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Re: Transformer Questions
Hi Mike,
The cores you have should be good for about 2,500 watts (continuous).
Trying to get more, out of nine square inches of iron, cross section, is
probably asking for problems. (at 60 HZ; raise the frequency, and you
might stand a chance)
See> http://members.tripod-dot-com/~schematics/xform/xformer3.htm
The type of core you are talking about sounds like a tape-wound core. A
steel band is wound on a (usually square or rectangular) mandrel and
bound with adhesives. The ring of metal is removed from the mandrel and
cut into two halves, which are then polished and sometimes etched with
acid to undercut the ends slightly to prevent eddy currents where the
machining took place.
It is very important to keep the matched halves together, and to keep
each leg facing its own mate. If you mix them up, it is usually easy to
see where they are supposed to go, by looking at the coloring at the
edges of the laminations.
This type of core is very sensitive to dirt inadvertently trapped in the
gap. A small speck of material, can cause a great loss in inductance.
Tape wound transformers, are only exceeded in efficiency, by continuous
wound toroidal transformer cores. (assuming 60 HZ power applications)
The stainless steel clamp you intend to use, should work very well.
Because you are winding a high voltage transformer, you will probably
want to wind the secondary on an opposite part of the core from the
primary, rather than directly over it. This greatly simplifies
insulation requirements, and improves cooling. In TC operation, there
will be less electrostaticly conducted interference from one halve to
the other. You will sacrifice some efficiency doing it that way (higher
leakage inductance) but considering the benefits, it's a good
compromise.
Core length affects the amount of leakage inductance. (reluctance is a
magnetic property of the steel) Shorter is better, as a general rule,
but for a TC application, the added leakage will make ballasting less
critical. It is typical, with this type of core, to put the windings
over the gaps. This tends to lower leakage inductance.
No idea what they might be worth, but you can bet they would cost a
great deal more than loose laminations of the same quantity and quality.
Hope that helps
Take care
bob misiura
Tesla List wrote:
>
> Original Poster: "Mad Mike" <mglass-at-netusa1-dot-net>
>
> Hi all
> I need the advice of a transformer guru. I have recently aquired 4
> transformer cores which have a short U and a long U with ground surfaces to
> mate the two halves together. They were originally held together with 2 SS
> bands and a crimp. I plan to hold them together with a pair of SS hose
> clamps. The "window" is 7 1/4" x 2 3/4". the legs are 1 3/4" x 2 1/2". Each
> unit weighs about 30 lbs. I've run the numbers through the formulas and my
> plan is to wind 2 transformers of 15kv (2 - 7500 vac windings in series) -at-
> 2500 watts each then run the two units in parallel for 5000 watts total.
> (I'm using
> #10 wire for the primaries and #30 wire for the secondaries). Some
> questions: Most cores I have seen are fairly square, these are pretty long,
> will reluctance be a problem? What would be the best setup for TC use, the
> primary on one leg and the secondaries on the other or a primary and a
> secondary on each leg? The transformers will of course be run in transformer
> oil, how much wattage could one safely wring out of this design beyond 5000
> watts? As to the cores themselves, what would they cost if I didn't have a
> free source? Any input is welcomed.
> Thanks
> Mike KB9NZQ