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Bypass Caps + Wire Gauge
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To: tesla-at-grendel.objinc-dot-com
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Subject: Bypass Caps + Wire Gauge
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From: richard.quick-at-slug-dot-org (Richard Quick)
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Date: Sun, 26 Nov 1995 20:29:00 GMT
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Quoting gcerny-at-ix-dot-netcom-dot-com (Glenn Cerny):
> Richard,
> Your follow up to my earlier post has me wondering how to
> connect my bypass caps into my system. I have the 40000mmfd
> -at-30kv from HVPress. I was thinking that I would use one on
> each leg to rf ground somthing like below:
I added in my own ACSII artwork to show more detail:
X1
---- -------------------------------------nnnnnnnnnn--TANK-CIRCUIT->
) ( | | RF1
) ( ------- BC1 |
) ( ------- |
) ( | *
) (--GRND------|-----GRND----* SG
) ( | *
) ( ------- |
) ( ------- BC2 |
) ( | | RF2
---- -------------------------------------uuuuuuuuuu--TANK-CIRCUIT->
Where:
X1 = Is the step up transformer with grounded center tap
GRND = Dedicated RF Ground for the HV wiring and secondary coil
BC1 = Bypass Capacitance
BC2 = Bypass Capacitance
SG = Safety Gap w/grounded center post
RF1 = Radio Frequency Choke
RF2 = Radio Frequency Choke
This circuit should be set up such that the values of BC1 & BC2 are
matched or at least close in value. The same would also go for the
values of the inductance RF1 & RF2.
> Using one cap per side with a common rf ground in centerpoint
> to each leg. I think you get the picture. Can you recommend
> if this is good, or perhaps a better design available. I did
> buy 4 of the caps. If more are needed, I'll get them.
The diagram above shows how I wire the HV filter/safety gap into
the HV buss that supplies the Tesla tank circuit. This is assuming
that I am using a grounded center tap power supply like a neon or other
center tap ground transformers. You will need more than one .004 MFD
capacitor in series between each HV buss and the ground. You have
four of these already, I would purchase at least two more, preferably
four more.
I have used these exact same caps in several filter boards. I have
found that you need at least three of these caps in series between
each HV buss and ground when using 9kv or 12kv neons, and four
of these caps in series between the HV buss and ground when using 15
kv neons. Check the caps and ground conductor for warming as an
indication that too much bypass capacitance is in the circuit. Too
much bypass capacitance allows parasitic oscillations between the
power supply and the ground, a condition which must be avoided to
prevent fires and power supply failures. Generally I don't like
using much more than .001 MFD of bypass capacitance between any
HV buss and ground, or directly across the HV buss. This is one
instance where a little less capacitance is really better than a
little more.
Word on the Net has it that Nick Andree, 305 Wisconsin Ave.,
Oceanside, CA 92054 has these same capacitors priced under $5.00
each. It does not hurt to have a dozen or so of these on hand.
> Topic 2: What gauge wire should I use for my primary hook-up?
> Between my cap and the TC primary I was thinking of 8ga THHN.
> After computing the possible current peaks, I don't know if this
> is sufficent. What do you think? I have 100' of .250 copper wound
> in a very shallow dish with a id of 9.5 and an od of 29". My cap
> is one of the commercial ones. The driver is 6kva -at-12,000v. The
> initial coil is 700+ turns of 22ga on a 4" acrylic form with several
> torrids to choose from the smallest being 3X26.
Sounds like a very nice set up. I have found that fine stranded DC
power transmission wire is satisfatory for wiring up the tank circuit
proper. Use a conductor with a diameter at least as large as your
primary conductor. Given the power levels you are going to be jumping
into soon you could have gone to a 3/8 or even 1/2 inch diameter con-
ductor for your primary winding. At this point it is a minor issue.
Some good tank circuit conductors include: soft copper tubing of the
same type used for the primary coil, doubled or even trippled thick-
nesses of flat aluminum or copper strap, and DC power transmission
cable (battery or welding type).
> If you have a favorite circuit design showing placement of various
> components, please send that along too. I am really undecided how
> to approach the design for cap, gap, choke, safety gap placement.
> I have seen a lot of designs to choose from and the "classic" is what
> I am leaning to.
TESLA COIL SCHEMATIC ---------
| | T1
---------
O
X1 C1 O
RF1 | | O L2
O---------nnnnn---------------| |----- O
||O | | | | | L1 O
||O | | | O O
-----O||O * SG * |--->O O
O||O----*---|Gnd G1 O O
-----O||O * * O O
120 ||O | | O O
Volts ||O | | O O
O---------uuuuu---------------------------O O
RF2 |
|
Gnd
X1 = Neon Sign Transformer, grounded center tap
SG = Safety Gap.
RF1 = Radio Frequency Choke
RF2 = Radio Frequency Choke
G1 = Main system (tank circuit) Spark Gap.
C1 = Tank circuit capacitor
L1 = Primary Coil.
L2 = Secondary Coil.
T1 = Toroid discharge terminal
Gnd = RF Ground.
I have deliberately left out bypass capacitors to show this circuit
in a simpler form. The detail of the bypass filter schematic for
center tapped power supplies was diagrammed previously.
Now for those of you who are using power supplies that do not
have a center tap ground (two bushing pole pigs for instance)
the correct bypass/filter schematic appears below:
X1 RF1
---- -------------------------------------nnnnnnnnnn--TANK-CIRCUIT->
) ( | |
) ( | |
) ( | BC |
) ( ------- * SG
) ( ------- * ---|grnd
) ( | *
) ( | |
) ( | |
) ( | |
---- -------------------------------------uuuuuuuuuu--TANK-CIRCUIT->
RF2
Where:
X1 = is the step up transformer with grounded center tap
GRND = Dedicated RF Ground for the HV wiring and secondary coil
BC = Bypass Capacitance
SG = Safety Gap w/grounded center post
RF1 = Radio Frequency Choke
RF2 = Radio Frequency Choke
When using a transformer without a grounded center tap it is best
to place the bypass caps across the line without a ground reference.
I put four of the Sprague .004 MFD 30kvdc barium titanate (ceramic)
in series and place them directly across the HV buss for the bypass
capacitance. This method has worked extremely well for me in con-
juction with a moderate RF choke inductance. I always place a
grounded center post between the two hot electrodes of the safety
gap to provide a ground reference for the power supply/tank
circuit in the event of a flashover.
The coil schematic could look something like this:
TESLA COIL SCHEMATIC ---------
| | T1
---------
O
X1 C1 O
RF1 | | O L2
O---------------nnnnn---------| |----- O
||O | | | | | | L1 O
||O | | | | O O
-----O||O |BC *SC * |--->O O
Line> O||O ----- *--|grnd G1 O O
-----O||O ----- * * O O
||O | | | O O
||O | | | O O
O---------------uuuuu---------------------O O
RF2 |
|
Gnd
Richard Quick
... If all else fails... Throw another megavolt across it!
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