[Prev][Next][Index][Thread]

More HBT info for Doug



 Original Poster: Doug Brunner <dabrunner-at-earthlink-dot-net> 

 Question: what do you mean by "shunted" and "non shunted"?

Hi Doug,

The difference between a shunted and a non shunted tranny is very simple. The
non shunted just has a simple iron core. Usually they are a mix of Eīs and
Iīs, altho there are different shapes out there. My xformer core (I plan to
use for my HBT) is made of two Eīs, one being backward. One outer leg of each
E is shorter and the middle leg is cut at an angle, so they fit nicely front
to front to form the core. The lamination of the core (instead of just a chunk
of iron) reduce the eddy current losses in the core (considerably).

A shunted xformer has a set of laminations inserted 90° to the real core. This
limits the magnetic flux that can pass through the core, limiting the max
current. If you short one of these transformers the voltage breaks down and
the current can only go as high as the shunt (90° lams) allows it to go. This
transformer can be shorted all day and night without harm. The reason NSTīs
are limited in this manner is very easy to explain. The neon tube has a
positiv U/I curve. This means the more volts you put put in, the higher the
current will go. If the NST werenīt current limited either the tube or the
tranny would go up in smoke. The neon tube only needs the 15000 volts to
ionize the gas, so that it can start to conduct. After that the NSTīs voltage
breaks down to about 600-1kV.

Get the "real" (iron core) NST before they die out and start to get really
expensive.

For this reason newer signs are starting to use a semiconductor xformer. They
ionize the gas per thyristor kick and (after the sign is started) they run a
frequency controlled switching psu providing the necessary 600-1000 volts to
keep the sign lit up. They are frequency controlled for two reasons:

1.) A HF PSU is smaller and cheaper to build.
2.) A change in frequency changes the output voltage. Voila, you now have a
dimmable neon sign !! (Which in do course lets the companies charge more for
something that is cheaper to build. But itīs got any "extra", so the end
customer has to pay more for it.)

You can look at the magnetic shunt like a series (with the primary winding)
inductor which some of us Teslanians use externally on pole pigs or other non
current limited xformers. If you short a pig it will either burn out and pull
your whole neigherhood down in the process or your circuit breakers
(hopefully) will cut out. A 10kVA pig is NOT limited (talking about max input
amps here) to 10KVA!!

I have to agree with Malcom about your core going into saturation without even
getting near your 120 volt input. To make a wild guess I would say your core
will saturate somewhere between 35-60 volts. This means if you go above this
voltage you are not going to get an incease in your output voltage thatīs
anywhere near being linear. Actually an increase in input volts wonīt be
noticeable in your output. 
The "extra" energy will just be wasted in core/wire heating. Nothing you
really want, building a xformer.

If I were you I would seriously think about using larger wire gauges and only
one wire (instead of 5). The larger wire size isnīt going to be more expensive
than five times the smaller diameter length. If this WAS the way to go, donīt
you think transformer makers would do this?

 As someone else stated a while ago there is no black magic in winding
transformers. There is a good deal of know how behind the core construction,
but the winding just boils down to cost effectiveness, which is something to
consider when you are making thousands of xformers, but when you are just
winding one or two.

My advice is if really, absolutely, must want, have to do, go your way then
take Erikīs advice and start with the primary. Wind it. Take a variac and an
ampere meter and measure the current as you ramp up the voltage. Iīm sure you
WILL then see why itīs not the way to go.

Coiler greets and good luck from germany,
Reinhard