Hi Rob,
I don't mean to be a "wet blanket" to your enthusiasm
over building a major league sized high powered Tesla
coil withe that x-ray transformer (from what you wrote
I assume that you are the purchaser of that unit), but
running a 50 kV primary circuit voltage coil will indeed
present some formitable challenges that are not typically
encountered with coils using more modest primary volt-
ages, say in the 10 to 20 kV range. Scot - aka bunnykiller,
can tell you first hand how much of a challenge voltage
standoff is in the primary tank circuit with just ~30 kV,
as he has piggy-backed two 14.4 kV pigs (pun intended)
in series inside a single pole transformer tank shell for a
30 kV+ power supply for his big coil - and I still can't till
this day figure out how he crammed (2) 10 kVA transfor-
mer cores inside that one modest sized tank and still have
room to place the top bonnet lid with the HV bushings on
it. :^? The point is, you will run into some serious corona
and voltage standoff issues, not to mention primary capa-
citor robustness issues when you start trying to drive a
primary tank circuit with voltages of that magnitude. I'm
not saying that it's impossible, by any means, but it will
likely present itself considerably more of a challenge than
you were anticipating, though! And I think that you will find
the collective opinion of this group on that issue pretty
much reflects what I've said here.
Since you've obviously already purchased this 50 kV,
400 mA unit, my suggestion would be to go ahead and
plan on using it for somehting like a Jacob's ladder, once
you've given it a nice tank of oil to run in. It was most
likley originally in an oil-filled tank and was removed
for ease of storage, shipment, ect, but you will almost
certainly need to "repot" it if you intend to run it at its
nameplate voltage rating to prevent destructive flashover
of the high voltage windings. I use a nice sized x-ray
transformer to drive a wicked Jacob's ladder here:
http://www.youtube.com/watch?v=0dLTEOM3qQc
As for a Tesla coil power supply transformer, I would
take Bunnykiller's advice and just try to obtain a stan-
dard 10 kVA, 14,400 - 120/240 volt single phase pole
mount "pole pig" distribution transformer for this purpose.
As he stated, D. C. Cox (aka- Dr. Resonance) often has
some used 10 kVA, 14.4 kV pole pigs that he gets from
various utility companies that he sales for around $200 ea.
+ freight S&H. If you have a truck and live within say
300 miles of his location (Baraboo, WI area) it may be
worth your while to make a day trip of it and go and
pick it up yourself.
Safe coiling,
David Rieben
----- Original Message ----- From: <robert@xxxxxxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Tuesday, August 05, 2008 1:24 PM
Subject: Re: [TCML] Transformer
Thank you all for the advice. I did pick up that transformer for one
reason I was in the town where it was located working today, so I
saved on the shipping. I was also able to pick up a 15/60 NST also at
a sigh shop for free. The only problem is, it is a gfi type. Can the
gfi be removed? And can we work with that big xray tranny and make it
work also. I don't mind a good complex challenge. If you all can
stand holding my hand through it I' game to give it a go.
Thanks again for all the help so far.
Rob
KI4HXT
Sent via BlackBerry by AT&T
-----Original Message-----
From: Quarkster <quarkster@xxxxxxx>
Date: Tue, 5 Aug 2008 10:56:13
To: Tesla Coil Mailing List<tesla@xxxxxxxxxx>
Subject: Re: [TCML] Transformer
Robert -
You didn't provide any information on your intend use, so it is
difficult to make any sort of recommendations without more data.
If you intend to make a Tesla coil, an X-ray transformer is
inappropriate, especially for a first coil. The output voltage of a
50KV transformer is too high for Tesla coil use without the use of
exotic construction techniques, and finding or making a tank
capacitor that will operate at 50KV will be difficult and/or costly.
Conventional spark-gap Tesla coils typically utilize transformer
output voltages in the range of 7.5KV to 15KV. This allows the
transformer and tank circuit to operate with air insulation, rather
than requiring everything to be submerged in insulating oil. Tank
capacitors can be easily assembled from arrays of smaller, lower
voltage capacitors (MMC), ending up with an effective voltage rating
of 20-25KV.
Your best bet is to find an older (non-GFI) neon sign transformer,
10.5 to 15KV output at 30 or 60ma. These can frequently be obtained
at low cost from neon sign shops, or on eBay. Multiple transformers
of the same voltage rating can be connected in parallel for higher
current output.
The seller of the transformer in your link did not mention that
X-ray transformers are rated for an extremely low duty cycle
(typically <5%) to prevent overheating. If you want to run it for
10's of seconds, or longer, then you need to ballast it to reduce
input current, which will greatly reduce output current. The 50KV -
400ma "full output" rating is really only good for one or two
seconds, at most.
Regards,
Herr Zapp
Robert Davies <robert@xxxxxxxxxx> wrote:
Hello All, In my area here in Florida scrap metal prices are so high it
is basically impossible to find anything in the low budget or free
arena. It looks like I will have to buy a transformer. Which is ok by me
I just don't want to get stung. My question is what price range should I
be looking to pay for a suitable transformer. I found one on ebay
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=180271844951&ssPageName=ADME:X:AAQ:US:1123
Any advise would be most appreciated.
Thanks
Rob
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