 to 3 volts. Reading on-line, I see where people are saying it should be 5 volts, so I ordered a new IVR from Mustangs Unlimited. The on line catalog said it was a constant voltage type, but what I received says it is the bimetallic type and will pulse to 2-1/2 to 3 volts. Well, heck, I got that already. So what's the voltage really supposed to be? Is it 5v or 2-1/2 to 3?

The oil pressure gauge seems to be OK. The fuel gauge is irratic. Sometimes it works. Sometimes it don't. When it does work it reads somewhat low. The temperature gauge reads low all the time. Even when the car is trying to overheat (Another issue), the gauge barely climbs inside the normal range. Sending unit looks fairly new. Gauge will go full scale when wire is grounded. Problem may be the sending unit, but I'm concerned about my voltage.

Any help would be appreciated.

Thanks,

Hal Davis
 

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It is actually 12 volts that pulsates and gives an "average" of 5 volts to the slow reacting instrument gauges.

I made a solid state one for less than 5 dollars. Here is a write up and pictures:
IVR

There is a forum member that sells premade adjustable SOLID STATE regulators on ebay for $25 and many people are happy with them.
http://cgi.ebay.com/ebaymotors/Ford...ptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories

Good Luck and BE Safe
Ron
 

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Ron,

Glad you replied on this one. As you know, I have used your plans for the IVR you designed in the past, with the adjustable voltage, to great success, still using that one in the 66 coupe.

I went the lazy route for the 66 convertible, and bought from the fellow on Ebay. Let me tell you, a total quality product, top notch product! Adjustable too.

The fellow that makes them, or sells them, he is a really good guy, I have dealt with him on this and other items- you cannot go wrong buying from him.

If you choose to build one from Ron's plans, the cost is probably slightly less, but you have to hunt the parts down, a small consideration.
 

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Hello,

I'm trying to troubleshoot the cause of a low reading on the temperature gauge. The voltage reading I get at the sending unit wire pulses from 0 to 2-1/2 to 3 volts. Reading on-line, I see where people are saying it should be 5 volts, so I ordered a new IVR from Mustangs Unlimited. The on line catalog said it was a constant voltage type, but what I received says it is the bimetallic type and will pulse to 2-1/2 to 3 volts. Well, heck, I got that already. So what's the voltage really supposed to be? Is it 5v or 2-1/2 to 3?

The oil pressure gauge seems to be OK. The fuel gauge is irratic. Sometimes it works. Sometimes it don't. When it does work it reads somewhat low. The temperature gauge reads low all the time. Even when the car is trying to overheat (Another issue), the gauge barely climbs inside the normal range. Sending unit looks fairly new. Gauge will go full scale when wire is grounded. Problem may be the sending unit, but I'm concerned about my voltage.

Any help would be appreciated.

Thanks,

Hal Davis
Hal
Like mentioned before 5v is the avg. Those readings are ok. The problem is the meter takes a picture about 4 or 5 times a second. Whatever it captures in that picture it avg it out and displays it on the screen. The refresh rate is about 4 times a sec. The ivr flashes to a different tune. So the meter cant really judge whats going on because its not synchronized to the ivr. I have an avg meter, and it even has a hard time trying to capture the 5v avg. The only way I have done it with is a scopemeter. I can change the timebase to reflect whats going on with the IVR. Hope that helps...


Ivan

YouTube - ‪VIDEO0009‬‏
 

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Discussion Starter #5
Thanks for the response guys. Maybe it doesn't matter, but I was using an analog voltmeter when I took the readings, as my digital indeed was giving reading all over the board. The needle on the analog voltmeter bounces from 0 to to 2-1/2 and sometimes up to 3, but wouldn't that be an average of something like 1-1/2 volts? Maybe I'm thinking about it wrong?

Thanks again,

Hal
 

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One thing that can effect your readings is the quality of ground for the IVR and the same for your meter lead. ic237 explained the rest very well.
 

