Just wanted to put this out to the group, I am listing a number of Tesla
coil parts and here is the ebay link. I'm in the middle of prepping for a
move and I just do not have the time or the brainpower to work with these.
https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F123703141960
Help someone is interested because I bought them thinking I would work with
coils and I just don't have the time.
DJ
On Thu, Feb 28, 2019, 6:13 AM Don Anderson via Tesla <tesla@xxxxxxxxxx>
wrote:
> Here are some of my thoughts on EMI filters that I posted in reply to a
> question on Coilsmiths several weeks ago.
>
>
> EMI filters for Tesla Coil usage
>
> This may be a good EMI filter for your application,but look at the
> possible peak current problems. When measured in a 50-ohm system it will
> give you about 30 dBattenuation at 100 KHz, and your system likely will
> have an operating frequencyin this region, and thus the strongest emissions
> in this region. For voltageratios, 20 dB = factor of 10 attenuation, 30 dB
> = factor of 31, and 40 dB =100. Your system will not have 50-ohm input and
> output impedances, but this ishow filters are measured, and your real-life
> performance will be very roughly similarto these attenuations.
>
> There are 2 types of EMI signals to be concerned about.Common Mode
> (symmetrical) signals have the same signal on each power line asmeasured
> with respect to ground. Differential Mode (asymmetrical) have thesignals
> measured between the 2 power lines. Different parts of the filter areused
> to attenuate the two types of signals. With EMI suppression you are trying
> toattenuate the signals down to a level where they do not cause problems,
> youcannot totally eliminate them.
>
> Many EMI filters are designed to start attenuating above500 KHz, so find
> one that has adequate attenuation at your fundamentalfrequency of
> operation. At yourfundamental frequency of operation (probably around 100
> KHz), I like to have aminimum of 20 dB attenuation, and preferably 30 to 40
> dB. You can easily add severaluF of line to line capacitors (or several
> caps in parallel) to the filter toimprove low frequency Differential Mode
> attenuation (but this component willnot improve CM attenuation). The
> voltage rating should be 250 VAC or 600 VDCminimum, and it is best to use a
> “X” type safety rated cap which is designed tosafely operate on an AC line
> that has voltage transients. Keep the leads asshort as possible to minimize
> the lead inductance you add, as this will cause aresonance at higher
> frequency and the attenuation of the cap rapidly degradesabove that
> resonance.
>
> As frequency goes up, the attention of the filter usuallygoes up, at least
> until you get to the 10’s of MHz region where internal resonancesshow up
> and cause dips in attenuation. Your coil will generate and emit energyat
> higher frequencies, especially at harmonics of the operating frequency.
> Atoroid to ground discharge can excite powerful resonances in the MHz and
> 10’sof MHz region, and these higher frequencies will radiate easier and can
> causeinterference in other electronics.
>
> In a resistive load the peak current is 1.414 timesthe RMS current, and
> many filters are designed and rated for a resistive load. A rectifier
> feeding a large capacitor loadcan have the peak current (crest factor) 2 to
> 3 times the RMS current,occasionally higher. When you overcurrent an
> inductor it will saturate themagnetic core on which it is wound and the
> inductance almost disappears, andthe attenuation almost disappears. The
> inductor in this filter is a common modetype which has two windings with
> the line current thru one, and the returncurrent thru the other, so it
> should not saturate. But in the real world theseinductors are often made
> with unequal windings so they will also have somedifferential mode
> inductance, which means they can saturate.
>
> It would be safer to have a 30A filter for a 15 Arectifier/capacitor load.
> The defining parameter in my mind for a Tesla Coil EMI filter isthe low
> frequency or 100 KHz attenuation. Significant attenuation at 100 KHzmeans
> large (physical and inductance) inductors and large capacitors. These
> arelarge and heavy, so as a rule of thumb a filter that is light in weight
> doeslittle to attenuate the low frequencies, which are usually the
> strongest. Makesure that you have several inches of separation between the
> input and theoutput wires of your filter, as small amounts of capacitance
> between the wireswill cause very high frequency signals from the dirty side
> of the filter to leak into the cleanside.
>
> Almost all filters have line to ground caps which areneeded for common
> mode attenuation, and these also will inject several ma of 60Hz (50 in
> Europe) current into the ground connection, so make sure the power
> lineground wire is connected to the case of the EMI filter. Y type
> safetycapacitors are designed for line to ground operation, as a shorted Y
> cap willcause a dangerous situation with line voltage on your chassis.
> These are ratedat 250 VAC, but are usually made with caps rated at 3000 to
> 4000 volts toincrease the safety margin. Y caps are usually in the 2nF to
> 10nF range, aslarger caps will inject too much current into your ground
> system.
>
> As a good practice I like to add a 20mm (or larger)diameter MOV (Metal
> Oxide Varistor) to the power section as a line to linecomponent. Use a 150
> or 175 VAC part on a 120 VAC line, or a 250 or 275 VACpart on a 208 to 240
> VAC power line. Do NOT run these above their rated voltageor they will
> massively overheat. These act like a big Zener diode and will takea large
> transient (like a secondary arc to your power section) and clamp itdown to
> a medium transient.
>
> It is also a good design practice to add anappropriately rated (voltage,
> current, and interrupting current) white ceramictube fuse (not a clear
> glass tube), Littelfuse 314 (fast blow) or 326(slow-blo) or equivalent, to
> your power section just past your main on/offswitch. The ceramic tube fuses
> have a sand filling which gives them a much higher interrupting current
> rating. Fuses have a much faster opening time for a large overload or
> shortcircuit, and this means the breaker in your building branch circuit
> will notblow. This will help keep other people in the building happier if
> some thinggoes wrong in your coil, and will limit the fault current and
> thus the damageto your system.
>
> I hope that I have added some useful data to theconversation without
> adding too much confusion, but EMI is a very complexsubject. Do some
> reading on EMI when you have a chance. I am a retired EMC engineer so this
> is thereason for the data dump. It is nicehave a big parts box, and to now
> be able to design a circuit without having tobe cost effective in the
> design.
>
> Don Anderson
>
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