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Re: 48KWATT DRSSTC Warmup
Original poster: Vardan <vardan01@xxxxxxxxxxxxxxxxxxxxxxx>
Hi,
The peak current of the caps is well known and specified. You make a
string, that joins a buss, that joins a larger buss, maybe... No
reason to make a copper buss larger than the primary coil tubing ;-)))
Like little streams joining a river that joins a canal that joins an
ocean... No worries ;-))) It can all be easily worked out. You can
also work out what happens if a cap fails which may actually be worth
while in a large MMC... But the "strings" limit fault current, so it
might be a wash anyway... The bleeder resistors just even the
voltage stress out in a failure. If it's really a bad one, the
skinny leads will fuse it out ;-))
Inductances work down happily too with many parallel strings...
It is probably a matter of cost. But the cost new full rated Tesla
coil caps starts at about $1000... That is like 400 MMC caps!!! I
"know" how to break the single $1000 cap >;-)) But I doubt I could
find the means to seriously break a 400 unit MMC!!!! Maybe run it
over at 90 MPH with the car....
In Christopher's case, the RMS load on the electrolytic buss caps is
probably the concern and not the MMCs... Tip - A piece of cardboard
can easily shield the rest of the electronics and make "cleanup" MUCH
easier if one blows its guts out... But usually, big buss caps fail
rather calmly... They either blow the vent or might blow a quarter
size hole in the side. Fuses and breakers easily kick in fast... Not
a big deal, other than suddenly needing "another" one ;o)) Little
caps are far more dramatic...
MMC still have the advantage that we know very well how exactly hard
we can push them and we can calculate what the stress will be. There
are really no "unknowns" to that... We can easily test them on an
individual basis if we want for a few bucks... They test right spot
on to what we expect and to how they are specified and rated... I
have never seen really valuable good specs for a commercial
cap... Just a bunch of basics and disclaimers.... I wish a
commercial cap would say:
Rated voltage = ? - Easy and they all say that
Maximum short term over voltage = ? - OH!!! Don't do that!!! MMCs
are about 3500V...
300KHz Dissipation = ? Just the same for MMCs since they would not
use poly if it was not a ~100 KHz application... Commercial caps get
all weird on us when such things are asked....
Self healing ? MMCs "EASY"!! Commercial caps tend to need an oil
spill tray...
RMS current = ? Very good info on MMCs... Commercial caps tend to
want to know a lot of if, then, unless, but, stuff... It is a simple thing....
Peak repetitive current = ? A simple connection blowout spec that
very often plagues commercial caps!!!! Cause their internal
connections are often very poor >0:-((
Life (hours) at rated voltage (60 Hz) = ? MMCs at 2kV are 75
hours... Commercial caps require a lot of if, then, unless, but,
stuff... and they really don't know...
Testing... MMC have been around a "long time" and they work
fine. Commercial caps always have that "this "should" work" feel to
them... There are 1000 X more MMC caps out there now than commercial caps....
Of course, 99% of us are NOT going to spend $1000 on a Tesla coil
cap.... A little MMC starts at about $15 ;-)))
Cheers,
Terry
BTW - Very excited to hear of such great DRSSTC work out there :-))))))))
At 08:08 PM 1/25/2006, you wrote:
You know, I've wondered if a huge MMC would do well. I don't worry
so much for the caps themselves, but for the lead and connection
bus. I'm not sure what that limit is before degradation, but there
is certainly a limit.
It will be good test in any event.
Take care,
Bart
Tesla list wrote:
Original poster: Vardan <vardan01@xxxxxxxxxxxxxxxxxxxxxxx>
Hi,
MMC are not really "power level limited". If you stay within the
DC voltage (or just 100% over :o)) they will be fine ;-)) RMS
current is a big factor. Going to 140% of the ratings is usually
the limit, but newer caps seem to handle RMS current better. Just
don't push peak current much!!
If one considers a 10 x 12 array of 14kV RMS and 12 x 13.5 amps RMS
you get a "sustained and rated" 2,268,000 watts!!!! So from that
point of view, 10kW is nuttin ;-)) An overrated "peak" power level
comes out to say 30000V at 7300 amps for about 1/5th of a giga watt :)))
If they get warm, a fan will increase the air dissipation
500%. But it depends on the internal temperature. Poly caps can
take a sustained temperature of 80C for a very long time. However,
that is if internal heating is small. If the internal temp gets to
about 100C, they will blow up...
But really, I would worry far more about the IGBTs than the caps ;-))
Judging from the looks of the coil, it will work perfect!!!
Cheers,
Terry
At 06:56 PM 1/25/2006, you wrote:
The MMC won't take this kind of power level. You will need to run
the big Maxwells like we do on our coils over 6 kVA.
Dr. Resonance
I thought I would share my newest creation, a 10kwatt DRSSTC @
http://users.cableaz.com/~chooper/images/fatboy1wred.jpg .
Since I use plexy, I thought embedding high output UV LED's would be
cool and looks like a spark gap running from the distance @
http://users.cableaz.com/~chooper/images/fatboyblue.jpg .
Little red DRSSTC (ran at the Cheesehead)is in front of new DRSSTC for
comparison, as the 10kwatter is almost 8 feet. 120 caps for the MMC and
is fan cooled as I push my MMC's to melt down....he he. First light is
this weekend.....then off to the 48kwatter DRSSTC...... first step of
the 48kwatter is the 9 foot by 3 foot secondary. 48kwatter DRSSTC will
also use a big, very big MMC; start soldering iron up indeed (maybe 500
caps or so)
Rgs,
Christopher robin