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Re: [TCML] Newbe's First Coil
If you want a cheap, sturdy capacitor--right now, no waiting--consider the humble saltwater cap:
http://myweb.cableone.net/grcarhunter/bottom.htm
http://myweb.cableone.net/grcarhunter/swc.htm
http://myweb.cableone.net/grcarhunter/bottle.htm
For 10kv@23ma, you need something in the range of 5-7nF. 12oz beer bottles work well, and they're good for about 0.8nF each. If you tack on another OBIT in parallel, just double up on the cap size.
Good Luck,
Greg
--- On Sat, 2/6/10, cbroring@xxxxxxx <cbroring@xxxxxxx> wrote:
> From: cbroring@xxxxxxx <cbroring@xxxxxxx>
> Subject: Re: [TCML] Newbe's First Coil
> To: tesla@xxxxxxxxxx
> Date: Saturday, February 6, 2010, 2:31 PM
> 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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