North American Turbocoupe Organization



Solid State IVR
Walsted Offline
Posting Freak
#1
I checked around on the web, and found a solid state IVR set-up here that is different from what is in our technical articles page. This article says to use tantalum-dipped capacitors from input to ground (1uF) and output to ground (10uF) on the 7805 and not use a resistor.

The head electronics repairman at work thinks that this would be the best way to get a constant five volts. Since I have read in a couple of posts that the gauges read low after using the method listed in the technical articles, I am most likely going to try the capacitor method with my spare IVR. Before I do, though, has anyone else already tried it?

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Mike Walsted - NATO member
1986 5-speed TurboCoupe .

[This message has been edited by Walsted (edited 02-23-2002).]
Mike Walsted - Sold my 1986 5-speed TurboCoupe
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N8 Offline
Member
#2
OK, Here a few things to consider. You don't want the gauges to get a constant 5 VDC, here's why. As described in the TA, the inst. cluster was built to run on "pulsed 12 VDC." This is currently provided by the stock IVR, which is nothing more than a current controlled thermocouple relay, with an adjustment screw that controls the on/off cycle of the thermocouple mechanism. When using the SSIVR in the TA, the gauges will read lower than normal. This is due to the fact that even though the 5 VDC is more accurate and stable, it's still only 5 VDC, not the 12 VDC that the gauges need. Regardless of what type of voltage adapter you install, you're not going to change the "load" (resistance) of the instrument cluster. So, the load being the same, changing the voltage must change the current, (which is the only other variable in a DC circuit.) 12 volts will always pull more current than 5 volts, less voltage = less current, less current = less power, which causes "degraded" operational capability, (low readings!) Now, a constant 12 VDC will burn up the gauges. The correct approach would be to obtain the stock IVR from a properly functioning inst. cluster. Use an O-scope to find the frequency it operates at, and the approximate wave form it produces.
From this info, you can build a regulator/pulse 12 VDC circuit with Radio Shack components. It might even fit in the oringinal IVR "can."

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N8, FLY FORD!

[This message has been edited by N8 (edited 02-23-2002).]
N8, FLY FORD!
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tylerport Offline
Senior Member
#3
Now if we could find someone to understand what N8 just said, we'd be in business! Just kidding N8! Any one have an oscilloscope handy?

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Jim Portteus
NATO Member
86 Turbo Coupe, 131K Miles, 140MPH Speedo, Gillis Valve, 2 1/2" Downpipe to 2" Duals w/ 18" Glasspacks, 245/50R16's and new paint.
Jim Portteus
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Walsted Offline
Posting Freak
#4
Quote:Originally posted by tylerport:
...Any one have an oscilloscope handy?
Well, I gave away my O-scope after when I realized that I couldn't fix the bad CRT, but not before I found out why you shouldn't touch the big blue capacitor inside immediately after unplugging the O-scope. Helluva way to learn about capacitors.

I'll try to get one of the electronics guys at my office to figure out the output one day when they are bored. I might try the dual capacitor method, anyway. From what I understand (but I forget from where), the gauges are 250mA. If this is correct, wouldn't the 1 amp voltage regulator supply sufficient current/amperage if the gauges are really 5V 250mA?

N8: What burns up gauges - amps, volts or watts? Higher and lower amperage voltage regulators are available, as well as with different voltages. My goal is to get a cheap, dependable constant voltage without the pulsing. Any suggestions?

Thanks
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Mike Walsted - NATO member
1986 5-speed TurboCoupe .

[This message has been edited by Walsted (edited 02-23-2002).]
Mike Walsted - Sold my 1986 5-speed TurboCoupe
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segfaultxr7 Offline
Posting Freak
#5
Quote:Originally posted by Walsted:
N8: What burns up gauges - amps, volts or watts? Higher and lower amperage voltage regulators are available, as well as with different voltages. My goal is to get a cheap, dependable constant voltage [b]without the pulsing. Any suggestions?
[/B]

When you see a current (amp) or wattage rating on a voltage regulator or something, that is an indication of how much power it is capable of providing. OTOH, something that uses power has an amp or watt rating indicating how much power it does draw. For example a table lamp might have a 100 watt ratting; that indicates the power it CAN safely provide, although you can use a bulb that draws only 15 watts if you desire. So, as long as you have a voltage regulator that has a rating equal to or higher than the gauge cluster's requirements, you're fine.

Also, if the 5 volt regulator makes the gauges too low, I don't see anything at all wrong with setting them up to run at 5.5 or 6 volts.

What do the capacitors do, anyway? Do they let you fine-tune the voltage output?
88 TC 5-speed
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Walsted Offline
Posting Freak
#6
Quote:Originally posted by segfaultxr7:
When you see a current (amp) or wattage rating on a voltage regulator or something, that is an indication of how much power it is capable of providing. OTOH, something that uses power has an amp or watt rating indicating how much power it does draw.
So, since I hear that the gauges draw 250mA each at full deflection, and the voltage regulator supplies 1 amp, and 3x250mA is less than 1 amp, I should be okay?

