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Registered Member #2998
Joined: Tue Jul 13 2010, 08:34PM
Location: Swedish forests.
Posts: 26
I'm not surprised. The current through that thing might be half an amp at those voltages. And that's one dangerous HV source! From what distance does the arc start? Not drawing, but starting?
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
the air gap can be inside leg only or it can be in both legs, but ive never seen one only on the outside. remember the airgap is high reluctance, so thats where (in the gap) the magnetism exists, the core has very little magnetic energy in it, even at the same flux density.
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
Patrick wrote ...
the air gap can be inside leg only or it can be in both legs, but ive never seen one only on the outside. remember the airgap is high reluctance, so thats where (in the gap) the magnetism exists, the core has very little magnetic energy in it, even at the same flux density.
i think i explained that right.
I stand with those who say that air gap can do its job anywhere in the magnetic circuit. But as the TI white paper says, gap within the coil generates less stray magnetic field. If you see a gap on the outside, there's probably another on the inside; such a double gap can be adjusted by the designer without getting a different part number.
Adding an airgap greatly reduces the inductance of any coil on the core, but greatly increases the magnetic energy storage of said coil (by allowing much more magnetizing current without saturation). It's reasonable to consider that the energy storage is almost entirely in the air gap, not in the highly permeable core material. Flux B is continuous around the whole loop; magnetomotive force H is almost entirely dropped in the gap. Here's a numerical example:
When the goal is to approximate an ideal transformer (see the hv wiki), not a flyback converter, then you skip the airgap. No energy storage is required, and we minimize the magnetizing current by maximizing the primary inductance.
Registered Member #3114
Joined: Sat Aug 14 2010, 08:33AM
Location:
Posts: 608
i had a 315mA fuse, so i connected it the the out puts on my homemade flyback and the fuse blew up! The only other fuses i have a 5,2 amp. how many amps dos it take to kill you?
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
probability of current lethality, is highly variable especially at high freq and high voltage, and enviromentally dependant, so there is no "magic" number, the higher the current the greater the probability of death. also, fuses are not a good way to measure current, the voltage drop of 2kV @ 2mA may blow a 315 mA fuse.
also, time and impulse arrival may matter too, for instance the T-wave part of the human heart signal is the most vulnerable, very little current arriving or leaving durring the half round t-wave phase is possible to stop heart function at any current, but timing of stopping the heart is not easy even with todays modern medicine, so just dont assume electricity is non-lethal, even tasers can cause death in the uA range.
assume any current above 40 or so volts is possibly lethal. always ware PPE. you dont have to be shocked to be killed either, a near encounter with arc, flash or explosion can blind, cripple or kill too, your body doesnt need to be part of the circuit to die. remember, liquid copper can be harmful/fatal too. these are the things i have been taught or learned, i have had close calls.
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winding a secondary on a flyback core
