Andrew,
As for ballasting using a variable reator with iron wire in a tube, try
asking Phil Strauss on the TCUK mailing list (tcbouklist at yahoogroups
dot
com). He has build a very smart one
tcbouklist@xxxxxxxxxxxxxxx
cheers
Thomas
-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
Behalf
Of andrew
Sent: 29 December 2009 20:20
To: 'Tesla Coil Mailing List'
Subject: RE: [TCML] Advice on MMC
Thanks David
Yes, I have 4 MOTs primaries in parallel at 240v 50hz, secondaries in
series, output voltage, 9200 as far s I can tell.
I fed 24 volts ac into primaries and measured 920 v total accross
secondaries, as turns ratio will be constant. I imagine it will change
under
load though.
Not quite sure how to measure the s/c current though. The ratings of the
microwave ovens were all in the 1300/1400 watt range and 240v 50 hz 6.5
to
7
Amps so I would guess that in microwave operation they would be running 6
amps through the magnitron as virtually a short circuit limited by
resistance and the saturation of the shunted transformers. If that is the
case then my primary current would be in the 20~ 24 amp range. It would
be
more manageable if it were 18 to 20A max and I have tweaked JavaTC to see
how this affects things.
How can I get a more precise answer on s/c current or is this close
enough?
ie how do you measure this? I have a fluke digital meter but I am a bit
leary of shorting out the 9000v secondary lest there be smoke! Is it
really
ok to do that?
And yes regarding Ballast. I think I need something there. At the moment
for
testing things and to stop it blowing fuses. I have just been using a 3
kw
oil column heater in series with the primaries. (very big resistor!)
I don't have a variac but am keeping my eye out for one of suitable
rating
but there are not many for sale around here.
I like the idea of building a variable reator with iron wire in a tube
but
not quite sure how to do that.
Andrew
-----Original Message-----
From: David Dean [mailto:deano@xxxxxxxxxxxxxxxx]
Sent: Wednesday, 30 December 2009 5:37 a.m.
To: Tesla Coil Mailing List
Subject: Re: [TCML] Advice on MMC
Hi Andrew
I guess I did not read your post carefully enough.
Until Chip Ford ask:
He states that he will be using 4 x MOT. In that case, is a terry filter
needed???
In answer to *that* question, my guess would be that a Terry filter is
probably not needed, but a properly optimized Terry filter with the right
number of MOVs for the voltage and possibly increased wattage rating for
the
resistors to handle the extra current would certainly not hurt anything.
Will try to address some of your original questions, comments
interspersed:......
On Monday 28 December 2009 04:48:41 pm andrew wrote:
Hi
I have been using Javatc to help me design my coil. I am currently
trying to decide on the correct capacitance value for the tank cap
but am a little confused about all the different capacitor values
mentioned.
They are:-
Primary Capacitor uF ; I am asuming this is the actual tank cap used.
Yes
Resonant Cap Size, I think this is the capacitance value that
resonates with the transformer at 50 hz.
Yes, if you have 50Hz in New Zealand
Power factor cap size, To correct the PF.
Yes, but that is the mains resonant value for the primary of the
transformer
with the secondary shorted. Informational purposes, actual value required
for any given setup may vary considerably. 1st place a TC is a non-linear
load, 2nd tank cap adjusts power factor during charging part of cycle.
Best
to not use power factor correction unless you really need it, then start
with small value and add incrementally till best result found.
Static gap LTR cap size, Is this the same as the Tank Cap?
srsg LTR cap size. ditto but for a Sync gap.
Yes, these are suggested values for use with a NST to maximize power
throughput while protecting the NST from overvoltage.
I was planning to use an asynchronous spark gap but from what I have
read this is not recommended for coils designed with Java TC,
Asynchronous rotary spark gap is not recommended for coils powered by NST
Java TC is designed for NST coils Probably why you read that
so for simplicity I will go with a multi pipe static gap. My
transformer is 4x MOT. I am building a Terry filter for it.
Fine
Question:
I assume when you say "My transformer is 4x MOT." you mean a stack of 4
MOTs in series to output approximately 9kV open circuit?
Another Question:
Are you using, or planning to use, any external ballasting for the MOTs?
And yet Another Question:
Are you using, or planning to use, a Variac, or other variable
autotransformer to adjust the input voltage to the MOT stack?
What you need to know:
Open circuit voltage (measured is best)
Short circuit current (measured is best) If using external ballast
measurements are made with ballast in place Input that data into the
boxes
marked "Rated V out" and "Rated mA"
in the transformer design section of JavaTC
Know that the MOT is not linear, and the impedance will change depending
on
the applied voltage, so the result you get will only be valid for the
conditions you have used for inputs. If you are not planning to use a
Variac, it should be close enough. If you *are* going to vary the input
voltage you might want to measure your open circuit voltage and short
circuit current at different input levels and recalculate to see if there
are any gross anomalies that might change the value you choose for a MMC
capacitor.
When I know that, I can order my caps for the MMC.
Yep
Many thanks
Andrew Buxton
Newbie Kiwi Coiler
later
deano
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