SOZ Choke input filter?

[FEThead]

This a correction to my previous post. In it I said that two diodes would be conducting at any given time. That is true. But since there is a + an a - supply, each supply will be subject to only one diode drop (of about one volt per diode). SO, with 33 volts from the transformer (each side of CT), * 0.9 for the choke input filter gives us about 30 VDC ... minus one volt for the diode brings us to 29 VDC, ... after losing about 0.3 volts in the choke with the 3 amp condition, we are down to about 28.7 VDC, ... and for the 12 amp condition, we are down to about 27.7 VDC. That is per rail. You would end up with about +/- 28 to 29 VDC.

Sorry about the error.

[woody]

I am thinking of building a small SOZ with a choke input filter but
when I run the #'s for say a + - 20v supply at 4 amps it comes up
as a rather large value. In this case wouldn't an iron core inductor
be ok to use and anyone know where to get these at a reasonable cost.

Thanks

bob12345678

[gnomus]

In another thread Mr. Pass recommended the the metal core chokes at www.Zalytron.com These can saturate and the air core chokes do not. You can connect two air cores in series and the total inductance is the sum of them. Another source for air cores is www.Solen.ca

Can someone tell me what happens to a circuit when an inductor saturates? And how can you calculate the right size iron core to avoid saturation?

Thanks to all who reply.

[roddyama]

So,.. The past three days I've been looking high and low to find a way to include power supply filtering without sucking out all of the voltage. I accessed http://www.duncanamps.com/psud2/index.html and downloaded the neat little PSU analysis program (cool, I wonder if I can wear it out by using it too much). Then I went looking for inductors with high inductance and low DCR. I seen soom nice Alepha Cores made with silver foil for a bazillion dollars/oz. Then I ran across the Common Mode Chokes. Not just one or two, but at least a dozen in the US alone. It seems that they are commonly used in circuits ranging from digital data transfer filters running at uAmp levels to 3-phase line protectors operating at hundreds of Amps.

This type of choke can deliver 10's of mH with a DC resistance in the 10's of mOhm range. It appears that the common mode signal on two or more legs of a line are run through the CMC. The choke is just a coil in each line of interest wrapped around a common permeable core (often toroids). The common mode signal builds a field around the core that impedes the common mode signal in the oppossing line. Differential signals pass unimpeded.

In the power supplies, CMC are usually before the transformer in an RFI filter or line protector circuit. In the few cases I found where the CMC was after the transformer, it was before the rectification. So I thought, what if one were to wind the toroid so that the half waves coming from the bridge's + and - outputs, were seen as common mode noise. We would have an inductor of, say 40mH of inductance, and a DCR of less the 50mOhm, capable of passing 15Amps+, if it's wound with 10 or 12 gauge wire.

I tried to simulate one in Duncan's program and I could run a Transformer with 66VAC w/CT out at 28VDC @ 4amps after filtering. Then when I step the current to 8amps the voltage only drops 1V to just under 27VDC. All this with less then 3mAmps of ripple.

I made a schematic of the circuit I tried to simulate. I hope I don't screw this up as it's my first picture.

Those of you that are current in this stuff and those of you who are just generally in the know, am I barking up the wrong tree with the CMC's or am I on to something, or does Carver already have a patent on this circuit and I need to get a lawyer.

(Well, first try at downloading didn't work at 159kb)

(OK, it's 69kb, and I don't know if it got through or not. It's not in the "Preview Post". I guess that means it didn't work, but I don't know.)

(I give up. I probably have attached three files)

Thanks for the replies.

Rodd Yamashita

[woody]

I was thinking along the same lines with a ironcore inductor first
and then a air core inductor. My question is who has these common mode chokes and about how expensive are they?

Thanks

Woody

[roddyama]

Hi Woody,

Take a look at this site:

http://www.topmagnetics.com/index.htm

Look at the high current Common Mode Chokes. You'll be amazed at the simplicity of these things. It's no more then a small (<2" in dia for chokes of more then 20mH @ 5.5A) toroid core with a couple of feet of wire wrapped around it.

You could wind it yourself on a bar core, or do a search on the web for Common Mode Chokes. You'll find a lot. I'm sure it would be more then a Solen of the same value.

Good Luck,
Rodd Yamashita

[FEThead]

Bob12345678,

You said when you ran the #s on a +/- 20V, 4A PSU you came out with big numbers... What did you get? I came up with (20 V / 4000 mA = .005 Hy) 5 millihenries. Hammond Mfg makes some chokes that should work for about US $23 / ea. (You will need two: one for + and -). Go to: www.hammondmfg.com look under transformers... chokes... 159 series. I think either the 159ZJ or 159ZG will work for you. They also have others that will work, but these are a start.

As for the common mode chokes, the idea is fine but I think the ones Rodd is looking at are for the 100 to 250 KHz range where their power transformers work. (Note that these are in the switch mode PS section of their page.) I do not think they will work at 120 Hz. Unfortunately, at line freqs you need a lot of iron and copper to get a lot of inductance.

Gnomus,

When an inductor saturates it acts just like the wire it is made of. (Same DC resistance) Saturation means that the core is no longer able to absorb energy in its magnetic field. (Similar to a fully charged capacitor.) I think the TMC chokes would saturate in 120 Hz usage, but the ones from Hammond (or others with that much iron and copper) will not saturate. Air core inductors will not saturate but have less inductance per length of wire. Use them after your first L-C section with the "heavy metal" in the first section.

[FEThead]

Here is a 10 amp 10 mH choke for about $25 (plus shipping)


http://www.surplussales.com/transfor...erchklist.html


scroll down to cpw-500006001201


I have no connection to this company but I have purchased from them before and they have good stuff.

Happy listening!

[Super_BQ]

When times are tough and you can't buy - why not make your own air core inductors like the ones below?

http://www.geocities.com/super_bq/soz3.html

[FEThead]

Super_BQ

How did you wind those? Those are too neat to be hand wound. And where did you get that much enamaled wire? I have found PVC insulated wire in scrap metal yards for cheap. The selection is poor but the price is right.