RE: [TCML] DC coils

["S&JY" <youngs@xxxxxxxxx>]

Carlos,

 

Great choice to go with DC!  

 

With the usual DC powered Tesla Coil using a charging reactor and De-Q-ing
diode, you have to use a break rate above a certain minimum, or the rotary
spark gap will start power arcing.  You are probably familiar with Richie's
wonderful website, specifically
http://www.richieburnett.co.uk/dcreschg.html#resonant which gives a very
good explanation of DC resonant charging Tesla Coil theory and practice.  A
good side benefit of this scheme is that you end up charging your primary
capacitor to nearly twice your supply voltage.

 

I worked out a better way to do DC resonant charging which I use on my
coils.  With this method, your break rate can be as slow as you want with no
power arcing or other bad effects.  And your break rate can be as high as
you want, subject to the current capability of your DC supply.  A further
benefit is that when your primary capacitor discharges into your primary,
the power supply is completely disconnected from the primary circuit.

 

To do this requires a second gap on your RSG.  The gaps are arranged so that
one gap charges your MMC capacitor through a charging reactor (only needs to
be a fraction of a Henry) and a De-Q-ing diode.  Then the rotor rotates so
that the second gap discharges the MMC into your primary.  Further rotation
repeats the cycle - charge the MMC from your power supply then discharge the
MMC into your primary.

 

DC coils are fun.  You can vary both the supply voltage and the RSG break
rate.  As you can imagine, the higher the break rate, the more "robust" are
the streamers.  For my coils, break rates in the 200-250 range seem to be
the sweet spot for best streamer length vs power input.

 

My HV rectifiers are strings of 1N5408 1000 volt 3 amp diodes with enough
diodes in each string to be rated for roughly twice the highest voltage they
must handle.  They can handle charging current pulses of 30 amps at 400 bps.
This is the least expensive approach.

 

Please let us know how your DC coil works out.

 

--Steve Y.

 

  _____  

From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On Behalf
Of lightningfor@xxxxxxxxxxxxxxxxxxxxxx
Sent: Wednesday, January 26, 2011 3:33 PM
To: Tesla@xxxxxxxxxx
Subject: [TCML] DC coils

 

 

> I am planning to build a rectified 3phase - DC tesla coil with a
variable
> rotary gap to give a variable pulse rate, and I am wondering about the
use
> of the inductor (charging reactor)...
> I can see this is used for several purposes.
> To limit the charging current to protect the diodes and control the
> maximum pulse per second rate.
> Also, to create a high impedance for the HF circuit so it can oscillate
> with out the power supply being a short accross it...
> I can also see that there would be an optimum size (inductance) to best
> match a given pulse per second rate for best performance.
>
> What I am wondering is if it is possable to build a dc coil with a
> variable pulse rate (without changing the inductance).
> For example, a DC coil with a rotary gap with a variable speed drive.
> And what effect does varying the speed of the gap have on the output?

> Has any body had any experience with this?
>
> Thanks,
>
> Carlos
>


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