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RE: Current Limiting and Impedence
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- Subject: RE: Current Limiting and Impedence
- From: "Tesla list" <tesla@xxxxxxxxxx>
- Date: Fri, 22 Apr 2005 09:40:57 -0600
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Original poster: "Mark Dunn" <mdunn@xxxxxxxxxxxx>
You may be onto something.
My current limiter is homemade from a pair of U100/57/25 U-Cores. They
were salvaged so I don't know the exact matl, but based on the mfg
markings I believe that the max AL = 5500 nH.
Ae = 645 mm^2, Le = 308 mm
My coil is 160 turns of #14 ga coated magnet wire.
I don't have my notes with me, but I recall that ungapped it has ~ 60 mH
I currently run with a gap(I think .015" - have to check notes at
home)and an Inductance L = 15 mH.
So my inductance per turn is 596 nH which is below AL = 5500 nH so
that's OK, BUT I get:
Core Flux = 810 uWebers
Core Flux Density = 1.26 Tesla
Based on what I know, 0.5 Tesla is saturation and I should design no
higher than .32 Tesla.
If yes, I need more core volume, right?
I just computed a solution with more turns - appears 600 turns would get
me down to .32 Tesla, but I'll need a .75" air gap to get the L = 15 mH
I need. Seems I really screwed this up.
Am I really this far off? Sorry to pester you guys with this simple EE
stuff, but sometimes I get myself confused and don't have anyone to
discuss concepts like this with.
Original poster: "Gerald Reynolds" <gerryreynolds@xxxxxxxxxxxxx>
Hi Terry and Mark,
Something sounds backwards to me on this. If I understand correctly,
90 Vac is across the transformer and not the ballast inductior. I'm
thinking the ballast inductor is saturating.
>Original poster: Terry Fritz <teslalist@xxxxxxxxxxxxxxxxxxxxxxx>
>Here is my shot on this one...
>At 06:22 AM 4/21/2005, you wrote:
>>Please follow my math and explain my confusion.
>>My TC power transformers have an impedence Z = 1.2 Ohms(secondary
>Ok, so if the output is a dead short, you draw 100 amps. Too high ;-)
>think you are using microwave transformers if I remember right.
>>I built a Current Limiting Inductor(CLI) with L = 15 mH, thus at 60Hz
>> X = 2*Pi*60*.015 = 5.65 Ohms. The R for the CLI is negligible. So
>>the inductor Z = 5.65 Ohms. The system therefore has total impedence
>>of Z = 5.65 + 1.2 = 6.85 Ohms.
>It might be more like SQRT (5.65^2 + 1.2^2) = 5.77 ohms. But close
>>This limits current to 120 VAC/6.85 Ohms = 17.5 amps.
>>I have confirmed this through testing.
>Ok perfect!! The coil does not always run into a dead short so a 15
>circuit should be fine. I suppose you could even sneak by with less
>inductance in that case, but best to start out real safe.
>>Measuring voltage BETWEEN the inductor and transformer I get around 90
>>to 100 volts(Mains 120V). So if I break down the circuit and consider
>>the current the individual components... Transformer I = 90 VAC /1.2
>>ohms = 75 amps
>>CLI I = 30 VAC /5.65 Ohms = 5.3 amps
>That's almost right. It is like a voltage divider. 120 x 5.65 / (5.65
>1.2) = 99 volts
>120 x 5.77 / (5.77 + 1.2) = 99 volts too.
>The current is the same in both the inductor and the transformer. I
>you got the voltages backwards... It is the voltage across the device
>divided buy the resistance.
>30/1.2 = 25 amps
>90/5.65 = 16 amps
>Probably some significant phase angle error now in this case.
>>Obviously, one can't analyze the components this way. Is it because
>>the voltage measurements are not accurate due to the phase angle? Am
>>I not allowed to analyze individual component impedence? What don't I
>I think you just got a little confused. It all seems right to me.
>BTW - Here is a $30 meter that can measure real power and power factor.
>But don't overload it too much. No relation to "me" even though they
>my test report with permission.