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  #11  
Old 05-19-2012, 07:30 AM
kevin_tbird kevin_tbird is offline
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Before I go to the IVR3 I'd like to get the stock style working. This car has everything stock, right down to the correct style screws that you cannot see.

Simply connected: I'm not trying to bypass the problem I'm trying to diagnose it. Working with the electrical guy from the Birds Nest seemed to be the best way. I'm glad for your help.

The duty cycle we are talking is adjustable on the stock style CVRs. The average voltage was below 5v on two differ CVRs when bench tested (using a 12v bulb as a load and analog gauge. Increasing the duty cycle got us to about 5.5v average. The other way tjo check was that the test light would come on only about 30% of the time, not 50%. Of the two CVRs one was in the vehicle for at least the last 40 years and one was brand new.

I've checked resistance on each sensor feed wire. Great continuity and no resistance for both of them. Neither was shorted to ground.

The gauges both work on the bench using the gauge itself as the load and tapping a 12v source on and off with the sensor wires connected to ground.

With the CVR in the vehicle ( frame not grounded ) the gauges work fine - registering correct values. When I grounded the CVR body with a jumper wire the fuel gauge slowly dropped to near zero and the temp gauge went their immediately ( yes I was running the car at the time to check the accuracy of the temp gauge.

So instead of throwing parts at the problem (it may come to that) lets try and figure out why a ground at the CVR frame is necessary and why it would make a difference to the gauge output. I'm glad to build a bench setup if we can come up with a good idea on how to test.

Thanks
Kevin
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  #12  
Old 05-19-2012, 12:35 PM
Joe Johnston Joe Johnston is online now
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I'm gettin' more confuseder than ever since reading these posts along with my +6V ground vrs 12- ground post and the links mentioned therein.

1) I understand the importance of good grounds but fail to see how they are any more important than good corrosion free hot wire connections. As I see it the only difference is the ground is in our old non plastic component cars is part of the structrue of the component. Would a component work better with 3 power leads to it, and if so how reduntant can we become in establishing grounds? Does each component need a separate ground wire like new vehicles with all the plastic components? If multiple grounds are so essential, lets make the cars from copper like the wiring, wouldn't that be better? (understand I mean in theory not economically).

2) I see frequent mention of the CVR being 6V and 5V here and other places. My old Little T-Birds nedded no CVR and I know they were 6V or 12V guages depending on the year of the vehicle and the incompatability of mixing 55 & 56 components in the dash.

3) I see mentioned some CVR's not working with "our cars". Is that because they put out an average of 6V instead of 5V? If so, that means Ford changed from their original 6V guages, then to 12V guages and then to 5V guages while having 5V guages in Thunderbirds and 6V guages in their other cars and trucks at the same time. Econoomics doesn't support that, or does it and I don't comprehend.

4) Mentioned in the other post was the fact that economics came into play as well as standardization to make the decision to have a - ground system. Having a 5V in a Thunderbird and 6V guages in cars and trucks at the same time for nearly identical parts certainly doesn't seem to be economical.

At the beginning of one of the links posted the phrase "Opening a can of worms" was stated. Someone straighten me out because I see a lot of contridiction in the info and am confused over something that should be rather cut and dried.
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  #13  
Old 05-19-2012, 01:46 PM
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Default Constant Voltage Regulator

Sorry for any confusion I might have caused regarding 5v-6v CVR's. The gauges in our Squarebirds (and other Tbird models after that, I think) were 6v gauges. That required the use of the Constant Voltage Regulator to drop the 12v in these cars to something between 5v-6v. I often used 6v as the figure, but the articles written about the CVR use 5v. It is my understanding the the CVR internal system drops that 12v to something that the 6v gauges can handle, averaging 5-6v using a 50% duty cycle if I have this right. As Dave said, new solid state CVR devices, give you a steady 6v output. I don't know if this is gonna clear things up or not. Maybe Dave can, if I didn't.
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  #14  
Old 05-19-2012, 02:40 PM
Jimz Bird Jimz Bird is offline
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Well, let's see if I can confuse it more.

This is just Baby Bird stuff but I "think" it will apply from the 57 up which has the CVR.

55 is of course 6V and no CVR needed. You can use a 6V "Lantern" battery to check the gauge and it should go to full. If you measure the resistance across the terminals it will measure 11-12 ohms.

56 is a 12V gauge and while it looks the same as a 55, it isn't and won't work in a 55. It is a 12 volt gauge but the resistance across the terminals is 38-40 ohms so it is "internally" voltage reduced to function like a 6V gauge. This was the only year the Tbird has a 12V gauge. Again, no CVR needed.

The 56 passenger car gauge is also 12V and is similar to the 57 style Tbird but won't work in the 57 because - here we go - 57 started using the CVR and the gauge in the 57 is a 6V with a resistance reading of 13-14 ohms. The 57 CVR reduces the 12V to 6V.

The CVR is at times referred to as an "Instrument Voltage Drop Regulator" or a "pulsating voltage drop bi-metallic power regulator".

A caution from the 55-57 Restoration Manual when checking the CVR:
"The "pulsating voltage drop bi-metallic power regulator" provides reduced voltage (max 9V) to the fuel and temperature gauges. CAUTION, this unit must be installed and grounded with mount screws prior to operation check or applying voltage. If power is applied without a ground the unit sends 12V to the fuel and temperature gauges causing both gauges to fail."

Now we have from 5-9V. Probably the resistance in the sending units ties in to this somehow.

Once again @Dave D et al. for clarification.

There ya go Joe, clear as mud?
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  #15  
Old 05-19-2012, 05:04 PM
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You're on the money as usual, Jim. 1956 (Ford, Lincoln, Mercury, & Trucks) is the ONLY year for 12-V gauges. (I didn't believe this at first, until the Master Parts Cat's proved it.)

