Thanks Bert,
-Excellent, practical information.
<group>
I do plan to source a three Phase 5kV transformer or three separates since I
have the 3P generator operational and have wanted to build one of these for
several years now. Sources anyone?
Raytheon: I have not given up hope on splitting the windings at the center
point and making parallel star windings. V/2, 2I. I just can't do that stuff
just yet. There are four coils separated by neoprene on each leg. I will
verify that H1 come from the top one and the Wye tie point point from the
bottom. I hate to cut into any cotton wrap though.
In the center of the four coils is a wire that seems to join the top and
bottom two much like a center tap. If I measure roughly 1/2 DC resistance
from center to either side, I will have some hope and go further. I can not
think of a weird way this could be otherwise be wound, can you? Transformer
folks?
Jim Mora
BTW I do have such single phase Filter caps. Safely bleeding them in
reasonable time is another whole topic.
-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On Behalf
Of Bert Hickman
Sent: Monday, July 21, 2014 10:25 AM
To: Tesla Coil Mailing List
Subject: Re: [TCML] Paralell Diode considerstions. And the Deque Diode.
Resonace Charging
Jim Mora wrote:
> Hello Tesla Friends,
>
> Regardless of the outcome with my Raytheon Power Supply, I have completed
> the Six Pulse, Full Wave three phase rectifier strings. They are comprised
> of (54) each UF5408 1KV with a faster switch time than the more robust
> milspec 1N5408. The peak forward surge current is 150 amps at one cycle of
> 60Hz versus the 1N5408 300 amps. Both are speced 700 volts reverse RMS.
> Since there are effectively 6 Strings of (24) on three center tapped G10
> .125" x 1.5" x 24" for each polarity (over kill on voltage maybe), but it
is
> easy to shunt some if desired. The center taps are the H1, H2, H3
> connections. And the ends will be tied together for isolated Positive and
> Negative.
>
> I am working on the "Darwin Award" this year as the transformer tipped
over
> and broke my Fibula in the lower left leg - A great time to be making
diode
> strings!
Yikes - that had to smart! Hoping you have a speedy and full recovery.
>
> **** Here are the questions about the dequeing Diode design****
>
> (1) can the 2X resonant voltage come slushing back to it worse case and be
> seen on the cathode? Which if I had my way this would be about 22-25KV out
> (10KVA input power) say 5KV H1,2,3 transformer (12.2 KV calculated +,-)
> rectified for HV out of "some" 3P transformer.
In a classic line modulator (with a DC energy storage capacitor on the
supply-side of the charging reactor), the dequeing rectifier will see a
reverse voltage of no more than Vdc. This occurs when the tank cap is
fully-charged to approximately 2*Vdc.
BTW, if you do change to a single-phase HV power supply, you will need
to use a DC energy storage capacitor that's at least 10-20X the capacity
of your tank cap to supply energy between mains recharging pulses
without excessive sag.
>
> (2) what should be the max current rating be in such a scenario.
> (10KVA/12.2KV) min = .82 amps. These diodes like to idle at about 1 amp
1.5
> max at room temp to distruction. I would like to make this string 3amp
> capable by paralleling (2) strings. I have heard many discussions on this
> topic. Is it better to parallel each diode or entire strings? I would
think
> each diode... I know balancing is an issue that may need some form to
> address, but keep in mind I have a glut of 300 diodes on hand, remaining.
Assuming you still plan to use a 0.05 uF tank cap and wound your own 5H
charging choke with say 50 ohms of DC resistance, and ran at up to 600
BPS, then the peak, RMS, and average charging currents will be about
1.15 Amps, 0.75 Amps, and 0.68 Amps respectively and your output power
would be about 8300 watts (using lossy model). Since your rectifiers are
rated at 3 amps average current, you have plenty of headroom to increase
the power of your system while still using single rectifier strings. A
lower voltage distribution transformer or PT (1-phase) or bank of three
(3-phase) could be supported with your existing strings.
For example, suppose you increase to 0.1uF and reduced the reactor to
3H, the dequeing diode would see 2.03 A, 1.42 A, and 1.27 A for peak,
RMS, and ave currents, and would delivery about 14.1 kW of power at 600
BPS.
Paralleling diodes is not recommended. It's almost always more
cost-effective to use strings of higher-current diodes instead. If you
did want to parallel strings, entire strings should be paralleled, NOT
individual pairs of diodes. You'll still need to derate the total
current rating, OR add series balancing resistors to compensate for
forward voltage differences across strings. Immersing the strings in oil
will help to maintain strings at similar operating temperatures. See the
following applications note for more information:
http://application-notes.digchip.com/005/5-10703.pdf
>
> I'll post some pictures on my progress blog of the diode strings: nice,
> proven construction on road warrior Professional High Power "Boutique"
Tube
> Guitar amps which is what I have been doing for several years. Retired now
> except more fun stuff, sans broken bones or HV dire shocks ;-^) I promise
to
> use an over abundance of caution and respect going forward!
>
Please do - high power equipment can squash you like a bug (in addition
to cooking you in numerous other ways)! =:^O
> Jim Mora
>
> Next up: ... post reactor, I'll call transient reverse biased diode specs
to
> RF ground for the envisioned coil. I have a 4" RF air choke already.
>
> _______________________________________________
> Tesla mailing list
> Tesla@xxxxxxxxxx
> http://www.pupman.com/mailman/listinfo/tesla
>
>
>
Best wishes,
Bert
--
Bert Hickman
Stoneridge Engineering
http://www.capturedlightning.com
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