RE: Current Limiting and Impedence

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Mark Dunn" <mdunn@xxxxxxxxxxxx>


Gerry:

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
inductance.

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.

You agree?
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.

Thanks
Mark





Original poster: "Gerald  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>

Hi Terry and Mark,

Something sounds backwards to me on this.  If I understand correctly,
the
90 Vac is across the transformer and not the ballast inductior.  I'm
thinking the ballast inductor is saturating.

Gerry R.


>Original poster: Terry Fritz <teslalist@xxxxxxxxxxxxxxxxxxxxxxx>
>
>Hi Mark,
>
>Here is my shot on this one...
>
>At 06:22 AM 4/21/2005, you wrote:
>
>>All:
>>
>>Please follow my math and explain my confusion.
>>
>>My TC power transformers have an impedence Z = 1.2 Ohms(secondary
>>shorted).
>
>Ok, so if the output is a dead short, you draw 100 amps.  Too high ;-)

>I
>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
>enough....
>
>
>>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
>amp
>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
>think
>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

>>understand.
>
>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.
>
>http://www.themeterguy.com/advertising/Kill%20A%20Watt/killawatt.htm
>
>But don't overload it too much.  No relation to "me" even though they
>use
>my test report with permission.
>
>Cheers,
>
>         Terry
>
>
>
>
>>Thanks.
>>Mark
>
>