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Re: UK coilers ? + stuff (fwd)
---------- Forwarded message ----------
Date: Sat, 1 Aug 1998 17:04:53 EDT
From: Alfred A Skrocki <alfred.skrocki.sr-at-juno-dot-com>
To: tesla-at-pupman-dot-com
Subject: Re: UK coilers ? + stuff (fwd)
On Fri, 31 Jul 1998 18:37:50 +0100 Chris Swinson
<chris.swinson-at-zetnet.co.uk> wrote;
>Hi all,
>
>I've just joined the list to help and swap ideas with more experienced
>people.
Welcome to the list Chris! You certainly have the right idea of what the
list is all about.
>I haven't built a large coil, mine is only a 240 watter. I can get up
>to 9" sparks off my coil. Has anyone built a 240 watt coil and got
>bigger sparks than that ?
Yes, using a 230 watt OBIT (Oil Burner Ignition Transformer), 10KV -at- 23
ma., I got better than 36" sparks off the top torrid.
>My first question.... My secondarys resistance is about 77R, Does
>anyone know how much resistance I can actually get away with. I'm just
>builing a 200R coil just to see what happens.
You should try and get the secondary resistance as low as you possibly
can! Some have gone so far as to wind several layers of secondary
windings and connect them all in parallel
to get lower secondary resistance, and with good results, I might add!
>Has anyone tried a DC transistor driver, My high voltage input it a
>small 8Kv -at- 30ma, thats 240 watts.
There have been some experiments with DC transistor drive. You can find
messages in the archives on the subject. I might point out though that so
far results with tubes or transistors have not been as good as the spark
driven designs.
>If I used 160 volts at about 2A that would give about the same wattage.
But would this >work as well as the high voltage ?
No, generally speaking you want as high a primary voltage as you can to
yield a higher secondary output voltage, BUT ther is a limit of about
15KV above this voltage the coronal losses get too high and you get
deminishing returns.
>I know that the cap and spark gap would not be needed as the transistors
would have to >switch to about 600Khz anyway. As far as I can tell this
would work better and the coil >should run a lot smoother, Any thoughts
any one ? ?
You would still need good capacitors, it is fundamental to the operation
of a Tesla coil!
Many have conjectured that solid state drivers for a Tesla coil should be
better BUT in reality they suck! To get good output out of a Tesla coil
you need the "disruptive" discharge of a capacitor and so far this is
only accomplished with spark gaps.
>I also don't 100% understand when people say build coils with a 3:1
>ratio, can anyone enlighten me ? The ratio for my coil as I see it is
1:260
>so where do you all get 3:1 from ?
I don't know how your measuring you 1:260 ratio, turns perhaps? What we
mean by a 3:1 or a 4:1 ratio is the ratio of the length of a coils
windings divided by the diameter of the coil. For example a coil wound on
a a "7 inch" PVC pipe (actual diameter is 6.5 inches)
so you would have a 26 inch long winding to make a 4:1 ratio or 19.5
inches of winding for a 3:1 ratio.
>According to my secondary inductance calculations my coil is about 39
>mH, But actual measurement shows 7.4mH. Does anyone know is this
reduction
>in inductance is good ? As far as I see it , it is but as far as I can
>see it may increase capacitance which is bad.
Actually you want the secondary's inductance as high as you can get it
and you want the secondary distributed capacitance as small as possible
for maximum secondary output.
>Oh, I varnished my coil so that's why it's different.
Varnishing the coil may increase it's distributed capacitance but it
won't do have any
effect what so ever on the coils inductance!
>I was thinking of doing 2 coils the same, but lacquering one to compare
results, But can >anyone tell me what's what before I send the time doing
more coils ?
Never tried it but I would suspect that the coronal losses on the
un-lacquered coil
would cause it to perform poorer than the lacquered one.
>what's the output current of a coil ? I know the capacitor may well
>give a very small peek of up to 1000's of amps, But the current rating
of the
>wire in my secondary is about 140 ma, Does this mean I can only draw
>140ma or is there something else to it all.
Typically the current output of a coil like yours is in the micro-amp
range.
The current out put is in accordance with the conservation of energy
rule. ie the power input is the same as the power output (minus losses of
course) so since the voltage output is soo much higher than the voltage
input the output current must be accordingly much smaller.
>Has anyone tried a magnet as a discharge terminal. I used a old
>speaker magnet ( donut ) and I get evenly spaced sparks off it, about
every
>inch around the magnet. This is rather interesting to me, Anyone tried
>this or know why it does that ?
It is more likely that the spacing is due to the magnets geometry than to
it's magnetic field. That magnet is far to weak to have any noticeable
effect on the discharge of the coil!
>Has anyone got any thoughts on using a valve as a spark gap, I used a
>small ECC88 ( I think) there was 2 plate inside which were close
>enough for the spark to jump, note that I only used the valve not
heaters or
>anything else at all. My coil ran very well indeed. It was a lot
>smoother and the performance was a lot better. But it got a tad hot
>ans exploded so I decided that I ought to find out more about it if I
can.
Many people have tried different types of vacuum gaps with varying
results. I would suggest some kind of cooling arrangement for your
"valve' gap, or maybe several in parallel to share the load.
Alfred A. Skrocki
Alfred.Skrocki.Sr-at-JUNO-dot-com
Visit my Do-It-Yourself Aquarium WEB page at:
http://WWW.GeoCities-dot-com/CapeCanaveral/6251
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