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Registered Member #503
Joined: Sun Nov 19 2006, 06:37PM
Location:
Posts: 59
Hello folks,
I was going through this thread : Dr.KiloVolt says that the winding should be on opposite legs of the core to avoid problems due to pri-sec inductance when drawing sparks. Are there any advantages to this configuration? When I was making a 5kV DC supply I had ordered samples from a couple of makers and managed to get results from the one shown wound in the picture.Any ideas on what I could use the other one for ? It looks too cute to be used as a paper weight :) ]pics.pdf[/file]
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Well, if you want to draw sparks, you need some kind of a impedance in the circuit to limit the current.
The usual way of accomplishing this is with an inductive reactance.
Now, you have the choice to either use an external inductor, or to "integrate" the inductance into the transformer. The latter can be realised with a clever configuration of the windings on the core.
With the coils close together and on the same axis, the coupling will be high, so the reactance (or leakage inductance) of the transformer is low and not much limiting takes place. The result is that very high currents will flow in the case of short circuit, and something will most likely be damaged (inverter or the transformer).
However, you can decrease the coupling dramatically by putting the primary in a different place on the core than the secondary, while the coupling is minimum (the leakage is maximum) when the primary is opposite the secondary on the core and this is the point when maximum current limiting takes place.
If the limiting is sufficient or not, depends on many factors but mainly the transformer construction. Additional inductance may be required to get the current down to the wanted level, or on the other hand too much limiting can take place, which can be usually "fixed" by putting the primary closer to the secondary on the core.
The coupling can also be controlled by how much area the primary takes on the core, while less area/stacked winding results in more current limiting than with a single layer taking large space on the core.
Registered Member #503
Joined: Sun Nov 19 2006, 06:37PM
Location:
Posts: 59
Hello Dr.KV
Thanks for the quite useful reply. Actually , I wanted to know if there are any advantages of high coupling factors (pri. and sec. windings co-axial). Lesser primary turns or current perhaps ?
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
The advantages and disadvantages all arise from that the coupling is higher.
Advantages would be for applications where you want a good output regulation, ie. the voltage does not drop much under load.
If you want to draw arcs, then the disatvantage is that you'll absolutely need an external inductor to limit the current. Also with the windings co-axial, the heat dissipations add together so the windings run somewhat hotter.
The primary turns and current are the same in both cases. Actually everything is the same except the coupling / leakage inductance.
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