Hmm, Where you measuring with respect to ground or across the coil?

 

OK. You asked for this in a PM.
I have stayed out of this because ronv and Alec t seem to be way ahead of me.

The way I see this is that you need to inflict a DC voltage at the start to get the current to ramp up in the rate you measured. 8.44 amps in 450 useconds through 1.1 millihenry is a known calculation.

1V/1H = 1A/1S
V = .0011H x 8.44A/ .00045 seconds
V= 20.63

Then hold at 12V for a time duration that is dictated by the needs of the rest of the system for that valve to stay open. Shut off quickly and 3.375 amps in 1.1 millihhenry makes energy = 1/2 LI^2

1/2 .0011H 3.375A squared is .00626 energy somethings
.00626 = 1/2 CV^2
.0125 = C 75V^2
.0125/5625 = C
2.2uf = C

These numbers seem to indicate that you need a 20 volt supply and the rebound energy is absorbed by a 2.2 uf capacitor. I did not calculate for DC resistance because I don't know how.

.62 ohms times 8.44 amps will add about 5.2 volts to the 20.6 initial voltage??
12 volts/.62 ohms would carry 19.35 amps during the, "hold" time so my numbers seem wrong. That's why I stayed out of this. I might have given you an idea but I didn't give you any hard numbers.

 

I might have given you an idea but I didn't give you any hard numbers.

Any clue that brings me closer to solving this problem is thoroughly appreciated... thanks

 

Hmm, Where you measuring with respect to ground or across the coil?

Across the coil

 

I'm still trying to figure out how there is only 3.8 amps with 12 volts across the coil.

 

I guess I did contribute something. ronv landed exactly on my worst doubt.

 

I guess I did contribute something. ronv landed exactly on my worst doubt.

Not just a pretty face.

 

I'm still trying to figure out how there is only 3.8 amps with 12 volts across the coil.

I'm going to double check on that, I had a Lab that owns me a favor test it for me, so I wasn't there when it happened.

 

Here's a recalculation on the wire:

24 ga "heavy film coated" meets the measured size exactly.
that's 25.67 ohms per 1000 ft.
Mean radius is 1.16 inches
mean circumference is 7.326 inches
100 turns is 728.8 inches
which is 60.7333 ft
times 0.02567ohms is 1.56 ohms.
12V/ 1.56 ohms is 7.7 amps
Not a lot of difference compared to 3.8 amps.

If your measurement was for naked wire, that's 23 ga at 49.26 ft/ ohm or 0.0202 ohms per foot
and that's 1.233 ohms allowing 9.7 amps.

Something is very wrong.

 

Not just a pretty face.

Not as pretty as joeyd999

 

Not as pretty as joeyd999

Now that ain't fair... not all of us were born with his looks...

 

I had to wait a long time before that kind of beauty accumulated.

 

Here's a recalculation on the wire:

24 ga "heavy film coated" meets the measured size exactly.
that's 25.67 ohms per 1000 ft.
Mean radius is 1.16 inches
mean circumference is 7.326 inches
100 turns is 728.8 inches
which is 60.7333 ft
times 0.02567ohms is 1.56 ohms.
12V/ 1.56 ohms is 7.7 amps
Not a lot of difference compared to 3.8 amps.

If your measurement was for naked wire, that's 23 ga at 49.26 ft/ ohm or 0.0202 ohms per foot
and that's 1.233 ohms allowing 9.7 amps.

Something is very wrong.

Actually, I did measure the wire diameter with a caliper (after destroying a sample using a mill), and it matches exactly that of 23 ga light film coated (0.0235"Ø @ 0.02031Ω/foot) given in page 9 of this document. If you look at post #1, I calculated 30.53 ft total from the coil's geometry that I also carefully measured (it has a mean diameter of 1.166" and a height of 0.470", and I also physically counted the number of turns), and it also matches exactly the resistance value of 0.62Ω that I measured. That's 0.02031Ω/foot X 30.53 = 0.6200643Ω
As for the way they measured the inductance... now I'm having second thoughts. I called the Lab and they told me they'll get back to me on that one.... so I'll post it here as soon as they let me know.
Why is that important? I mean, they used professional equipment to measure the inductance. Would the given value change depending on whether they measured it using a sinusoid of ±1 V with respect to ground or across the coil?

 

Yes, inductors change inductance with frequency. It depends a lot on the core, and a solenoid is a moving core.
They also fail at high frequencies because of internal capacitance, but that's usually in the MHz range.
Wouldn't this be so much easier if you had one of those valves to plug some voltage into?

 

Yes, inductors change inductance with frequency. It depends a lot on the core, and a solenoid is a moving core.
They also fail at high frequencies because of internal capacitance, but that's usually in the MHz range.
Wouldn't this be so much easier if you had one of those valves to plug some voltage into?

Well... yes, I do have one of those valves available. Are you suggesting I approach this thing starting with an educated guess, and then proceed with trial and error?

 

I guess I'm assuming you can measure the resistance and inductance if you have all day to do it. I think you still need to go re-run the voltage and current checks that somebody botched.

 

I guess I'm assuming you can measure the resistance and inductance if you have all day to do it. I think you still need to go re-run the voltage and current checks that somebody botched.

Well, if somebody botched something, then that would be me..
Anyway, the voltage is something that I'm 100% sure of, since the waveform shown is something I've measured 100s of times before. The current waveform is something that I've measured only once, using a AMP25 amplock sensor, that has a 37mV/A sensitivity. I've attached the original scope image for you to see, settings and all.

EDIT: The AMP25 works at 5V, and has a 2.5V offset, that's why I couldn't bring it's waveform down all the way to the center of the display.

 

Ahh, I think I see it. The voltage isn't exactly on ground to start with - maybe 10 volts. Then this would fit pretty well.

 

Ahh, I think I see it. The voltage isn't exactly on ground to start with - maybe 10 volts. Then this would fit pretty well.

Would you mind clarifying? My knowledge of analog electronics is quite limited.

 

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