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RE: [TCML] DC coils



Hi Steve, thanks for the info on your system.
Sounds like a solid idea to me...
I am wondering though, about how the change in rotory gap speed effects
the arc length.
In other words, does the charging inductor create a specific speed (BPS)
that works best... Or can you adjust the speed to give different break
rates without the performance being effected too much across the range...?

My other question relates to my input voltage...
My PSU is only good for 10kvdc.
Do you think this would be ok for a large system... (ive never gone dc
before)

Thanks,

Carlos


On Thu, 27 Jan 2011 19:10:46 -0700, "S&JY" <youngs@xxxxxxxxx> wrote:
> 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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