RF Choke discussion from The Tesla List &
Neon Sign Transformer Power Rating
updated: Sept. 26, 2009
Project in process
Original poster: "John H. Couture" <couturejh-at-mgte-dot-com> Ed - If you do the tests and make the graphs as I mention in my reply to Gerry I believe you will get the answers to all of your comments. Note in your calculations that as soon as the sec amps on the NST start the sec voltage reduces and the output wattage changes. The trick is to find the optimum conditions for maximum output power (watts). This requires a graph or other method because the power curve is a hump type. The tests will also show you that the VA out greater than VA in is not due to instrument error. John Couture
Original poster: Ed Phillips <evp-at-pacbell-dot-net> Tesla list wrote: > > Original poster: "John H. Couture" <couturejh-at-mgte-dot-com> > > Harvey - > > I don't believe this is a verification of the maximum power transfer > principle. The tests indicate that the maximum power available from a NST is > only about one quarter not one half of the nameplate rating. Note that one > half the voltage and one half the current gives one fourth the power. For > example the maximum output wattage for these tests was 59.3 and the > nameplate 225 watts or > > Max power = 59.3/225 = .2636 = 26.36 % > > It appears that very little power is available from NSTs for their size. No > wonder they produce such short spark lengths compared to distribution, > instrument transformers, MOT, etc. Spark length equations should take this > into account. I have not heard of any other coilers who have made these NST > tests. > > The other problem with NSTs is that the TC input impedance is generally > never equal to the optimum needed to get the maximum power out of the > transformer. To my knowledge no coiler ever tests to find the optimum > impedance for the NST he is using and then designing his TC input impedance > to match. This is not a problem with distribution, instrument transformers, > etc. > > The fact is that NSTs appear to produce much longer sparks compared to the > power available. Are we missing something regarding TC operation with NST's? > My tests show that it is possible to produce VA outputs greater than VA > inputs with combination resistance and capacitance TC loads. Does this > somehow provide an extra gain? > > John Couture A few points on which I'd welcome comments. Assume an NST rated at 15000 volts OC and 60 ma SC. The internal reactance will thus be (15000/0.06) = 250,000 ohms. If a 250,000 ohm resistor is connected to the terminals the total secondary circuit impedance will be sqrt(250000^2+250000^2), or 353,533.3906 ohms [good to may 2 decimal places but the little calculator turns out nice long numbers]. The total current flowing will be 15,000/353500 = 0.0424 amperes and the total power dissipated in the resistor will be 0.0424^2 x 250,000 = 450 watts and is indeed half the nameplate rating. Now change the situation a bit and put an 0.025 ufd capacitor (-106100 ohms reactance) in series with the resistor. The net circuit reactance is now (250000-106100) = 143899 ohms and the total impedance will be sqrt(250000^2+143899^2) = 288,456 ohms. The current flowing will be 15000/288456 = 0.052 amperes and the power in the resistive loat will be 0.052^2 x 250,000 =676 watts. Reducing the capacitance to 0.012 ufd (-221040 ohms) will result in a net reactance of about 29000 ohms and the total circuit impedance will be 251670 ohms; the current flowing will be 0.0596 amperes and the power in the resistor will be 880 watts. If the capacitance is reduced to the "matched" (resonant) value of 0.0106 ufd the circuit reactance will be zero and the voltage across the resistor will be 15000 and the power will be 900 watts. Think I got all those numbers OK but one can always make mistakes. Bottom line is that with a load with capacitive reactance you can indeed get an output power equal to the nameplate OC voltage and SC current. Since the leakage reactance is affected somewhat by the current flowing and is not necessarily exactly 250000 ohms these numbers are only approximate but they illustrate the principle. Note that, if everything were linear, the open circuit voltage of the transformer would approach infinity (insulation would fail and/or core would saturate first) and the short circuit current would be limited only by the internal resistance of the transformer. In TC operation the load is not resistive of course, but same very general principles apply. I'm sure some of the amazing results reported for systems using NST's are the result of near-resonant operation of the secondary. As for VA outputs greater than VA inputs I think such results have to be due to instrumentation errors. Ed
