Floating gages
Senior User
Joined: Feb 2012
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From: Grants Pass, OR
Just checked the gauges laying on the bench. All three show 12.5 ohms across the guage, and it doesn't change with reversed polarity, so I don't think the rest of the instrument panel nor the IVR is impacting those readings. Given that, any resistance of the sending unit, such as the 10 ohms full scale on the gas, would be added to the 12.5. IOW, we are looking at a minimum resistance of 22.5 ohms @ 5 volts = .22 amp.
I think I'll see if I can find the values of the other sending units.
I think I'll see if I can find the values of the other sending units.
FTE Legend
Joined: Jul 2010
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From: Northeast, OK
That's what I've done in the spreadsheet on a per gauge/sender basis. Picking the max current value for each pair gives a total of roughly 1/2 amp.
Post Fiend
Joined: Jul 2004
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From: Northern California
I guess while it is sometimes nice to know how the old system worked, I'm with Don - the IVR is old news. The real question is how does 4.95 volts run the gauges, meaning is it high enough to give accurate readings, and will the 7805 provide adequate current w/o overheating.
But, speaking of Don, did he get lost between his house and his truck? He said he was going out to try it about 6 hours ago.
But, speaking of Don, did he get lost between his house and his truck? He said he was going out to try it about 6 hours ago.
I'm skeptical that it's going to work satisfactory without some sort of potentiometer installed for adjustment of the output flow.
Without it for tweak adjustments, I foresee too low or too high of readings depending on vehicle.
Post Fiend
Joined: Jul 2004
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From: Northern California
It has been a while since I played with series and parallel circuits, but I'm pretty sure you can treat each gauge/sender pair as a separate circuit. In other words, we know the source voltage, the gauge resistance, and the sender's max resistance. E=IR so I=E/R. IOW, divide the combined resistance of the gauge and sender into 5 and you'll have the current of that pair.
That's what I've done in the spreadsheet on a per gauge/sender basis. Picking the max current value for each pair gives a total of roughly 1/2 amp.
That's what I've done in the spreadsheet on a per gauge/sender basis. Picking the max current value for each pair gives a total of roughly 1/2 amp.
Or you can treat them all as one circuit from the battery to the IVR to the gauges.
Just like one whole city block may be on one circuit from the power plant, there are many more circuits in your home on that block. Many circuits can branch off from one "main" circuit etc...
Ford treats them as one circuit from the IVR to the three gauges, and separate circuits from the gauges to the sending units.
FTE Legend
Joined: Jul 2010
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From: Northeast, OK
I'm pretty sure the readings won't be too high. Somewhere I've read that the IVR was supposed to give the equiv of 5.2 volts, so if that's true Don's 5.0 will give less current and slightly lower readings. But, I'm going from memory and that is dangerous. Anyway, I'm hoping his approach works well since it is a lot simpler than the adjustable one I planned to try - some day.
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Posting Guru
Joined: Jul 2010
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From: Marysville, WA
Bingo. While the EVTM may say 5v for the gages, I am thinking they need somewhere between 5v and 6v. Here is a pic of the gages with the truck warmed up.
All my gages are reading lower than before. The oil pressure and temp are both reading a full letter lower or more and the tank was just under full. I am wondering if the grounds are contributing to the low readings.
Sorry about the delay. Got sidetracked mowing the yard, taking the trash out, etc.
I also repainted all the needles with Safety Orange.
Going to look into an adjustable voltage regulator. My truck is the guinea pig for this experiment.
Anybody notice the Autometer Sport-Comp Voltmeter?
FTE Legend
Joined: Jul 2010
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From: Northeast, OK
So, Plan B? Adjustable regulator? I'm thinking we put a big capacitor on the output of the IVR to turn the square wave into pretty good DC. Should give the same current and therefore the same gauge readings as before, but we can read the voltage accurately with a DVM. Then we set the regulator for that.
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Posting Guru
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From: Marysville, WA
A big capacitor on the IVR would keep the gages on for a while after you shut off the truck.
Also, just how much current would it take to charge the cap and would that overload the IVR?
Also, just how much current would it take to charge the cap and would that overload the IVR?
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FTE Legend
Joined: Jul 2010
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From: Northeast, OK
I could try it with the instrument panel on the bench and put the scope on to see if we have DC. But, if you switch your DVM to AC and don't see anything then you have pretty decent DC.
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Posting Guru
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From: Marysville, WA
After installing a 1 farad cap in the son-in-laws car for his amp, yeah that is what I thought.
I am going to look into an adjustable power supply, unless I can find a 5.2v fixed...
I am going to look into an adjustable power supply, unless I can find a 5.2v fixed...
Posting Guru
Joined: Apr 2011
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From: Orlando area
Not to discourage you from your quest.
But Dennis Carpenter Restorations sells these Regulators for $15.
Dennis Carpenter Ford Car, F-100 Pickup Truck, 8N, 9N Tractor and Cushman Scooter Restoration Parts
But Dennis Carpenter Restorations sells these Regulators for $15.
Dennis Carpenter Ford Car, F-100 Pickup Truck, 8N, 9N Tractor and Cushman Scooter Restoration Parts
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Joined: Jan 2012
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From: Dallas, GA
I did notice the voltmeter...I like it!!! I left my Ammeter in place and installed a separate voltmeter...but I like the look you have better.
FTE Legend
Joined: Jul 2010
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From: Northeast, OK
Don - I'm not sure this will work, but I think you can raise the voltage .7 volts by placing a diode between the regulator and ground. Most diodes have a .7 volt forward voltage drop, so using a 1 amp unit would bias the regulator up that much.