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Re: NSTs and Cap Charging.
In a message dated 99-04-10 05:29:58 EDT, you write:
<< Original Poster: "Malcolm Watts" <MALCOLM-at-directorate.wnp.ac.nz>
> Further to the discussion on resonant charging, I decided to run
> some figures through the mill to see whether one really could do
> better than the VA faceplate rating. NB - this is not modelling,
> just looking at the calculations. For this purpose, I've assumed that
> the experimentally determined value of cap that appears to give best
> results is 2x the resonant value and gets charged to SQRT2*Vrms. I've
> further ignored the consequences of opening the gap up to 2.22*Vrms
> for the resonant case.
> A typical transformer: 12kVrms, 60mArms, Fmains = 50Hz, BPS = 100.
> VA rating = 720
> Case 1: resonant charging
> Based on V/I = Zcap, Cp = 15.92nF
> If gap is set to 26.64kV (assume no losses), then Ec = 5.65J roughly
> so power = 565W, less than the VA rating.
> Of course one wouldn't normally open up the gap to this extent so one
> might assume that you get firing at 2Fmains at Ec = 2.3J which means
> a throughput of 460W or so.
Malcolm, all,
It is possible that using a static gap, the NST has a harder time
drawing excess power, vs. sync rotary. Using a sync rotary, you could
probably use the 565 Watt figure. Since the losses are so high in
the NST, it would need to draw maybe 920 watts to output 565 watts,
I would think. Also, many coilers (such as myself), often crank up
the input to 140 volts or so which will increase both the input and
output power of the NST.
My recent tests showed 740 watts input to the 360 watt rated NST
using resonant charging, at 120 volts input. I think the power getting
to the caps is considerably less than 740 watts due to NST losses.
I'm using the lab type wattmeter to measure input to the NST. I
observed the input current waveform and it's not too distorted (not
much harmonic energy), so the wattmeter should be reasonably
accurate.
> Case 2: larger capacitor
> Let Cp = 32nF and assume it charges to 17kV in a half cycle.
> Then Ec= 4.62J and throughput = 462W.
> In neither case is the VA rating of the transformer exceeded.
> Comments? Flaws?
With the larger cap, with static gap or sync rotary, I saw below rated
power being drawn by the NST, unless I turned up the input voltage
to over 120 volts input. But I have to try fiddling a little more with
the sync phase to see if I can get it to draw more power at 120 volts
input.
BTW, if any of my postings of yesterday seem to conflict, it is because
some where written before my tests, some after.
John Freau
> Malcolm
>>