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Re: Safety Gap and some notes
From: terryf-at-verinet-dot-com[SMTP:terryf-at-verinet-dot-com]
Sent: Sunday, November 16, 1997 2:50 PM
To: Tesla List
Subject: Safety Gap and some notes
At 11:32 PM 11/15/97 -0600, you wrote:
>
>From: Vivian[SMTP:V.C.Watts-at-btinternet-dot-com]
>Reply To: Vivian
>Sent: Saturday, November 15, 1997 4:14 PM
>To: Tesla List
>Subject: Safety Gap
>
>Snip
>>The safety gap for your neon's should actually consist of two smaller
>>gaps - each going to a center RF ground, which is also tied to the case
>>of the transformer(s).
>>
>>Safe coilin' to you!
>>
>>-- Bert --
>>
>
>
>Thanks Bert for inf.. From what I can make from your ASCII diagram
>it looks as if you have the centre tap of the neon secondary grounded
>or is this just the neon case? My transformer has a secondary centre
>tap and associated earth lug (mains earth) which I have deliberately
>removed.
>
>Yes I have matched the capacitor to the neon for Max power transfer.
>I was also wondering that if I only run the coil for a minute or so
>at time if I could use a larger capacitor. The neon is a 10,000Kv 50ma.
>This give a source impedance of 200000 Ohms and at 50Hz a
>capacitor of 15nF. But the transformers DC resistance if only 5.6K.
>The inductance is greater than 20H (off the scale on meter).
>
>I could try and see what the regulation is by running it with a lower
>input voltage and loading the output. Is this at all feasible or
>am I trying my luck and should be thankful it works well now?
>
>Thanks again for help
>Viv Watts UK.
>
>
>
All,
When you connect a capacitor to the output of a neon transformer
it's characteristics change completly. Turn on transients, input and output
currents, etc. can easily go to destructive levels (gap switching seems
relatively easy compared to these (the capacitor protects the transformer).
The best setup is a variac and lots of meters, fuses, gaps, etc. Fuse the
input to the name plate rating (fast blow fuses) and gap the ouput to 1.7
times the rated AC output voltage and you are off to a good start. I would
not just plug one in to the mains without a varic or restence in the primary
because the sudden surge may be too quick to stop in time.
For reference I have found the following numbers to be accurate by
measurement, modeling and actual testing for a 120 volt 60Hz in, 15000 volt
60ma out neon. This should be somewhat close to Vivian's setup.
Primary Resistanc 0.25 ohm
Secondary Resistance 4745 ohm
Primary Inductance 0.475 H
Secondary Inductance 7422 H
Coupling K 0.955
As an example when I ran the transformer at 30 volts in and measured the
following:
Vin = 30 VAC
Iin = 0.2 Amp
Vout = 3955 VAC
Iout = 0
Now add a 17.25 nF cap across the output
Vin = 30 VAC
Iin = 4.6 Amps That's a lot of current for 30 volts in!!!
Vout = 5250 VAC 33% higher!
Iout = 33 mAmp Half the transformer's rating.
The real killer is turn on. Modeling suggest that spikes as high as 15
Kvolts peak can be generated on the output when the 30 volts is first
applied to the transformer with this cap across the output. I haven't
ventured into the 120 VAC input case yet but it looks like I should go slow!
I will be studying this more but so far it looks like neons live a very hard
life in our coils.
Terry