Re: [TCML] DC SGTC charging inductor

[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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