Because of the high maintenance needed to monitor and filter spammers from the RF Cafe Forums, I decided that it would
be best to just archive the pages to make all the good information posted in the past available for review. It is unfortunate
that the scumbags of the world ruin an otherwise useful venue for people wanting to exchanged useful ideas and views.
It seems that the more formal social media like Facebook pretty much dominate this kind of venue anymore anyway, so if
you would like to post something on RF Cafe's
page, please do.
Below are all of the forum threads, including all
the responses to the original posts.
Post subject: Designing a transformer Posted: Thu Mar 13,
2008 8:38 pm
Joined: Thu Mar 13, 2008 8:22
I wish to build an oscillator of the
multivibrator type, for induction
heating experiments. The transformer
will be 1:1 with center-tap
on the primary. Frequency between 1khz
to 50khz. Needs to be
small as possible to fit on the PC board.
Now here's the rub;
needs to handle 115V-230V @ 1-10Amps, but should
run off as
little as 12V.
Torroids are fine, have the ARRL
Handbook 2008 and many online
L calculators but am still way over
my head. No idea what core material,
size, wire size, number of
turns, etc. Don't want to inductively heat
the transformer, just
the workpiece! Suggestions welcome, and
Post subject: multivibratorPosted: Fri
Mar 14, 2008 12:41 pm
Joined: Wed Feb 22,
2006 3:51 pm
You sure have some stringent
Start with the simple ones:
output is 115-230V@1-10 A:
230V at 10 Amps is 2300 watts, so you'll
need a big core with thick wire.
At 12V input, this is about
192 Amps - so you'll need transistors rated for at least this much current.
Likewise, at 230 V input, your transistor should be rated for at least
200 A and 500 V transistors are rare and expensive, and
need special heat sinking and drive. You're into specialist territory,
not hobbyist or experimenter territory, if I've interpreted your requirements
Post subject: Posted: Mon Mar 17, 2008 6:36 am
Joined: Fri Feb 17, 2006 12:07 pm
As Paddy once said: If I was goin thar I wouldn't start
I agree with Fred: 12V is the wrong starting point for
a system consuming more than 1kW, and using transistors is also probably
the wrong approach.
I would be thinking in terms of 56 volts at
least, and using Triacs, not transistors. The triacs would be driven
from a reliable DIL TTL or CMOS multivibrator 4047 or similar.
Also you state the transformer is 1:1 ratio, but with a primary
of 12V and a secondary of 115V or 230V, the ratio would be more like
10:1 or 20:1.
Are we missing something here?