Hi Stephen,
Stephen Hiscock wrote:
Bart and fin wrote:
"I get around 600 something turns....... "
"Yes, 648 turns at 32 tpi. I would expect Ipeak to range 185A to
1130A (15/30 up to 15/180). The primary details are important as
geometry greatly influences Lpri and thus Ipeak. Top loads play a
role also since primary resonance is based on an accurate f2 with all
components in place. So if the system is listed in some detail, then
Ipeak is better guesstimated."
The figures I gave you are wrong, but How were the figures above
calculated?
I assume your asking about the currents given.
Ip = Vp x sqrt(Cp/Lp), where Vp = 15kV x sqrt(2) = 21.2kV. C and L are
from the cap and primary figures.
Say we look at five 15/30's with 32nF. The primary should tune in at
about 5.9 turns with an L of 22.3uH.
Ip = Vp x sqrt(Cp/Lp) = 21200 x sqrt(32nF/22.3uH) = 803A.
I meant to say that the Primary is 30 to 100 micro Henries (not
microFarads) sorry silly mistake.
and the Secondary is 30.25 inches winding length at 32 turns/inch (
again sorry) so 968 turns total
the former is 6.5inches diamater
The top toroid is 6 inch diameter ring and 6 inch diameter inner ring
and 18 inch total outside diameter
eg: (circles represent the toroid) = in courier font it should look ok
OOO OOO
OOOOO---------OOOOO
OOO OOO |<-6->|<--6-->|<-6->|
|<----18 inches---->|
The secondary should be roughly 185kHz assuming 22 awg at 968 turns
with the following toroid.
yeah the Primary circuit would have two of my transformers as a
minimum (and 6 at a maximum)
I fired it up the other night I used 2 transformers rated at 15kV and
30mA each
so 15,000 volts at 60mA.
12nF is my primary capacitance (but as a maximum I could have 36nF)
The primary was tapped at the 10th turn out from the middle. (and as
a maximum could be the 4th turn - but its not working properly)
The primary is 12.5 turns total Turns
The dimensions are 13.5 inches inside diameter and 37 inches outside
diameter.
with 1 inch between turns.
as it is at the moment I'm only getting 6 inch sparks at the best
tuning!
Yipes! That's a problem to deal with, but not related to the question
(think "gap" for that problem).
I'm seeing a tune point of 9.6 turns with the 12nF, so your 10 turn
tune point as listed above is close enough that I know I'm near.
So in this situation:
Ip = Vp x sqrt(Cp/Lp) = 21200 x sqrt(12nF/60.85uH) = 298A.
And with this you can see how L and C dictate Ipeak as compared to the
5 NST case earlier. If a six NST case, then near 1000A.
(but sometimes I would hook up extra capacitance and transformers)
each transformer I have is 15,000 @ 30mA so my capacitance for each
transformer should be 6nF right?
Not necessarily. 6nF is almost resonant with a 15/30 NST. We try to
stay away from transformer resonance as the voltage is allowed to rise
above and beyond what the NST secondary winding insulation can handle
(NST's can die if the static gap is opened up wide enough). So we try
to go a little larger than resonance if possible. Roughly, 1.5 x Cres
value (but it does vary from coiler to coiler at about 1.3 to 1.5 x
Cres on average).
You should adjust the gap without the cap across the NST first (just
the gap and NST on a workbench). Open the gap until the NST cannot
fire. Then close up the gap until the gap just fires consistently.
Leave it there from then on. This simple procedure ensures your gap
voltage is clamped at it's maximum cold value (and saves NST's from a
needless death).
The tuning point for the biggest capacitance I can't verify because I
think my capacitor died.
But it should scale up right when I repair the capacitor bank?
just like the primary transformers? eg if I use 2 x the capacitance
then the peak current should be twice as large?
Yes, if you go from 12nF to 24nF "and also" adjust Lpri accordingly
for resonance, then yes, the current will be 2X. But if you simply add
the C without tuning Lpri, then it will be less.
Is that enough info for a ball park Ipeak figure so I can work what
IGBT's I need for a SISG?
It's fine for now. However when listing the primary in the future,
give tube size and if the spacing is edge to edge or center of wire to
center of wire if you happen to list that spec (actually with ID and
OD, tube size is really all that's needed). The ID's and OD's were the
most important and you gave those. The info we had was enough to guess
on the tube size and spacing reference.
Regards,
Bart
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