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Re: [TCML] DC SGTC charging inductor

Thanks for this advice, guess it was too good to be true, MOT's are good for the job and easy to get thank goodness
-----Original Message----- From: Mark X2 
Sent: Saturday, February 23, 2013 9:32 AM
To: Tesla Coil Mailing List
Subject: Re: [TCML] DC SGTC charging inductor

Hi Ted,
you can forget about the fluorescent tube ballasts, they're no good.

I've just tried them in a quick and dirty setup. With more than 1 in
series, it didn't do anything, dc resistance being 15Ohm each

Using just 1 ballast and without any de-Q-ing diodes, it kind of did
something as supposed to. After power was cut off, oscillations were still
noticable for, maybe, 1 additional second.

And, ofcourse, the insulation just doesn't hold up. Even with the inner
turn connected to the core MOT style, the outer windings spark over.

So I, hastily, conclude that fluorescent tube ballasts are not suitable as
charging inductor for a flyback driven TC. For a lower voltage supply with
a bit more current, in series, they might be useable, but it makes more
sense to use a MOT, as you described in the first place.

regards,
Mark


2013/2/18 Mark X2 <susax2@xxxxxxxxx>


So the ballasts (65W each) are worth a try. I'll connect each inner wire
with the core and series them up to find out what happens. No pain, no gain. 


2013/2/18 Tesla <tesla@xxxxxxxxxxxxxxx>


Hi Again

I've never used fluorescent tube ballasts but cannot see why in principle
an array (sized to match the size of the tesla) of these could not be
suitable . I have no idea of their characteristics and how much DC current they will take before they start to saturate, I've some ballast for a 33 
watt tube but not the 4 tube ballasts you have

I suspect they will not support  much DC current and quite a number of
ballast inductors will be needed for a tesla of any size.

I created a test jig in which I could inject DC thru the core of a MOT
while simultaneously measuring the AC impedance of the winding. I have the 
circuit and can send that to you separately, it used quite a number of
external bits to create a DC supply with a very high AC source impedance
and a method to isolate that DC from an AC injection source measuring the
AC component across a small resistance in series with the winding, I needed 
several variacs and inductors and meters to do it. This is how I was able
to determine the saturation characteristics with DC flowing as I adjusted
the MOT air gap and found about 0.3mm was a good compromise still
maintaining high inductance but greatly increasing the DC current the
winding could support before it saturated

Given the free availability of MOT cores and knowledge about how they
perform it may be the easiest way to go.

If time permits I will re-create the test set up and look how a
florescent lamp ballast inductor saturates with DC in it. Given most of
these are for 33 watt tubes and are small I would guess it will only be in 
the region of 100 mA or less before they saturate. I think they will
support your 30 mA system

Saturation occurs when all of the magnetic domains in the iron core
become aligned so if the DC current has already aligned all (or most) of
the available domains in the iron the AC impedance drops rapidly as there
are none left for the AC component to use causing very high resistive
currents to flow in the winding as the inductance value drops due that
saturation.

Regards
Ted L in NZ

------------------------------**------------------------------**
--------------------

-----Original Message----- From: Mark X2
Sent: Tuesday, February 19, 2013 8:26 AM

To: Tesla Coil Mailing List
Subject: Re: [TCML] DC SGTC charging inductor


Thanks Ted,
I might be mistaken, but isn't saturation caused by a too low turns/volt
ratio?
Current will be max 30 mA, depending on the flyback's voltage drop, so no
worries there.
Do you think a series of 4 fluorescent lamp ballast might be any good or a 
waste of time?





2013/2/18 Tesla <tesla@xxxxxxxxxxxxxxx>

 Hi


I suggest using another MOT secondary , Break open the E/I by using a
hacksaw, I put about 0.3mm piece of plastic in there and then glue it
together with a building adhesive like "no more nails"

modified in this way they do not saturate nearly as much and over 1 amp
of
DC is possible. Arraying these in series and parallel combinations to get 
the required  inductance and DC current ability can then be done. I lost
my
measurements of MOT's modified in this way and can only recall the
inductance was about 10 Hy, this is easy to check by exciting the MOT
with
a modest AC voltage (30 to 120)  and checking the current draw. The
inductance will be somewhat less when it is used as a charging inductance due to the DC flowing in the core BUT the gap ensures the inductance does 
not reduce too much

Hope this assist
Ted L in NZ

-----Original Message----- From: Mark X2
Sent: Sunday, February 17, 2013 9:28 AM
To: Tesla Coil Mailing List
Subject: [TCML] DC SGTC charging inductor


Hi all,

I'm experimenting a bit with a small spark gap Tesla coil to get
acquainted
with dc resonant charging.

The HV source is a HVDC tester which has a huge 250W flyback and the
primary cap is a string of 10 942Cs.
For the de-Q-ing diode I intend to use 3 microwave oven diodes in series. 

But I'm going to need some pointers on how to build a proper charging
inductor,
like size, app. number of windings and HV-insulation. Any advice is
welcome, thanks.

Mark
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