inductor sizing

[whit3rd]

F type ferrite from Magnetics Inc starts into saturation around 1/2
oersteds.
You can't even get 1 turn on it with 30 amps DC!

Cuk converter was the issue, right? There's no 30A DC anywhere
there. It's only primary current *turns minus resonant secondary-
current
*turns that has to be below saturation. If the primary current
is cancelling the secondary current, each can be in the 80A
range with no problem.

Don't do the calculation if you don't need the answer...

 

[Rich Grise]

Stick to designing 555 circuits; your career as a poet doesn't look
promising.

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

 

[John Larkin]

Twit.

 

[John Larkin]

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

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

 

[Jamie Morken]

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.

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

cheers,
Jamie

 

[Jamie Morken]

Jamie,
Your Vout + PWM waveforms confuse me. The frequency of the output and
PWM is about 0.35Hz. There is no PWM just a square wave and the filtered
output is shifted 0 or 360d and at that amplitude and phase cannot be
the filtered output.
Please advise,
Harry

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

 

[Harry Dellamano]

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

 

[Tom Bruhns]

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

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

 

[John Fields]

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.

 

[John Fields]

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

 

[John Larkin]

You'd probably be happier in one of those newsgroups devoted to
amateur psychoanalysis and human potential and stuff like that. This
group is about electronic design.

John

 

[John Larkin]

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.

The cheap yellow paint that Micrometals uses smells terrible when it
burns.

John

 

[John Popelish]

The cheap yellow paint that Micrometals uses smells terrible when it
burns.

Its not paint. It's a long distance, over-temperature
indicator.

 

[John Fields]

You'd probably be happier in one of those newsgroups devoted to
amateur psychoanalysis and human potential and stuff like that. This
group is about electronic design.

---
LOL, really????

What, have you run out of recipes and anecdotes about beans and
pictures of the environs of SF and your building and restaurant
recommendations and on and on and on?

 

[Harry Dellamano]

"John Larkin" > wrote in message

Is there some basic theory behind keeping the volumes equal?

Not to my knowledge, the OP started with 250uH which would have resulted
into a large filter so I was just trying to point out that a smaller total
size is optimum. I suppose you could make the same argument for minimum
cost.

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

Interesting, because of the PWM and duty>90%, there are a ton of harmonics.
To do a good job attenuating the first harmonic the smaller LC would have to
start early so the fundamental trap may not be too effective. Do not quote
me on this!
Cheers,
Harry

 

[John Larkin]

---
LOL, really????

What, have you run out of recipes and anecdotes about beans and
pictures of the environs of SF and your building and restaurant
recommendations and on and on and on?

Why would I run out of things? I keep doing things.

Last night we went to a restaurant decorated with - almost
counstructed from - electrical conduit. I discovered Little Gem
lettuce, truly superb with their dressing, with roasted hazelnuts and
radish slices.

In the Mission District, the dining philosophy is to grab any parking
spot that may magically appear, and then walk into the closest
restaurant.

http://www.sfbg.com/entry.php?entry...d=317&issue_id=342&volume_num=42&issue_num=23


John

 

[John Larkin]

"John Larkin" > wrote in message

Not to my knowledge, the OP started with 250uH which would have resulted
into a large filter so I was just trying to point out that a smaller total
size is optimum. I suppose you could make the same argument for minimum
cost.
Interesting, because of the PWM and duty>90%, there are a ton of harmonics.
To do a good job attenuating the first harmonic the smaller LC would have to
start early so the fundamental trap may not be too effective. Do not quote
me on this!
Cheers,
Harry

Good point. PWM does complicate the harmonics situation.

Incidentally, if one does a 2-stage filter, the cheap iron powder
cores are usually fine for the second stage.

John

 

[Harry Dellamano]

Good point. PWM does complicate the harmonics situation.

Incidentally, if one does a 2-stage filter, the cheap iron powder
cores are usually fine for the second stage.

John

Excellent point, the second inductor has very little 200KHz causing core
loss, so 60Hz material, with higher flux density would be suitable. Litz
wire is also not needed but parasitic capacity should be reduced as much as
possible.
Cheers,
Harry

 

[John Fields]

Why would I run out of things? I keep doing things.

Last night we went to a restaurant decorated with - almost
counstructed from - electrical conduit. I discovered Little Gem
lettuce, truly superb with their dressing, with roasted hazelnuts and
radish slices.

In the Mission District, the dining philosophy is to grab any parking
spot that may magically appear, and then walk into the closest
restaurant.

http://www.sfbg.com/entry.php?entry...d=317&issue_id=342&volume_num=42&issue_num=23

---
Geez, I guess that since, according to you,

"This group is about electronic design."

What's good for the goose isn't good for the gander?"

 

[John Larkin]

---
Geez, I guess that since, according to you,

"This group is about electronic design."

What's good for the goose isn't good for the gander?"

Gosh, you sure have a way with cliches.

John