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Re: Current Limiting and Impedence

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

Hi Malcolm,

My CRC chemistry and physics book shows the following properties of silicon iron:

mu = 500 @ 20 gauss
mu_max = 7000
Bsat = 19700 gauss
Wh = 3500 ergs/cm^2  @ saturation (hysteresis loss)

Interesting to compare to insulated powder - 2-81 permalloy (I assume your N27 ferrites are in this catagory???)

mu = 125 @ 20 gauss
mu_max = 130
Bsat = 8000 gauss
Wh = --- don't know what this means, maybe negligible and if so => little or no core loss??

The smaller mu might be good if one wants a small inductance but the lower B saturation may mean larger core area.

It looks like purified iron may even be a better choice than silicon iron much higher mu, about the same saturation point, and very low core loss. Don't know anything about availability or cost.

Any comments???  and/or more info about N27 ferrites

Gerry R



Original poster: "Paul B. Brodie" <pbbrodie@xxxxxxxxxxxxx>

Malcolm,
You mention N27 ferrites but the ferrites I have access to are surplus and completely unmarked and of unknown origin. The good thing is that I have a bucketload of them that have accumulated from various sources over many years. I believe that most of them are ferrite beads that were on power cords. Would these work in use as you suggested, crushed up in a PVC tube? I like this idea as I have ready access to so many ferrite beads. Since it sounds so good, I just know you are going to tell me that they are completely different from the ferrite used for toroids and transformers and therefore useless for this application. {:-(
Regards.
Paul
Think Positive

----- Original Message -----
From: "Tesla list" <<mailto:tesla@xxxxxxxxxx>tesla@xxxxxxxxxx>
To: <<mailto:tesla@xxxxxxxxxx>tesla@xxxxxxxxxx>
Sent: Thursday, May 12, 2005 4:46 PM
Subject: Re: Current Limiting and Impedence

> Original poster: "Malcolm Watts"
<<mailto:m.j.watts@xxxxxxxxxxxx>m.j.watts@xxxxxxxxxxxx>
>
> On 12 May 2005, at 10:27, Tesla list wrote:
>
> > Original poster: "Gerald  Reynolds"
<<mailto:gerryreynolds@xxxxxxxxxxxxx>gerryreynolds@xxxxxxxxxxxxx>
> >
> > Hi Malcolm,
> >
> > Where can you get Silicon steel?? Do they make welding rods out of
> > this stuff or is there another alloy that would work?? and what
> > diameter rod should we be looking for??
> >
> > Gerry R.
>
> Hi Gerry,
>           Silicon steel is the material used in transformer
> laminations. I can't suggest any shortcuts to getting it any other
> way sorry. I'm suggesting making the core using discarded transformer
> laminations. You just want whatever material you are using to have as
> small a cross-sectional area as small possible to minimize eddy
> currents. A tale was recounted some years ago of someone who made a
> ballast core from varnished welding rods which got so hot that the
> varnish melted. It is questionable whether low-frequency type
> transformer iron is really that suited to the job anyway as the gap
> is going to throw step functions at it. A PVC tube full of smashed up
> N27 ferrites would be a better option. I did this once and built two
> such cores.
>
> Malcolm
>
>
>
> >
> > >Original poster: "Malcolm Watts"
<<mailto:m.j.watts@xxxxxxxxxxxx>m.j.watts@xxxxxxxxxxxx>
> > >
> > >Hi Paul,
> > >           Whatever rods you purchase for the core, they have to have
> > >a very small x-sectional area. They should also not retain much if
> > >any magnetism after being de-energized (check with a magnet) or they
> > >will have large hysteresis losses resulting in lots of heating.
> > >Silicon steel such as used in transformer cores is preferred if you
> > >can get them.
> > >
> > >Malcolm
> >
> >
> >
> >
> >
>
>