# DC drive progress

```
From: 	L.Robertson[SMTP:LWRobertson-at-email.msn-dot-com]
Sent: 	Sunday, January 11, 1998 11:25 PM
To: 	Tesla Builders
Subject: 	re: DC drive progress

Hi ...

much about the filter, assuming the 2 uF cap would keep the
filters and the Tesla circuit from seeing each other much,but
experiment proves different.

The filter circuit follows :

>-------00000000-----000000-----------0000------> to 2uF cap.
|          |     |
|          |     |
-----      -----   O
----- .005 -----   O gap
|          |     |
Diode      GND--------|----------|-----|
Bridge                |          |     |
-----      -----   O
----- .005 -----   O gap
|          |     |
|          |     |
>-------00000000-----000000-----------0000------> to 2uF cap.
^             ^              ^
^             ^              ^
ignition      2 mH           600 uH
coil          choke
secondary

The ignition coil secondaries measure 6.7 k ohms at DC, and
are well over a Henry. They have a large self resonance at
610 Hz. The whole filter passes basically nothing above 2 kHz.,

The 0.005 uF caps are hopefully lossy, made of pickle jars
with aluminum tape outside, salt water inside.

The safety gaps were put there to protect the diodes from
anything coming back, but have so far never fired, They are
set to 3/8 ".

The 600 uH chokes are 240 turns wound on a 5k ohm 225 Watt power
resistor. I guess the iron wire in the resistor is helping out,
as the free air inductance calculates to < 200 uH.

Here's the rest of the circuit, copied from Bert's post.

<---------------------------------------------------
|              |                            |
|              |                            |
|              |                            |
To Filter      |              o                            o
|   +           \             ||  0.018 uF
Circuit      -----        G1     o---OOOOO---||---------o    G2
----- Vdc                  Lp   ||  Cp      \
|   -          o                            o
2 uF |              |                            |
|              |                            |
|              |                            |
<----------------------------------------------------

Part of the problem may lie in my homemade cap - in order to
cram as much capacity as I was capable of rolling up, I used
an end fed arrangement - resulting in roughly 5 uH of inductance
although the Q on that is low.

I have just recently decided it's time to get two commercial caps.,
and have quotes now from Jensen for \$290 ea. for 0.05 -at- 50 kvDC /
18 kvAC for type OYB ( tobjen-at-inet.uni-c.dk ). (Plus shipping).
and \$375 for Maxwell caps from Surplus Sales of Nebraska ( www.
surplussales-dot-com ). Using one on each side of the primary should
keep everything under control.

I guess if I ever get to retire I'll start a non-profit organisation
to make capacitors for the needy.

Larry R

```