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*To*: tesla@xxxxxxxxxx*Subject*: RE: Current Limiting and Impedence*From*: "Tesla list" <tesla@xxxxxxxxxx>*Date*: Fri, 22 Apr 2005 09:40:57 -0600*Delivered-to*: testla@pupman.com*Delivered-to*: tesla@pupman.com*Old-return-path*: <teslalist@twfpowerelectronics.com>*Resent-date*: Fri, 22 Apr 2005 09:42:46 -0600 (MDT)*Resent-from*: tesla@xxxxxxxxxx*Resent-message-id*: <1wdq_B.A.iqB.1tRaCB@poodle>*Resent-sender*: tesla-request@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 > >

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