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RE: [TCML] 7.5V 52A Filament Transformer for 3CX3000 Needed
Hi Cameron,
Unless you need high voltage isolation, a well made, modified DIY
transformer will meet or exceed a commercial transformer for ratings. As has
been already stated, in rush is an issue - a variac is the way to go as it
can ramp up the voltage slowly. It has been suggested by Dr. Spark and as a
rule of radio amateurs and others that running filaments or in this case a
quad, 833c for instance, at 500mv (exacting) above 10V prolongs filament
life and improves the efficiency of boiling off the electrons off the
cathode.
Save your money and buy some good meters and a dedicated variac. A NST makes
a very good platform for heavy wire wound secondary's and will run 24/7
without braking a sweat or getting warm. I don't care for MOTS as the
primary number of turns suck and gets hot as a result. It is simply a matter
of VA, turns ratio, core area, suffiecint turns/volt on the primary, and
awg# selection for the output current. With 20 or 30 amps to spare, leakage
and such is not much of an issue. Just make sure the windings are secure. A
good practice is to drive wood wedges under the windings to assist cooling
and keep things solid. We are, after all, "coilers".
I'll post a picture of mine shortly. It can deliver at least 60amps without
voltage droop. As opposed to Hank view, point well taken, (assuming you use
a variac)I like head room as long as you bring up the voltage slowly and the
voltage needs to be very precise. On the hairy edge won't provide for that.
See Dr. Sparks video on the subject with his quad. He is using a pro job
that is actually a 12v transformer.
Jim Mora
-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On Behalf
Of Cameron B. Prince
Sent: Sunday, June 14, 2009 12:30 AM
To: Tesla Coil Mailing List
Subject: Re: [TCML] 7.5V 52A Filament Transformer for 3CX3000 Needed
On 6/12/09 6:21 PM, "Dr.Hankenstein" <dr.hankenstein@xxxxxxxxxxxxx> wrote:
> Normally, filament xfmrs should be chosen to approximate the max load.
> The reasoning behind this is as follows:
>
> Filament resistance is very low at start up, thus causing heavy inrush
> current that could damage the filament.
>
> By closely matching the xfmr impedance to the filaments' maximum
> operating current, the inrush can be greatly reduced, resulting in
> longer filament (and tube)life.
This, along with my desire to build something of high quality, is precisely
why I'd rather not go with the "homebrew" method. I should have prefaced my
original request with the requirement that any replies be related to
commercially built transformers running at their rated input voltages
designed for the specific application mentioned.
Money is always an object, but in this case, I'd rather pay for the proper
transformer and be safe rather than sorry.
Thanks,
Cameron
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