Re: [TCML] Newbe's First Coil

[cbroring@xxxxxxx]

I want to thank everybody who commented on my new Tesla coil.  Your 
input was very helpful.  I thought I may give an update.
Since the initial test I rebuilt the top load buy  wrapping the cookie 
tin with 4 inch diameter aluminum duct forming a 18 inch wide toroid.  
I then taped on a small nail to encourage the sparks to start.  This 
really didn't much change the length of the streamers but they were 
noticeably brighter.
I added a dedicated 8 foot ground rod for the RF side of the circuit.  
No real change in performance.
Then I built a 4 segment spark gap out of copper pipe fittings.  This 
worked noticeably better but got hot and the gap spacing closed up.  So 
I rebuilt it and added a muffin fan.  This worked a lot better, had a 
real snappy sound and significantly longer streamer from the top 
load... for about 10 seconds.  Then the fun stopped! I guess the new 
spark gap overstressed the ceramic capacitors and one of them quietly 
broke down.
So now I'm in the market for a new capacitor.  From what I read a MMC 
is the way to go, but I'm kind cheap and it would probability cost as 
much as I have in the whole coil so far.  Also, even after lots of 
reading up,  I'm a bit confused about choosing an appropriate value 
both in capacity and breakdown voltage.  Do I need more then one string 
in parallel to handle the current?  I purchased another OBIT on Ebay so 
I will have 2 parallel identical 10kv 23mA transformers powering it.
I haven't completely ruled out making my own capacitor.  The party cup 
design looks intriguing.
Is there a down side to going big with the capacitor value with the 
thought in mind that I may drive the coil with a some somewhat bigger 
power supply in the near future.  I have a number of 6-7 kv  radio 
transmitter plate transformers around here that I may wish to try, so 
if  I'm buying expensive new parts, I may want to give myself some room 
to grow.  My thought is that if the capacitor value is a bit larger 
then optimum I may have trouble charging it fully with the limited OBIT 
power supply, but is this a big liability in performance?
Again, any suggestions are very much appreciated.

Charlie
K3YA




-----Original Message-----
From: cbroring@xxxxxxx
To: tesla@xxxxxxxxxx
Sent: Sun, Jan 31, 2010 1:21 pm
Subject: [TCML] Newbe's First Coil


Hello to the members of this list.   For no particular reason I built a 
Tesla Coil this winter.  Just got it running, more or less.  So 
(hopefully) here are a couple of photo's of what I put together. 
 
http://img651.imageshack.us/img651/5567/1000420.jpg ;
http://img683.imageshack.us/img683/5931/1000424e.jpg ;
http://img651.imageshack.us/img651/5043/1000425.jpg ;
http://img651.imageshack.us/img651/5164/1000427.jpg ;
 
The transformer is a 10kv 23mA oil burner trans.  Primary is about 12 
turns # 14 sold house wire 10" diameter with a couple extra taps 
available.  Secondary is 1300 turns #27 on 3.5 inch pvc.  Spark gap is 
2 nails spaced about 5/16"  Capacitor is   two 6000pF 30kv hokey puck 
ceramics, and one shows a slight temperature rise with use.  Top load 
is a cookie tin and bent pizza pan.  The ground is the house wiring 
tied in to an extensive ham radio/ lightening ground system. 
 
It really doesn't work that great.  I removed a coupe turns and moved 
the tap around to get the best coupling I could.  I get a ring of 2 
inch sparks of the pizza plate.  I put a screwdriver on top and get 3-4 
inch sparks off that.  I haven't tried bringing a grounded probe to the 
top load yet.  Anyway, I read that the ceramic capacitors are not 
really durable and one of mine shows some heating after a minuet or so 
of on time to. I think I need to work on that next.  I expected a 
little more out of it even with the 250 watt power transformer. 
 
I need to figure out how to ground the thing.  I need a better 
capacitor. I have lots of big transformers and DC power supplies to 
play with once I get the coil working a bit better. 
 
Any suggestions are much appreciated. 
 
Charlie 
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