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Hi Phil and all,
Phil wrote:
(I've jumped around a bit too different emails here, hope you can follow)
Bert's figures in this vary from what Richie's figures give. Now I know that
assumes the calculator faithfully reproduces Richie's formulas, but I'm
certain after a lot of testing it does, so who's right, Richie or Burt?
I realise the smoothing cap will vary with 3 phase AC admittedly, but after
it's rectified it's all DC regardless, so the inductor and tank cap I would
consider to be the same as for our single phase AC input.
The biggest difference between Richie's model and the spreadsheet
calculator is that I use a lossy charging circuit model that takes into
account charging inductor losses. With inductor losses, the peak voltage
reached by the tank cap is always less than the lossless case (2 x Vdc).
The lossy model I use came from Sarjeant and Dollinger's book, "High
Power Electronics". If I set charging inductor losses to zero, I get the
same answers as Richie's lossless equations.
Also, for a rectified FWB single-phase power source with a DC storage
cap, I calculate the effective loop capacitance (the DC storage and tank
cap in series) in order to determine the effective resonant frequency of
the charging circuit. If the gap fires between mains peaks, the DC bus
voltage sags, reducing the peak tank cap voltage. The higher the break
rate or lower the DC cap value versus tank cap, the greater the voltage
sag. Using a cap that's 10-20X the tank cap size reduces, but does not
eliminate bus voltage sag. If I use a very large storage capacitor and
no inductor losses, I get the same answers as Richie's site.
Finally, for 3-phase operation, I assume a 6-pulse (good) or 12-pulse
(better) rectifier driven from a low-impedance transformer. In the
6-pulse setup (Jim's case), I left in the 10x DC storage cap in the
model to reduce HV bus ripple and sag for break rates in the 400-600 BPS
range. However, as Greg mentioned, it may not be necessary if one is
willing to accept mains ripple on the DC bus, and it is definitely not
needed in a 12-pulse system.
Richie's page is without a doubt the best reference on resonant charging
for TC hobbyists on the net. However, since the DC resonant charging
model and equations assume an ideal DC bus and lossless charging
inductor, the predicted tank voltage and output power will be somewhat
higher than what is observed within an operating DC coil.
Best wishes,
Bert
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The winding method Bert describes is fine if each layer has a large voltage
differential. One end of each layer only ever having double the layer
voltage differential, instead of four times the level, but as Bert says with
the 'pie' shape arrangement Stefan has used, the layer differential is going
to be pretty low anyway. It really all depends on room available; as you
would need two layers of inter layer insulation to do it that way. (This
probably won't come out right on the witchcraft machine you use.)
8kv 1 1 1 1 1 1 1 1 1 1 10kv
........................<- insulation paper (dots)
|______________
|
........................<- insulation paper
6kv 1 1 1 1 1 1 1 1 1 1 8kv
........................
|__________________
|
........................
4kv 1 1 1 1 1 1 1 1 1 1 6kv
........................
|_________________
|
2kv 1 1 1 1 1 1 1 1 1 1 4k
...................
|________________
|
....................
0kv 1 1 1 1 1 1 1 1 1 1 2kv
If room allowed I will wind that way as after running through it my head I
#now# realise it may actually be a bit easier to do. (hard to explain in an
email)
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Yes I prefer 300 bps as a max as well.
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Stefan has built large coils see
https://www.youtube.com/watch?v=Abr3rxYUH5o&list=UUm1yOqvHPOtyktC9lpS3Ffw
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If you want to see the sicko side of gun worship, look at some of the Yank
gun videos!!
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Found this site near me: http://www.transformers.uk.com/
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Phil.