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Tips on optimizing induction heaters
In a message dated 96-04-13 11:21:15 EDT, you write:
>Although I can't say that I am entirely happy with my Scientific Systems
>inductive heater, (13mm is the largewst electrode you can use, and it is a
>bit slower than others I've used -about 40 sec's to heat to cherry, vs. 4
>sec's with one Jake had) but even when ordered with an extra coil (since
>they are solid rings one goes on before the tubulation is connected) it was
>only 200 (or 250). And although I may not be perfectly happy with the unit,
>I was very happy about not paying 3000.
>Morgan
Morgan, with every induction heating device, there is a period of initial
optimizing of your induction heating coils, which usually improved the
performance of mine when I started out. You should try to make some different
coils with various numbers of turns, diameters, etc. In case you haven't done
this yet, wind them out of 3/16" refrigeration copper tubing on a mandrel of
any sort. You can make one large enough in diameter, at very least, to be
able to accomodate the larger diameter electrodes beyond the 13mm which is
your current max. I usually have one large coil just for those situations
where I want to stick both electrodes in the coil at once, where they are
parallel to each other and close. With 7mm electrodes, I had to really
optimize more, since they are so tiny. The cross section of the electrodes
has a lot to do with the RF energy they intercept. This will take a little
time but in the end you will discover one that is working significantly
better. I found with my system, I had to increase the number of turns much
more and make the diameter of the coil smaller to get the best performance
for 7mm. I use water cooling in the tubing, and this seems to keep the glass
of the electrodes heat sunk to prevent their cracking. But try not to let the
glass actually touch the cold coil if you can avoid it, since this may
occasionally result it extremely small stress fractures around the electrode,
visible only at the highest vacua. When I have mica in an electrode, I find
it works best removing this, since it is really unnecessary and not very
clean as a vacuum material, slows down the process significantly. I can see
this very clearly in the time it takes me to bombard and my vacuum to
recover. There's a very significant speed improvement using Eurocom RP
electrodes this way, and this is what I always use for anything 12mm and
above. Strangely, Masonlite was the worst for some reason for this special
type of bombarding, it took forever to recover the vacuum, sometimes an hour
or more. And don't forget that if you have some vacuum failure such as a
leak, you won't get any visible heating since it depends on the insulating
properties of a vacuum to build up heat, but you probably knew that already.
In case of very small electrodes, I have to sometimes turn up the gain on my
heater to the point where it is not good to leave it run for more than 30
seconds at a time, so I can cycle it. Seems for the 7mm ones, sometimes
there's a threshold effect sometimes where you have to hit it hard to start
it, perhaps to blast off an oxide coating on the outer jacket ?
Good Luck!
Jeff Golin