Good question. But i didn't "accurately" measure the charging current
prior to fire wheel mode. What i can tell there was no sign of any change
in sparkgap behaviour. No difference in light output/color or sound. It
happened very sudden.
> When lowering the break rate, the primary current of the supply
> transformer
> decreases. The importand question now is: Did you measure an increasing
> primary current of the supply transformer, just before the ignition of the
> firewheel?
> Or does this happen suddenly without any warning, when the critical bps is
> reached?
>
> ----- Original Message -----
> From: <vam@xxxxxxxxx>
> To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
> Sent: Saturday, January 03, 2015 8:57 AM
> Subject: Re: [TCML] Need some advice on 150kva sgtc
>
>
>>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
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>>>>>>>>>> http://www.pupman.com/mailman/listinfo/tesla
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> _______________________________________________
>>>>>>>>> Tesla mailing list
>>>>>>>>> Tesla@xxxxxxxxxx
>>>>>>>>> http://www.pupman.com/mailman/listinfo/tesla
>>>>>>>> _______________________________________________
>>>>>>>> Tesla mailing list
>>>>>>>> Tesla@xxxxxxxxxx
>>>>>>>> http://www.pupman.com/mailman/listinfo/tesla
>>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> _______________________________________________
>>>>>>> Tesla mailing list
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>>>>>>
>>>>>> _______________________________________________
>>>>>> Tesla mailing list
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>>>>>>
>>>>>
>>>>>
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>>>
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