I actually played with that alot on a dc coil from a friend. It's a 3 fase
20kva coil without smoothing capacitor (like my big coil). He wanted a
real high bps 900 or so. With the ballast set at discontinues mode for 900
bps he couldn't go below 200 bps. Big flame from the sparkgap en the fuses
popped. No damage done. With the ballast set at 400 bps max he could go
down to 100 bps. It's really a function between charging time and dwell
time.
You could try and test it with fusing the supply very tight. So the fuses
go at 200 bps or so. I have no experience with single fase supplies but i
would definitely take the smoothing capacitor out for this test. With a
smoothing capacitor i would also be very scared to use a low bps.....
> two times the brake rate dropped belowe 150 bps and the fuses popped i'm
> pretty sure that they where firewheel faults.
> I use a 60 cm fr10 disc with 12 slabs of tungsten 5 by 50 by 75mm at 2000
> rpm . stationary gaps are 10mm thick tungsten slabs.
> dwell time must be low with the 5mm contact passing by at roughly 100m/s
> \
> \> Wow, that indeed sounds like a well designed charging reactor for that
>> system! Amazing.
>>
>> Do you have some specs of your rotary also? With 700bps I guess you are
>> using one big disc with at least 10 electrodes to keep the speed and
>> therefore mechanic stress on the disc relatively low. Or are you using a
>> full metal disc + insulating shaft? That would make higher speeds
>> possible
>> with not so much electrodes. What is the diameter of your electrodes?
>>
>> By the way, what is your experience with very low break rates? Did you
>> try
>> out, at which speed the spark gap ignites a "firewheel"? Your reactor is
>> only 500mH so I think low break rates are particulary critical, because
>> the
>> current through the reactor rises at a very fast rate, when the power
>> supply
>> is short circuited accros the closed gap through the reactor and it
>> opens
>> to
>> slow at low break rates? What are your observations?
>> My system is designed for 400bps with a 12,4H reactor, but until now I
>> didn't dare to gow below 200bps altough there where no signs of any
>> problems, I guess I could go even down to 100bps, will have to try this
>> :)
>>
>> Regards,
>> Stefan
>>
>>
>>
>> ----- Original Message -----
>> From: <vam@xxxxxxxxx>
>> To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
>> Sent: Friday, January 02, 2015 6:45 PM
>> Subject: Re: [TCML] Need some advice on 150kva sgtc
>>
>>
>>> Stefan thanks for your observations.
>>> The reactor is wound around a 50 kva 3 fase core with the middle leg
>>> removed. and cut in halve to introduce two air gaps. it has 10 sections
>>> on
>>> both legs with 2.5^2 mmm and 200 turns, so about 2000 turns. i lost the
>>> calculations, but it was the most challeging part to calculate. it will
>>> not saturate.
>>> I'm well aware of the 10 amp charging current.
>>> i choose a large primairy capacitance to compensate for the relatively
>>> low
>>> 32 kv end voltage. i think that's pretty high anyway.
>>> The coil should work nicely at 200 bps and anything above should be a
>>> bonus.
>>> I added a new post with a hopefully working link to a picture of the
>>> coil.
>>>
>>>
>>>> Maybe you have some saturating issues with your charging reactor, is
>>>> it
>>>> designed properly to handle the massive charging current without
>>>> saturation?
>>>> Taking your numbers, that gives a maximum power of 143kW @ 700bps and
>>>> therefore a charging reactor inductance of only 518mH. The RMS
>>>> charging
>>>> current through the choke is 9,9Amps. Designing such an inductor is a
>>>> challenging task, also needs some thick wire to handle 10Amps of
>>>> charging
>>>> current.
>>>>
>>>> Another "problem" I see in your supply transformer, with only 10kV it
>>>> leads
>>>> to big currents, primary capacitance and much to high break rates in
>>>> the
>>>> whole system, for processing the desired power of 150kW. For such a
>>>> big
>>>> system it would be better to use an AC supply voltage in the range of
>>>> at
>>>> least 15 or better 20kV. Your 80kV caps wouln't have any problems with
>>>> that.
>>>> Regarding maximum break rate, different coilers also reported, that
>>>> there
>>>> is
>>>> no big improvement in performance above the 400bps level.
>>>> Regarding spark gap, in my opinion it is better, to not exceed
>>>> 400-450bps,
>>>> but therefore using other tricks to achive a good dwell time and gap
>>>> opening
>>>> speed. By the way, when using more than 4 series gaps in the rotary,
>>>> it
>>>> also
>>>> becomes a problem to "ingnite" the charging system, when using only
>>>> 10kV
>>>> AC
>>>> (~14kV DC).
>>>>
>>>> Regards,
>>>> Stefan
>>>>
>>>> ----- Original Message -----
>>>> From: <vam@xxxxxxxxx>
>>>> To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
>>>> Sent: Friday, January 02, 2015 9:43 AM
>>>> Subject: Re: [TCML] Need some advice on 150kva sgtc
>>>>
>>>>
>>>>> Hi Carlos.