It's all about 'duty cycle' (the 'on' time vs the 'off' time). Battery wires and starter motors are grossly undersized but they are only on for seconds, then off for many minuites.

Back then, Ford could not use a simple current dropping resistor because the currents change from "F" to "E" and from "C" to "H". Both gauges are in parallel, so 'constant voltage' was easier to achieve by using slow gauge movements and an average voltage.

Ford also used a bi-metal strip with a contact in your gas tank sending unit. So, a cycling voltage source was connected in series with a gauge and a gas tank unit that used current to cycle, causing your gauge reading. Cold days would initially show less gas than hot days.

So, CVR cycles need to be very regular. That's why it needs a solid ground. Full 12-Volts is applied to the gauges, but only for half the time. The 1955 T-bird system is 100% duty cycle at six volts, which is exactly the same power without a CVR. - Dave
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  #16  
Old 05-19-2012, 05:50 PM
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Back to my vehicle. After adjusting the CVR it is running at about 50% duty cycle and cycling between 0v and 12v. The question is why the GAUGE performs differently when the CVR is grounded.

I'm wondering if I could have a short to ground inside the gauge, but am not sure how to tell. I cannot find any specs for internal resistance in the gauge.

To be clear 12v is supplied to the CVR 100% of the time and 12v is supplied to the gauge about 50% of the time.

Kevin

Last edited by kevin_tbird : 05-20-2012 at 09:34 AM.
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  #17  
Old 05-19-2012, 08:05 PM
Jimz Bird Jimz Bird is offline
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Keven,

Sorry about rambling on

Have you tried the 6V Lantern battery to see if that cause the gauge to sweep? Actually 3V should give you about a quarter of the way up the scale and 4V about 3/4 of the way. The lantern batter is just a bit easier to use due to the spacing of the terminals.

What is the resistance between the terminals of the gauge.

It should be in the range of those listed.

"CAUTION, this unit must be installed and grounded with mount screws prior to operation check or applying voltage. If power is applied without a ground the unit sends 12V to the fuel and temperature gauges causing both gauges to fail."
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  #18  
Old 05-19-2012, 09:53 PM
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Quote:
Originally Posted by kevin_tbird View Post
...The duty cycle we are talking is adjustable on the stock style CVRs. The average voltage was below 5v on two differ CVRs when bench tested (using a 12v bulb as a load and analog gauge.
My understanding is, the factory CVR's are sealed and not adjustable. Here is one sold by rockauto.com:

I could be wrong buy why produce a CVR that outputs anything but 6-volts?

Quote:
Originally Posted by kevin_tbird View Post
...The gauges both work on the bench using the gauge itself as the load and tapping a 12v source on and off with the sensor wires connected to ground.
Kev, that's not how it works in your car. The gauge is simply another resistance in series with your fuel tank sensor. The tank sensor is like a turn signal flasher unit, with a bi-metal strip that opens and closes.

Quote:
Originally Posted by kevin_tbird View Post
...So instead of throwing parts at the problem (it may come to that) lets try and figure out why a ground at the CVR frame is necessary and why it would make a difference to the gauge output...
I totally agree. Inside your CVR is a bi-metal strip (a heater that flexes at regular intervals, like a turn signal flasher). It needs a feed and a ground to complete the 'flasher' path. Also on the bi-metal strip is your output wire. When the power is on, the strip makes and breaks a set of grounded contacts based on current flow. When the contacts open, your gauges see 12-volts. So let's check out the current to ground on your CVR.

Quote:
Originally Posted by kevin_tbird View Post
Back to my vehicle. After adjusting the CVR it is running at about 50% duty cycle and cycling between 0v and 12v. The question is why the GAUGE performs differently when the CVR is grounded.

I'm wondering if I could have a short to ground inside the gauge, but am not sure how to tell. I cannot find any specs for internal resistance in the gauge.
I think Jim gave you resistance values. BTW, your gauges are totally isolated from ground, so do a resistance check from the gauge post to ground.

You used a light bulb for a load? What kind of bulb? How many amps were going through it?
Use your meter to; check current coming into the CVR, current flowing through ground, and output current. Do these tests with the CVR connected to the proper sending units. An empty tank will have the highest resistance, but a full tank should have nearly zero resistance.

To verify proper currents, use 4 'D'-cells in series or a lantern battery to power your gauges with the ammeter connected in series.

Quote:
Originally Posted by kevin_tbird View Post
...To be clear 12v is supplied to the gauge 100% of the time and 12v is supplied to the gauge about 50% of the time...
Huh? Is this a possibility?
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  #19  
Old 05-20-2012, 10:36 AM
kevin_tbird kevin_tbird is offline
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Resistance readings at 72 degrees ambient. CVR and Gauge disconnected from vehicle.

CVR
IGN terminal to case 60.5 ohm
output terminal to case 60.5 ohm
IGN terminal to output terminal 0 ohm

Fuel gauge
post to post 12.6 ohms
no continuity to ground from either post

Temp gauge
post to post 12.5 ohm
no continuity to ground from either post

Next tests were performed using a Lantern battery outputting 6.16v.
Fuel gauge moves to just past 3/4 full
Temp Gauge moves to max.

Using two batteries to obtain an output voltage of 11.87v. Wiring the CVR in series with the gauge and grounding the CVR case to the battery the CVR produces 7v.

I.m now looking for some resisters to continue testing.
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  #20  
Old 05-20-2012, 12:56 PM
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It may be impossible to create modern solid state accuracy while using 50+ years old production mechanics. I've been following this thread with interest. My take is that the fuel gauge is at best, simply an indicator of the tank's remaining contents. My practical experience with most vintage auto instruments does not allow me to trust running things on empty.
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