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Re: Beating a Dead Horse - Neons

At 10:25 PM 11/3/96 -0700, you wrote:
>>From jgore-at-cyberramp-dot-netSun Nov  3 21:42:27 1996
>Date: Sat, 2 Nov 1996 01:15:02 +0000
>From: jgore-at-cyberramp-dot-net
>To: tesla-at-pupman-dot-com
>Subject: Beating a Dead Horse - Neons
>
>I think I'm more confused now than I ever was about protecting my 
>neon transformers. It's a big deal to me because I only have 5 left 
>and don't want to fry them. I've seen a certain person in Fort Worth 
>go through many of them (30 over the course of two years), sometimes 2-3 at
a time ;-)
>I'm sure I didn't understand all the Spice simulations, but I'm 
>more interested in what people have actually done anyways. I'd hate to 
>fry a neon based on theory, I simply can't afford the loss (i.e. no 
>money). So heres the deal: 
>If you have ever run a Tesla Coil with neons then please tell me 
>exactly what you used to protect it, with as much detail as 
>possible. Saying,"two chokes and one bypass cap", doesn't help much.


Well my filter setup has always been on the simple side. At first I used
only a safety gap. No chokes no bypass caps. This served me well until I
started up
the power curve. Once I got near the 1 KVA level the safety gap sound like a
rifle shot
going off. Clearly I needed to knock down the RF level coming back to the
transformer.
I got a couple of large ferrite toroids from Hosfelt Electronics. Wound 125
turns of
# 26 magnet wire on them. That should be close to 2.5 mh each. After putting
these chokes
in line my safety gap discharges now were soft pops.

I have only lost 1 neon transformer so far. And I lost it by placing a 500pf
doorknob
cap on each leg to ground. The transformer died in about 15 seconds. I
havn't used a 
bypass cap since.

So my setup consists of a close spaced safety gap and the two toroids. (1 in
each leg)
This has worked well at power levels up to 1.5 KVA.


>Here's my setup, which got two neons fried:
>
>I had a safety gap which fired intermitently to ground (a bolt 
>attached to each leg of the neon output with a center bolt to ground,  
>  ----   |  ----   ). After that came a 3 inch toroid choke on each 
>leg with about 10 inches of 18 gauge wire on each. (not enough I'm told).


Clearly your chokes are way to small. These probably only measure a few
microhenries. These might be worse than nothing. Small chokes can ring up 
and act like mini Tesla coils. You need millihenries of inductance. More the
better.
Wind a 100 or more turns of smaller wire on your toroids and I think you will be
better off. You dont need large guage wire here. Current is only milliamps. 




>For a safety cap I
>had 5 small doorknob caps which screwed together and were attached across the 
>neon outputs (series). 

Across the neon outputs? You mean from each output to RF ground don't you?
Sorry if I misinterpet.

Each one says,"2500 MMFD - 5KVAC" (I'm really not sure what
>MMFD means. I'm used to mfd and pf. Don't laugh, my major is psychology not
>electronics ;-)

mmfd stands for micro-microfarads. Thats the old designation for picofarads.
Depending on how many you used in series that seems like a lot of
capacitance for a bypass.
A couple of hundred pf would be plenty I would think.


>
>So there you have it. A recipe for burning up a neon! Anyone have a 
>better recipe?

I would say to leave off the bypass caps and rewind your chokes.  Also a little
series resistance would help dampen out any resonances you might be having. Of
course these will result in a little less output but so will a blown
transformer.

One other factor to consider is run time. A couple of minutes may seem a
sort time to
you but is an eternity to your poor neons. Keep run times short. I rarely
run more than
30 seconds at a time.


Hope this is of some help.
Mike Hammer

mhammer-at-midwest-dot-net