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Wow Terry, as inexpensive as the Velleman is, I would be scared of letting it ride on the toroid, especially on that raised up "pan" type platform yours seems to have there.
"High risk" for sure!!! But somebody had to do it
Zero damage and it really felt "comfortable"...
The voltage stress was actually very low "up there"...
Registered Member #75
Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711
Uzzors wrote ...
Followup question; how could you measure output power of an HV transformer without an HV meter. Say I could estimate the voltage by spark gap distance. What do I then measure the current between? The HV electrode and air? Simply pulling an arc will give the short circuit current, but voltage will be unknown. Or do I have to go via input power - estimated losses?
Output power allways depends on load impedance, but if you know the open circuit voltage and the short circuit current of you transformer, you can model it as a voltage source in series with the Impedance given by V_open / I_short. Matching this to an equal load impedance to maximize power gives you P_max=1/2 V_open * I_short.
For DC you can build a simple voltage meter by measuring the current through a loooong string of high value resistors, for high frequency AC you are probably better off guessing based on input power.
Registered Member #95
Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308
Thanks Joe. I just need to make sure my secondary is in proportion to the flyback transformer.
The power output is a lot more than I thought it would be. I'm using a standard flyback transformer, driven directly offline with a half-bridge. Open circuit voltage, measured by the striking distance with both spherical and needle electrodes, is ~17kV. (17.2 for needles, 16.7 for spheres.) Short circuit current is 80 mA. That gives an impedance of 212.5 kOhms and a whopping 680W with a matched load. Does that sound right for a single flyback?
What kind of impedance can I expect from a SGTC and what would the power be like when driving it?
Registered Member #75
Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711
It definitely does not sound right, but more in terms of being morally wrong than being a misscalculation! I have once connected a flyback to an off-line half-brigde and I got a MOT-like flaming arc for a fraction of a second before the breaker tripped. Also, if you go to a high enough frequency and drive the core deep into saturation, there is practically no limit for the instantaneous power you can get, the flyback will just overheat very quickly.
PS: I am not at all sure what happens to this impedance matching equation when you consider that a flyback has a lot of inductive and capacitive impedance in addition to the DC resistance, and that the 17kV you measured might be due to resonance. I am sure Steve would know all about this.
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measuring current of HVDC
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