# Re: Three phase rectifiers

```Original poster: "Bert Hickman by way of Terry Fritz <twftesla-at-uswest-dot-net>" <bert.hickman-at-aquila-dot-net>

Tesla list wrote:
>
> Original poster: "Greg Leyh by way of Terry Fritz <twftesla-at-uswest-dot-net>"
<lod-at-pacbell-dot-net>
>
> Original poster: "Finn Hammer by way of Terry Fritz
> <twftesla-at-uswest-dot-net>"
>
> > 3-phase is cool, but also obligating, since noone should ever draw more
> > than, say, 35 amps from one phase only, since this will skew the grid.
> >
> > I think the 3-phase rectified supply would be more used, if the function
> > of the charging choke was better understood.
> >
> > Would you please explain how to determine a proper sized charging choke
> > in a system, where transformer voltage and capacitor size is already
> > given, so that it results in the desired doubling of the voltage across
> > the cap/vs the input voltage, while keeping the current from the
> > transformer to the gap during ringdown low enough  to allow quenching of
> > the gap without making a rapid recharge of the cap impossible.
>
> Basically, you start with determining the max break rate desired.  An
> example:
>
> Max desired break rate = 400 BPS
> Cpri = 0.3uF
>
> The resonant charger frequency should be 200Hz, since the capacitor
> will charge in 1/2 cycle of the resonant charger frequency.  You would
> then select a value for the charging reactor that will resonate with
> the Cpri at 200Hz.
>
> Lchg = 2.11H
>
> Note that this value is completely independent of Vpri, line frequency,
> or any variables other than the maxBPS and Cpri.  The charging action
> of the reactor has no effect on gap quenching, since the reactor current
> is zero when the gap fires, and is held at zero by its massive inertia.
> --
>
> -GL
> www.lod-dot-org

Finn and all,

Some further comments. Assuming you use the following circuit (view in
fixed font):

Lc     |\ |            || Cp
------o---0000000---| :|-----o------||--------
+Vin    |             |/ |     |      ||       |
|              D1      |               0
|                      o  Rotary       0
Cs  -----                    X  Spark        0 Lp
-----                    o   Gap         0
|                      |               0
-Vin    |                      |               |
------o----------------------o----------------

With the insertion of the blocking diode D1 in the charging path, you
can run at varying break rates that are equal or less than:

BPS (Max) = 1/(Pi*SQRT(Lc*Cp))

There are other advantages to resonant charging as well. For one, it can
significantly reduce power arcing, since the capacitor recharging
voltage has a sinusoidal shape, and the capacitor recharging voltage
starts out increasing quite slowly. Alternative recharging approaches
may lead to exponential (via resistive) or linear (via a current-limited
source) voltage increases, and either of these approaches may result in
the rotary gap refiring, resulting in power arcing at low rotary
velocities.

Since the resulting tank capacitor voltage is twice that of the incoming
DC supply, this permits operation from a lower voltage DC power source
for the same bang energy. And, by varying the supply voltage and break
rate, you can obtain consistent control of bang size and power level
going to the coil. Nice approach...

Safe coilin' to you!

-- Bert --
--
Bert Hickman
Stoneridge Engineering
Email:    bert.hickman-at-aquila-dot-net
Web Site: http://www.teslamania-dot-com

```