>>>>>
>>>>> The streamer length increases significantly from 100-200 bps. 200-600
>>>>> there is only a slight increase, probably ads only 50-70 cm to the
>>>>> streamer length.
>>>>> The 2.2kw sparkgap motor can't get the disc to spin over 700 bps.
>>>>> The 125 amp fuses can only take 700 bps for a short while before they
>>>>> pop.
>>>>> The coil jumps to two steady streamers at this power level.
>>>>> We had primairy to secondairy flash over at 700 bps, so the coil is
>>>>> in
>>>>> repair now. This led me to believe that the coupling is already too
>>>>> high.
>>>>> It's .2 acoording to javatc. Playing around with the coupling is not
>>>>> so
>>>>> easy with a 250 kilo secondairy and topload. We think about
>>>>> installing
>>>>> a
>>>>> carjack or something like that.
>>>>> The sparkgap quenches at second notch with airstreamers and
>>>>> firstnotch
>>>>> in
>>>>> ground strikes.
>>>>> Highering the coil will probably help some because it easily finds
>>>>> it's
>>>>> way to the floor. We might ad a smaller topload so we can higher the
>>>>> main
>>>>> topload.
>>>>>
>>>>>> It would be intersting to see how arc length would improve if you
>>>>>> lift
>>>>>> the coil up a bit off the ground, and increase the BPS rate.
>>>>>> Coupling is also pretty important on big coils...
>>>>>> Have you experimented with increasing the coupling at all?
>>>>>>
>>>>>> Carlos
>>>>>>
>>>>>> On 2015-01-02 08:13, vam@xxxxxxxxx wrote:
>>>>>>> You got my message spot on Carlos.
>>>>>>> The coil produces constant streamers about 20- 23 feet, or 6 - 7
>>>>>>> meters.
>>>>>>> It's very impressive. But i did make a coil with 1 m winding
>>>>>>> length
>>>>>>> before, producing 3 meter sparks at 20 kw.
>>>>>>> so i expected around 10 meters with this set up. but 7 seems the
>>>>>>> max.
>>>>>>>
>>>>>>>> Big machines like this are typically less efficient than there
>>>>>>>> smaller
>>>>>>>> brothers and sisters.
>>>>>>>> I have not taken the time to run the numbers on the info you
>>>>>>>> provided,
>>>>>>>> but if the system is well balanced and in tune and pulling 40kva,
>>>>>>>> I
>>>>>>>> would expect to see 20-25 foot long arcs at minimum.
>>>>>>>> The height of the coil will also be a limiting factor to some
>>>>>>>> degree...
>>>>>>>>
>>>>>>>> I assume from your question that you are not happy with the
>>>>>>>> performance
>>>>>>>> or it did not meet your expectations?
>>>>>>>>
>>>>>>>> Kind regards,
>>>>>>>>
>>>>>>>> carlos
>>>>>>>>
>>>>>>>> On 2015-01-02 06:03, vam@xxxxxxxxx wrote:
>>>>>>>>> Me and some friends built this coil. It's total height is 5
>>>>>>>>> meters.
>>>>>>>>> the
>>>>>>>>> donut is 2,60 by 60 cm. the coil is 65 cm dia with 1200 turns of
>>>>>>>>> 2.5^2mm
>>>>>>>>> installation wire. about 3.6 meter winding length. Cap, DR
>>>>>>>>> resonance
>>>>>>>>> 100nF, 80kv 4 in parallel.
>>>>>>>>> We feed it with a 180kva 10kv yz5 transformer. Rectify the lot to
>>>>>>>>> 16kv.
>>>>>>>>> ballast ensures 32kv on the cap. at 200 bps we draw 50-60 amps
>>>>>>>>> per
>>>>>>>>> fase.
>>>>>>>>> so roughly 40 kw. Max bps is 700.
>>>>>>>>> Now the question. What kind of spark length should be possible
>>>>>>>>> from
>>>>>>>>> this
>>>>>>>>> coil?
>>>>>>>>>
>>>>>>>>> Picture of the coil.
>>>>>>>>> https://www.facebook.com/photo.php?fbid=671287332969054&set=a.110176789080114.14601.100002633816524&type=1
>>>>>>>>>
>>>>>>>>> _______________________________________________
>>>>>>>>> Tesla mailing list
>>>>>>>>> Tesla@xxxxxxxxxx
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>>>>>>>> _______________________________________________
>>>>>>>> Tesla mailing list
>>>>>>>> Tesla@xxxxxxxxxx
>>>>>>>> http://www.pupman.com/mailman/listinfo/tesla
>>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> _______________________________________________
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>>>>>> Tesla mailing list
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>>>>>>
>>>>>
>>>>>
>>>>> _______________________________________________
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>>>>
>>>> _______________________________________________
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>>>
>>>
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