inductor sizing

There once was a fellow named John, Who happened to argue with John. The problem was this, When it came time to piss, It was John vs. John vs. john.

Cheers! Rich

Twit.

I gave the op a couple of tips. JF, while providing no help at all, chose to rag me for insufficient something or other.

He's mildly annoying, but not especially good at that, either.

John

Nope.. That was for Jamie's H bridge circuit.. He started this thread. I mentioned an F mix ferrite inductor as an example that it can't handle the current. Another core material is needed. I popped that in while I was already looking at the data sheet for my project.. I'm on post entitled Smps Ferrites, frequency and loss. I'm currently poking around with core volumes and rate of rise from a loss density of 300 mW/cm^3.

D from BC British Columbia Canada.

Thanks John, I appreciate your info! :) John Fields poetry is pretty good too, I think he might like you.

cheers, Jamie

Hi Harry,

The X axis units are incorrect, the actual frequency of the sine wave is

60Hz. The square wave is actually PWM its just the frequency (200kHz) is too high to see on the display so it looks like a square wave.

cheers, Jamie

>

Tom Bruhns is correct in that it should be a 4 pole (LCLC) filter to keep the parts in obtainable sizes. This output filter will have little effect on the THD of the 60Hz output but is needed to attenuate the 200KHz carrier. So select your corner frequency, maybe around 25Khz, and part values, as TB points out, (5uH, 10uF, 20uH, 1.0uF) and then the inductors can be designed. To minimize size, try to make the volume of the caps equal to the volume of the inductors. For caps use polypropylene. Cheers, Harry

On Mar 6, 9:26 am, "Harry Dellamano" wrote: ...

After I posted that yesterday, I did a quick calc to see how big an AIR CORE solenoid coil of 8AWG wire might be, to yield 5uH. Of course, the 8AWG should be Litz wire made from perhaps 40 strands of

24AWG enameled. But 5uH is only about 15 turns in a single-layer solenoid 1.5 inches ID. You could certainly do better making it three layers of 5 (or less) turns each, but I don't have a handy multi-layer inductance calculator (I normally do RF work...). With air core, it will NEVER saturate. Stack a few toroids to use as a rod to wind it around and you can get by with a few less turns even; it's still got a huge air gap in the magnetic path, so saturation again isn't a problem. Avoid closed-loop cores (but beware of field leakage then).

Cheers, Tom

Hi Jamie

I think Toms right,

I've recently worked on a similar inverter operating at up to 5kVA

115Vac 400Hz. For the output filter we used two 60uH inductors in series and a 20uF polyprop capacitor. However, we used IGBT's switching at around 25kHz. We did/still have some stability issues but managed to achieve around 2% THD at 2.5kVA load.

For the inductors we used ferrite E55 cores with a large gap and foil windings. I did briefly look into using iron power and MPP toriodal cores but did'nt see any benefit.

I not sure it will be practical to switch at 200kHz at this power level but you don't need anything like 250uH.

Mark

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Thanks! :-)

I thought the purpose of MPP (and similar) was to act like gapped ferrite. It's a distributed gap.

D from BC British Columbia Canada.

5uH is kind of small. The first C will have to eat most of the 200KHz ripple current passing thru the first inductor. A cap array, 4x2.2uF/400V (high current polypropylene) will handle 10Arms so the ripple current in the first L is 10Arms or about 35App, so L=TE/I = E/2*F*I = 440/2*200k*35 = 31uH. The second stage gets some of the ripple current so I would start at 25uH and SPICE to get all the DC, RMS and AC current values for all L+Cs. Avoid open-loop cores, this is serious flux here, impossible to shield. At this frequency we are talking power ferrite material in a closed magnetic path with a good size shielded gap. YMMV Harry

Mark has it correct, MPP or Iron Power will get eaten alive with core losses at 200KHz. Power ferrite material is the way to go but Foil windings sound very bad. They are composed of many layers and proximity losses will be large. Litz wire, on maybe

I have your LCLC filter designed with all part numbers. I will sell it to you for a bottle of tequila. What say you? Harry

I gladly admit errors. I seldom agree with you on what actually is an error.

And you call "bobbing and weaving" with what I call "having ideas."

Oh, what the hell does "bobbing and weaving" actually mean?

John

Is there some basic theory behind keeping the volumes equal?

I wonder if it would help to kill the 200 KHz with an initial resonant LC, and then use a smaller LC to kill the harmonics.

John

Sounds like a deal as long as you promise not to drink it all in one night :)

Just tell me where to send and your favorite type!

cheers, Jamie

Not speaking for anyone but myself. I seemed clear to me that there was a recommendation for ferrite and gapped ferrites. "tend to burn" is significant.

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Clever. :-)