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RE: [TCML] DC coils
Gary, just to clarify, my power supply can only deliver an average of a
couple hundred milliamps continuously. It does have filter (reservoir) caps
in it which can supply the peak currents needed to charge the tank cap. The
filter cap is 24 microwave oven caps in series-parallel.
I don't have a simulator, but it would be interesting if someone that does
would model this setup and report the results.
Steve Y.
_____
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On Behalf
Of Gary Lau
Sent: Thursday, January 27, 2011 8:02 PM
To: 'Tesla Coil Mailing List'
Subject: RE: [TCML] DC coils
Hi Steve,
I think the thing I missed the first time around was - I still had the NST
mindset, with charging currents limited to whatever the NST can deliver. If
your DC power supply can deliver 17 Amps (OUCH!), then this is a whole
'nother story. It still seems very different to charge the cap up in 217
usec, and it's not clear for how long it can supply that current. I didn't
attempt the math, but it now seems at least feasible, and I guess I can't
argue with success ;-)
Regards, Gary Lau
MA, USA
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On Behalf
Of S&JY
Sent: Thursday, January 27, 2011 9:11 PM
To: 'Tesla Coil Mailing List'
Subject: RE: [TCML] DC coils
Carlos & Gary,
What can I say - my setup works wonderfully well - nothing shaky about it!
A twin TC produces connecting 6 ft streamers at 150 bps with an input power
of 1164 DC watts (9.7 KV at 120 mA) which was 1548 VA out of the wall plug.
(My power supply is only roughly 75% efficient since it uses 6 MOTs. A pole
transformer would be better.)
Gary, if you study Richie's site, you can see that the tank cap actually
charges in a half cycle of the resonant frequency of the tank cap and
charging reactor. (Your 99% of the bang interval is true for AC, but not
necessarily true for resonant charging DC systems.) I calculated the time I
had to charge the tank cap was 217 microseconds with my RSG at 400 bps.
This was based on the assumption that the electrodes were close enough for
about a quarter inch of travel past each other for the spark to jump across.
My tank cap measures 41 nF. So the calculated charging reactor inductance
to charge the tank cap in 217 microseconds is 0.116 Henry. The peak
charging current, using 30 KV DC (twice the power supply voltage due to
resonant charging), is 17.8 Amps, but typically I stay below 20 KV. My
charging reactor is made up of 5 air core multilayer coils in series to
withstand the voltage drop across it.
As for losses in the charging gap Carlos, I don't know. The charging gap is
perhaps an order of magnitude less bright and noisy as the discharge gap.
So I believe the losses aren't very much compared to the discharge gap.
Steve Y.
_____
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On Behalf
Of Gary Lau
Sent: Thursday, January 27, 2011 3:18 PM
To: 'Tesla Coil Mailing List'
Subject: RE: [TCML] DC coils
The proposal to charge the capacitor through a second gap seems shaky to me.
In a spark gap, the gap conducts for only a very brief interval (very low
duty cycle), whereas the capacitor typically needs to charge for ~99% of the
bang interval. It can't possibly be charged in the duration that a gap
conducts. What am I missing?
Regards, Gary Lau
MA, USA
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On Behalf
Of lightningfor@xxxxxxxxxxxxxxxxxxxxxx
Sent: Thursday, January 27, 2011 4:48 PM
To: Tesla Coil Mailing List
Subject: RE: [TCML] DC coils
Hi Steve,
Thanks for that.
What would you estimate the losses to be like by charging the capacitor
through a spark gap?
Thanks.
On Wed, 26 Jan 2011 18:43:28 -0700, "S&JY" <youngs@xxxxxxxxx> wrote:
> 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.
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