Quote:What do the capacitors do, anyway? Do they let you fine-tune the voltage output?
From what I can gather, they absorb voltage spikes. I asked around, and did a lot of google.com searches, and from what I can tell, they need to be the tantalum dipped capacitors to be worthwhile. On the other hand, I couldn't find any justification for the 10uF on the 5V side, but the link referenced above has it, and since he says it works for him, that will be how I try it first.


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Mike Walsted - NATO member
1986 5-speed TurboCoupe .
Mike Walsted - Sold my 1986 5-speed TurboCoupe
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segfaultxr7 Offline
Posting Freak
#7
Quote:Originally posted by Walsted:
So, since I hear that the gauges draw 250mA each at full deflection, and the voltage regulator supplies 1 amp, and 3x250mA is less than 1 amp, I should be okay?

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From what I can gather, they absorb voltage spikes. I asked around, and did a lot of google.com searches, and from what I can tell, they need to be the tantalum dipped capacitors to be worthwhile. On the other hand, I couldn't find any justification for the 10uF on the 5V side, but the link referenced above has it, and since he says it works for him, that will be how I try it first.



Yes, assuming those gauge current figures are accurate, you will be fine. As long as the current rating is for more than what the gauges draw, it'll be perfect.

The capacitors absorbing voltage spikes makes sense. I was thinking about something different. As long as there is enough capacitance to filter out the transients, you're fine. 10uf should be sufficient as the regulator output is pretty steady--that's the point of using it in the first place. [Image: smile.gif]
88 TC 5-speed
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N8 Offline
Member
#8
OK, I see a little training is in order. Imagine a 100 gallon water tank with, oh say, a 1 foot diameter pipeline connected at the base of the tank. And for demonstration purposes, volts = pounds per sqaure inch, (psi,) and amps = cubic feet per minute, (cfm.) Now, we'll say that this 100 gallons of water exerts a force of 90 psi at the bottom area of the tank. Therefore, at the opening of our pipeline (circuit) we have a force of 90 psi (volts.) OK, so 90 psi on a 1 foot diameter (wire gauge,) pipeline (circuit,) causes the water in the pipe to flow at 75 cfm (amps.) The only real difference between this example and an eletrical circuit, is that water will flow anywhere you let it. Electrons flow only in a loop, (i.e. negative to positive.) The only exception being static electricity.
Now, if your 1 ft. dia. pipe flowed through a reducer into a 6 inch dia. pipe, the 90 psi will still force the water to flow at 75 cfm, but, since the pipe is now half the volume (wire gauge,) the water has to flow twice as fast. This is all fine and dandy with water because water absorbs heat. Electrons however, do not, but instead the motion (flow) of electrons produces heat. That is why you must have a large enough wire to handle the amount of electrons you need it to carry, while at the same time having a large enough surface area to radiate away the heat. This might also help. Let's discuss a coulomb. This is a specific number (amount) of electrons. It's something like 6.18 to the 10th power (61,800,000,000) electrons. When 1 coulomb of electrons passes any one given point in a circuit in a time of 1 second, that is 1 "ampere" or amp. And if I remember correctly, a "volt" is defined as: the force required to cause a 1 amp flow of electrons in a circuit having a resistance of 1 ohm, this equals 1 volt.
About the little incident with the O-scope capacitor. Capacitors are little "electron banks", kind of like a "one shot" battery. And yes, they can kill you. It only takes 500 milliamps (1/2 amp) to kill you, provided that 1/2 amp goes accross you heart, (like in one hand and out the other.) It causes irregular heartbeat and eventually (usually with-in 2-4 days,) heart defibrulation and DEATH! So if you get zapped in this manner, I highly recommend going to the hospital for an EKG. And especially if it was A/C electricity, an EKG is a must!
MW, there are about 5 different types of capictors. They all do the same thing but posses different properties, kind of like the different types of 18 wheelers, (tankers, flatbeds, box trailers, hoppers and cryo-huaulers.) They all carry loads, but in different ways, each having it's own special use.
On the SSIVR, I really can't come up with any easy/cheap way to get away from having to pulse the 12 vdc to the IC. But, a compact and reliable pulsing CKT wouldn't be that hard to put together.
Sorry that this is so long. But unless you're actually interested, you probably didn't get this far.
N8.


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N8, FLY FORD!

[This message has been edited by N8 (edited 02-24-2002).]
N8, FLY FORD!
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BJL Offline
Moderator
#9
whoaaaaaaaa.
that Applied Physics class i took last year actually made me understand that!
N8, are you a teacher? Just wondering


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Brian J Larkin
1988 Turbo Coupe 5spd, dark blue and shining like a peice of polished glass.
http://crazydriver358.5u.com
Brian Larkin
88TC 330,000 miles
Slightly Modified
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N8 Offline
Member
#10
AIRCRAFT ELECTRONICS TECHNICIAN


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N8, FLY FORD!
N8, FLY FORD!
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