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microwave transformers

 * Carbons Sent to: usa-tesla-at-usa-dot-net

Quoting P.L.Mason-at-bath.ac.uk:

> I have got a couple of 2.5kV (unloaded) microwave oven 
> transformers lying about and I am keen to rig them up as a 
> decent TC supply. I was running through some of the old 
> postings and found that someone had recommended connecting 
> these up using a Cockroft-Walton doubler. Is there any way that
> I can avoid this and still get decent results with minimal 
> agro?  (I am hoping to get my hands on a couple more fairly 
> soon).  Cheers  Phil Mason

Phil:

One side of the HV winding on these are typically grounded to the
core. For wiring two of these transformers together you simply
ground the cores, put the primaries in parallel, and you end up
with two hot secondary terminals. The secondary winding is of
course center tap grounded, which means you ground to your RF
ground. Mind your phasing.

Four of these transformers can be connected in series, but you
must pay close attention to phasing and grounding. Since one side
of the secondary is typically grounded to the core, two cores
will have to be hot, and two cores will be grounded. The hot
cores need to be the better insulated of the lot if you have a
choice. If you have transformers with different voltage ratings,
ground the core of the lower voltage rated, this reduces the
voltage stress on the two hot cores.

The only problem with this arrangement is the possiblity of
having HV arc from the hot core to the lower voltage primary
winding. Check and double check the construction to make sure
there are no flaws in the insulation of the hot core units.
Several coats of polyurethane, epoxy, or two-part polyester may
be used to build up an additional layer of insulation between the
core and the primary winding. Submerging the hot core units in
oil is also a definate possiblity.

Given the difficulty of securing neon sign transformers in your
part of the world, it might be a good idea to work out something
using components that are typically available in the UK. I hear a
lot of complaints from coilers in other parts of the world who
have access to lots of microwave parts but rarely see a neon
sign.

Richard Quick


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