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Thanks for the response guys. Maybe it doesn't matter, but I was using an analog voltmeter when I took the readings, as my digital indeed was giving reading all over the board. The needle on the analog voltmeter bounces from 0 to to 2-1/2 and sometimes up to 3, but wouldn't that be an average of something like 1-1/2 volts? Maybe I'm thinking about it wrong?

Thanks again,

Hal
Hal
Take your meter off of autorange and the digital meter will show you the 12ish and zeroish readings (on-off-off). The avg meter is slow reacting and the deflection of the needle's weight is causing you grief.
 

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There is average and then there is 'average'. What you want is called RMS voltage, root mean squared. (The square ROOT of the MEAN [average] voltage SQUARED.) These gauges are reacting to heat generated from applied voltage. Heat is an indication of power and the power generated by a voltage is proportional to the SQUARE of the voltage, not the voltage itself. (Power = Voltage * Voltage / Resistance) I'll explain using Ivan's o-scope trace shown above as best I can read the scales from 2000 miles away. :)

That shows a 13.1V pulse lasting for about 0.14 seconds that is repeated every 0.86 seconds (1.16 times per second). The pulse width and rate may well vary with each and every CVR; its only the 'average' value that counts. You square the voltage, multiply it by the ratio of on time to cycle time and take the square root.

13.1 * 13.1 * .14 / .86 = 27.94
Square root (27.94) = 5.29 V

The average heating value of that output is 5.29 V. If you take only the average voltage its:

13.1 * .14 / .86 = 2.13 V

So what you read with a meter depends greatly upon what meter you are using and how that meter works. You can't really measure it and have it mean anything without an oscilloscope or a true RMS meter which you are not likely to find. (To be accurate, a typical RMS meter has to have sine wave input voltages since that is how it was calibrated. A CVR output is a far cry from being a sine wave voltage so having an 'RMS meter' wouldn't work either.)

The DC voltage you would use to make the gauges work like they did using a CVR is somewhere between 5 and 6 V. The 5.29V above may not be accurate for a variety of reasons and that is why the variable voltage, solid state units are preferred to a fixed voltage one. You can adjust their output voltage to make the gauges read correctly. Changing the voltage from 5V to 6V causes the gauge reading to increase by 44% so its a fairly finicky adjustment.
 

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Discussion Starter #9
Thanks for the explanation! Sounds like my IVR is OK.

Today, I installed a new temperature sending unit but it still behaves the same. Pretty much shows no reading on the gauge unless I get on the interstate and do 70 on a 95 degree day. Then it will climb just a hair and maybe reach the line on the left side of the normal zone, but that's it. Shut if off and start it back up in a few minutes and it will go about half scale from sitting with a hot engine, but immediately goes back to cold when water starts circulating. If you ground the sending unit wire, the gauge will go full scale. Oil pressure gauge reads just fine. Any suggestions?

Thanks,

Hal
 

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Here is another video of how much it changes

I typically Average out the True RMS values over time.
It generally around 5


The top left corner readings is:
AC+DC (True RMS)

Top right: VPWM
readings show the effective voltage based
on the average value of samples over a
whole number of periods of the fundamental

frequency

Bottom Left: HZ

Bottom Right: On time

YouTube - ‪SANY0015.MP4‬‏
 

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Interesting. Cycle rate varies more than I would have thought. Is that an original CVR or one of the repros? Also, is that in a running car or with a power supply on the bench?

The upper left voltage number varies all over from 5.0 to 6.5 V. My eye sees the average as maybe 5.8V. Its rarely below 5.5 and rarely over 6.0. Since the gauge response time is seconds those variations never show up in the needle movements.
 

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Interesting. Cycle rate varies more than I would have thought. Is that an original CVR or one of the repros? Also, is that in a running car or with a power supply on the bench?

The upper left voltage number varies all over from 5.0 to 6.5 V. My eye sees the average as maybe 5.8V. Its rarely below 5.5 and rarely over 6.0. Since the gauge response time is seconds those variations never show up in the needle movements.
Its an oldie. That swing is based on one pulse. If I zoom out and have 3 or more pulses the number are a bit more stable. The regulator is stable only when its flat and still on my desk. Any slight shaking and it looks like a frequency drive.
 
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