Original poster: "John H. Couture" <couturejh-at-mgte-dot-com> Ed - If you do the tests and make the graphs as I mention in my reply to Gerry I believe you will get the answers to all of your comments. Note in your calculations that as soon as the sec amps on the NST start the sec voltage reduces and the output wattage changes. The trick is to find the optimum conditions for maximum output power (watts). This requires a graph or other method because the power curve is a hump type. The tests will also show you that the VA out greater than VA in is not due to instrument error. John Couture ------------------------------------- -----Original Message----- From: Tesla list [mailto:tesla-at-pupman-dot-com] Sent: Saturday, October 04, 2003 8:33 PM To: tesla-at-pupman-dot-com Subject: Re: NST power rating con Original poster: Ed Phillips <evp-at-pacbell-dot-net> Tesla list wrote: > > Original poster: "John H. Couture" <couturejh-at-mgte-dot-com> > > Harvey - > > I don't believe this is a verification of the maximum power transfer > principle. The tests indicate that the maximum power available from a NST is > only about one quarter not one half of the nameplate rating. Note that one > half the voltage and one half the current gives one fourth the power. For > example the maximum output wattage for these tests was 59.3 and the > nameplate 225 watts or > > Max power = 59.3/225 = .2636 = 26.36 % > > It appears that very little power is available from NSTs for their size. No > wonder they produce such short spark lengths compared to distribution, > instrument transformers, MOT, etc. Spark length equations should take this > into account. I have not heard of any other coilers who have made these NST > tests. > > The other problem with NSTs is that the TC input impedance is generally > never equal to the optimum needed to get the maximum power out of the > transformer. To my knowledge no coiler ever tests to find the optimum > impedance for the NST he is using and then designing his TC input impedance > to match. This is not a problem with distribution, instrument transformers, > etc. > > The fact is that NSTs appear to produce much longer sparks compared to the > power available. Are we missing something regarding TC operation with NST's? > My tests show that it is possible to produce VA outputs greater than VA > inputs with combination resistance and capacitance TC loads. Does this > somehow provide an extra gain? > > John Couture A few points on which I'd welcome comments. Assume an NST rated at 15000 volts OC and 60 ma SC. The internal reactance will thus be (15000/0.06) = 250,000 ohms. If a 250,000 ohm resistor is connected to the terminals the total secondary circuit impedance will be sqrt(250000^2+250000^2), or 353,533.3906 ohms [good to may 2 decimal places but the little calculator turns out nice long numbers]. The total current flowing will be 15,000/353500 = 0.0424 amperes and the total power dissipated in the resistor will be 0.0424^2 x 250,000 = 450 watts and is indeed half the nameplate rating. Now change the situation a bit and put an 0.025 ufd capacitor (-106100 ohms reactance) in series with the resistor. The net circuit reactance is now (250000-106100) = 143899 ohms and the total impedance will be sqrt(250000^2+143899^2) = 288,456 ohms. The current flowing will be 15000/288456 = 0.052 amperes and the power in the resistive loat will be 0.052^2 x 250,000 =676 watts. Reducing the capacitance to 0.012 ufd (-221040 ohms) will result in a net reactance of about 29000 ohms and the total circuit impedance will be 251670 ohms; the current flowing will be 0.0596 amperes and the power in the resistor will be 880 watts. If the capacitance is reduced to the "matched" (resonant) value of 0.0106 ufd the circuit reactance will be zero and the voltage across the resistor will be 15000 and the power will be 900 watts. Think I got all those numbers OK but one can always make mistakes. Bottom line is that with a load with capacitive reactance you can indeed get an output power equal to the nameplate OC voltage and SC current. Since the leakage reactance is affected somewhat by the current flowing and is not necessarily exactly 250000 ohms these numbers are only approximate but they illustrate the principle. Note that, if everything were linear, the open circuit voltage of the transformer would approach infinity (insulation would fail and/or core would saturate first) and the short circuit current would be limited only by the internal resistance of the transformer. In TC operation the load is not resistive of course, but same very general principles apply. I'm sure some of the amazing results reported for systems using NST's are the result of near-resonant operation of the secondary. As for VA outputs greater than VA inputs I think such results have to be due to instrumentation errors. Ed