Re: NST protection - current

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi Rick,

There is a great excel file I have that includes this data at:

http://hot-streamer-dot-com/TeslaCoils/Misc/NSTtest.xls

This data was made for:

http://hot-streamer-dot-com/TeslaCoils/Misc/NSTStudy/NSTStudy.htm

but it has much other useful info in it too.  It needs to be cleaned up and
presented in HTML or some format all can read...  For your 15/30, a 7 or 8
amp fuse whould be fine.  It will draw more than 15 if the shunts saturate!

Cheers,

	Terry

At 01:28 PM 8/16/2001 -0600, you wrote:
>Hi Terry,
>
>Is there a simple rule of thumb to determine the value/type of fuses needed
>for NSTs?
>I'm running 15/30s but thought a general rule would be useful for all.
>
>
>Rick williams
>Salt Lake City
>
>----- Original Message -----
>From: Tesla list <tesla-at-pupman-dot-com>
>To: <tesla-at-pupman-dot-com>
>Sent: Thursday, August 16, 2001 12:55 PM
>Subject: Re: NST protection
>
>
>> Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>
>>
>> Hi Justin,
>>
>> There are three ways to kill and NST aside from it just randomly dying
>from
>> old age.
>>
>> 1.  The RF voltage gets back into the secondary winding.  The high
>> inductance of the winding tends to concentrate the voltage on the outer
>> layer of turns.  The RF may also tend to cut through the tar insulation
>> much more easily than 60Hz.  My filter uses resistors and capacitors to
>> remove much of the RF.  Also, placing the NST across the main gap instead
>> of the primary cap vastly reduces the RF going back to the NST.
>>
>> 2.  Resonant rise occures with the NST's impedance and the primary
>> capacitor ring at 60Hz.  If left unstopped, the voltage can jump to around
>> 80kV which will kill just about any NST.  Resonant size primary caps are
>> very prone to this failure and probably account for 90% of NSTs blowing.
>> LTR coils have primary caps large enough that this cannont happen.  I
>> usually recommend LTR caps now just for this reason.  My filter has saftey
>> gaps that will fire and stop an over voltage situation.  It also has solid
>> state MOVs which will also stop the over voltage if the saftey gap does
>not
>> (like it is miss adjusted).
>>
>> 3.  If an NST is used with a large primary cap.  There is an odd condition
>> where the current can become very high due to the magnetic shunts in the
>> NST saturating.  This vary's depending on the NST's contsruction.  A
>simple
>> fuse on the NST input will blow if this happens and protect the NST.
>>
>> If you use a good filter and input fuses, I don't think you can break a
>> good NST without a hammer ;-)  I tend to like "my" filter at:)
>>
>> http://hot-streamer-dot-com/TeslaCoils/Misc/NSTFilt.jpg
>> http://hot-streamer-dot-com/TeslaCoils/Misc/Filter.jpg
>> http://hot-streamer-dot-com/TeslaCoils/MyCoils/BigCoil/protection.jpg
>> http://hot-streamer-dot-com/TeslaCoils/MyCoils/SmallCoil/small_protection.jpg
>> http://hot-streamer-dot-com/TeslaCoils/MyCoils/MyCoils.htm
>> http://hot-streamer-dot-com/TeslaCoils/MyPapers/MyPapers.htm
>>
>> Cheers,
>>
>> Terry
>>
>>
>> At 02:18 AM 8/16/2001 -0400, you wrote:
>> >Well, I burned out another one of my 15kV 60mA NST's today. That's the
>second
>> >one, and I've only got one left. After the cursing stopped, I got to
>> >thinking. After I while, I came across an idea for protecting NST's. I
>don't
>> >know if it will work, but I'll ask you guys and see what you think. A
>couple
>> >of days ago, I was asking about using microwave oven caps as a tesla tank
>> >capacitor. Everyone that responded told me that they won't work because
>they
>> >are lossy at RF frequencies. They are intended for use at about 60 Hz. So
>> >here's the idea: Why not place lossy type capacitors between the tesla
>tank
>> >circuit and the NST. I'm not an electronics expert, so someone would have
>to
>> >come up with a proper setup. The 60Hz coming off the NST would pass
>through
>> >the caps without any problem, but any RFI coming back through the circuit
>> >would be turned into heat before it could damage the NST. Of course some
>> >other type of capacitor could be used beside microwave oven caps, which
>would
>> >be quite bulky. I have no idea if this will work, but I thought I might
>as
>> >well throw it out there. I'd like to know what some of you guys out there
>> >think.
>> >                                Justin
>> >
>>
>>
>