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Mach1 Driver

Digital Voltage Regulator for gauges

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Has anyone tried one of these? On the pro side it gives you a rock solid 5v output, not the 12v pulsed output of the original, and that should be a good thing. On the negative side, I've heard of uncorroborated high failure rates. I could easily overcome that, but here is an unexpected consequence that gives me pause. It comes from a comment on another forum: 

66#3 said:

This (digital regulator) slowed the needle movement so that it took about 30 seconds to settle into its reading. For fuel, this is fine because consumption takes a long time. But for oil pressure, this is a deal breaker for me. I want to know to within 5 seconds of starting the engine if I have pressure so that, if not, I can shut it down.

Has anyone else experienced this additional 25 second delay of oil pressure? I can theorize why this delay occurs, but its all conjecture until I hang a voltmeter on the stock part.

 

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That delay is likely due to the resistor wire feeding the CVR.  When I test my hard-wired harnesses, I hooked up 12V directly to the input side of the mechanical (old style) CVR, and the gauges would go high very quickly (like 2-3 seconds!).  I then added the correct 10 ohm resistance between power and CVR and the gauges move nice and slowly towards high (my input signals are ground). 

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OK, that would lower the supply side voltage, but a digital regulator in series with a 10 ohm resistor will still regulate to 5v if that much voltage is still available, and I think that must be the case for the mechanical version to work. My theory is that the mechanical regulator allows the gauges to come up to their operating range quicker because of how they work.

The stock voltage regulator is a bi-metal device. A bi-metal is two dissimilar metals fused together like a sandwich into a sheet metal strip. When a bi-metal gets hot it bends because one side expands more than the other. This is very repeatable. Then they wrap it with a heater (a nichrome wire). They set the contacts to open when it gets hot, it then cools and repeats over and over. They design it to cycle on 42% of the time and off 58% of the time. That gives you about a 5 volt average over time. Its really around a 12v pulse but the gauges don't care, because they are bi-metal too and react slowly to the pulse (this dampening is inherent in the design). My guess is that when the car is started the bi-metal of the mechanical voltage regulator is on for much longer than the usual 42% of the time, because it takes time to initially heat-up. That makes the oil gauge, and the other two gauges come up to their operating range quicker. A digital regulator just applies 5v so it takes longer for the gauges to reach their operating ranges. Anyway, that's my theory. And IF the digital versions do in fact slow the time it takes the oil pressure to read correctly, then I think that's a valid reason not to use a digital regulator.

So the question is still out there- does anyone have a gauge digital voltage regulator, and does it take 30 seconds for the oil pressure to fully register? 

 

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I'll still argue for the resistor wire: as current flows through it, it heats up, adding more resistance which chokes the current and voltage down.  But...the solid state regulator should give 5V immediately regardless of input voltage fluctuations (up to a point).  Then it becomes up to the gauge to respond, which we know are rather slow to react.

The difference between no resistor wire and having one was a true eye-opener in terms of gauge response. 

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Mach1, I agree completely.  For the first few seconds, as the bimetal is heating, it applies 12 volts to the gauges.  This allows them to respond quickly.  Then the regulator starts switching on and off, creating an average of 5 volts. 

There is a way to do the same thing with a solid state regulator.  Put a capacitor on the regulator pin of a LM317, so initially it is a higher voltage output. Then as the capacitor charges, the voltage drops to 5volts.   I wonder if anyone has tried this?  Maybe I should?   Have you ever used a LM317? 

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On 7/16/2020 at 10:49 PM, danno said:

There is a way to do the same thing with a solid state regulator.  Put a capacitor on the regulator pin of a LM317, so initially it is a higher voltage output. Then as the capacitor charges, the voltage drops to 5volts.   I wonder if anyone has tried this?  Maybe I should?   Have you ever used a LM317? 

I'm sure there are several ways to get a 12v output for the initial few seconds, but before I go down that path, I'm just trying to verify if this is really a problem that has been overlooked. At the moment I don't have easy access to test anything.

Edit: 7/31/20, I have confirmation from the user of an electronic IVR (on another forum) that it takes 40 seconds for the gauges to reach their operating range, so this does appear to be a real problem, and something to consider. 

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Danno is correct I did this to my 1969.  I put a 100 ohm capacitor on input and 10 on out put and it worked fine. I never did it to speed gauges up initially tho, it's just good practice to do so to keep signal clean.  

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1 hour ago, det0326 said:

Danno is correct I did this to my 1969.  I put a 100 ohm capacitor on input and 10 on out put and it worked fine. I never did it to speed gauges up initially tho, it's just good practice to do so to keep signal clean.  

Hi Dave, I've seen anywhere from 10 to 1 mfd on the input and usually 1 on the output to keep it clean, but more will definitely still work.

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54 minutes ago, Mach1 Driver said:

Hi Dave, I've seen anywhere from 10 to 1 mfd on the input and usually 1 on the output to keep it clean, but more will definitely still work.

Yes 1 and 10 would work also but the 100 and 10 is just what I had on hand for other projects. My gauges worked really well the fuel was a little off but I think it was due to sender. I used the 7805  regulator with heat sink never gave any trouble. I talk to the guy in California  that bought my car regularly and its still working fine. Excuse please I said ohms I meant mfd I have been working on A/C motor checking resistance. Just had ohms on the brain.

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5 hours ago, det0326 said:

Excuse please I said ohms I meant mfd I have been working on A/C motor checking resistance. Just had ohms on the brain.

I knew that you knew better than that, so I didn't see any reason to mention it. Besides, ya have to give us old guys a break ;) Next time you talk to the new owner, ask him how long it takes his oil pressure to settle-in after start-up. That would settle this discussion once and for all.

Yeah that's the ticket, you need a heat sink to keep it cool. I'll bet most of the commercial versions don't have one, and that's why some people report failures. Keep it cool and within its design limits and it will last a long, long time.

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3 hours ago, det0326 said:

I'm old as dirt Terry.  73

Huh, I figured you were one of the youngsters. 

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13 hours ago, Midlife said:

Mach1Driver: have you considered putting the key to ACC for 25 seconds prior to starting the engine?  That should be time sufficient to get the gauges and CVR fully up to power.

Good point Mid, but I'm sure I would forget that step most of the time ;)

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53 minutes ago, det0326 said:

Bob, I have a son that is probable close to your age.

Wow, that's impressive Dave, I just hit 64 :)

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