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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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