[TCML] First (or maybe 2nd) light on my medium-sized SG coil

bartb bartb at classictesla.com
Sun Apr 20 11:03:31 MDT 2008 

Hi David,

PFC is certainly worth a try. You'll need roughly 280uF of run cap. With 
PFC's, you have to experiment a little for lowest current, but 280uF is 
the ballpark you'll be looking for.

Take care,
Bart

David Rieben wrote:
> Bart,
>
> Well, list member Terry Oxandale drove over from Little Rock this
> evening to pick up the 15 kVA pig that he bought from me. Of course
> we had to fire up my coils while he was here. We first fired up the
> mid-sized coil before we fired off the Green Monster. Terry also
> suggested firing the smaller coil with just one of the .04 uFd caps.
> We tried tapping about where you suggested and she opened up to
> 5 to 6 ft. streamers ;^) Still having a little trouble keeping the 
> current
> draw down to sain limits but it is running even smoother now. She's
> tapped at about 9 turns like you now suggest and this does seem to
> be pretty close to the sweet spot. I am still wondering if I could
> get any significant current draw reduction benifit by adding the proper
> PFC caps in parallel with the input to the PT?
>
> Take care,
> David
>
>
>
> ----- Original Message ----- From: "bartb" <bartb at classictesla.com>
> To: "Tesla Coil Mailing List" <tesla at pupman.com>
> Sent: Saturday, April 19, 2008 6:54 PM
> Subject: Re: [TCML] First (or maybe 2nd) light on my medium-sized SG coil
>
>
>> Hi David,
>>
>> I certainly understand. I've worried about this as well. I'm sure we 
>> all hit the rafters in our garage now and then, but it does make one 
>> worry. I don't have an alarm system or garage opener so I'm good 
>> there. Also, I relayed the lighting wiring. All I have are wooden 
>> rafters, but still, I keep the sparks off of them as much as 
>> possible. Back in MN I put up a ceiling grid. I should probably do 
>> something similar again.
>>
>> Regarding your coil, I must retract my thought's about the 1.5kva 
>> with the static gap at .04uF (it's not ok). BPS is really low with 
>> 0.35" total spacing. You need this spacing to take advantage of the 
>> higher voltage available. However, to accomplish full throttle 
>> operation and a nice bps range, you should be using a 25nF cap size. 
>> This cap size would be ideal for your coil using the static gap and 
>> will give the best performance. It would also tune in a 10.6 turns, 
>> so you could take full advantage of the full primary.
>>
>> 25nF would be a good reason to build an MMC! Perfect size for an MMC 
>> cap! I know you use what's on hand if at all possible (like all of 
>> us), but I wanted to throw that thought out there.
>>
>> The .04uF will work far better than the .08uF with the static gap, 
>> but if you do, best to keep the gap spacing where it is now to get 
>> the bps up. If you increased it for the peak output of the PT, it 
>> would be down around 40 bps which would reap havoc with the 
>> electrical. As a matter of fact, that .08uF size may be a major cause 
>> of the alarm system due to the low bps. Anyway, you should try the 
>> .04uF for giggles (I would try the tap right at turn 9).
>>
>> Take care,
>> Bart
>>
>>
>>
>> David Rieben wrote:
>>> Hi Bart,
>>>
>>> Well, your calculations are probably pretty close to correct
>>> as I have done a bit more "on the fly" tuning and found that I
>>> am getting a bit better of an output with the tap point backed
>>> off 1 to 1 1/2 turns. As I was stating earlier, it seems that I
>>> may have gone a bit large to keep her fettered down with a
>>> 120 volt service. I will gradually try to get all of the bugs out
>>> and maximize the output. The problem that I am running into
>>> is that I am freaking out my alarm system by firing my coil in
>>> the garage and will probably have to get the alarm company
>>> out here to fix it. I've been able to disconnect the power to
>>> the alarm system pad which helps shut her down but I think
>>> the damage is already done as it does not function properly
>>> when I power it back up. So it looks like I'll have to call
>>> the alarm company back out here to fix it ;^( Momma is pretty
>>> aggravated about it, too.  I've already been through this back
>>> during the early days of trying to tune in the Green Monster.
>>> I found that if I fire it outside that it does not cause this pro-
>>> blem and the same goes for the smaller coil. Also, even with
>>> this mid-sized coil, I cannot keep some of the sparks from
>>> hitting the ceiling of my garage with the 8 ft. of overhead.
>>> I get really nervous about ceiling striking sparks and these
>>> also seem to be the ones that were really freaking out the
>>> alarm system. As a professional firefighter with nearly 20
>>> years under my belt and a previous experience of nearly
>>> catching my house on fire from allowing indiscriminate
>>> ceiling strikes, I believe my fears are well founded!
>>>
>>> David
>>>
>>> PS: I was wondering how you fine tune a primary coil when
>>> the tap comes out on one side of the primary and the tap lead
>>> itself will act as an extra primary turn and add its own induc-
>>> tance to the equation.?
>>>
>>> ----- Original Message ----- From: "bartb" <bartb at classictesla.com>
>>> To: "Tesla Coil Mailing List" <tesla at pupman.com>
>>> Sent: Saturday, April 19, 2008 10:00 AM
>>> Subject: Re: [TCML] First (or maybe 2nd) light on my medium-sized SG 
>>> coil
>>>
>>>
>>>> Hi David,
>>>>
>>>> Interesting your at 8.75 turns on the primary. I'm showing you 
>>>> should be nearer to 6 turns. I tried adjusting a lot of things (top 
>>>> load, coil, surroundings, etc.. and still end up around 6 turns no 
>>>> matter what). It's like 30% detuned high on inductance which is 
>>>> pretty extreme.
>>>>
>>>> Well, if my specs are correct:
>>>> Sec = Helical, 6.5" x 28", 22 Awg, 1000 turns.
>>>> Pri = Flat, 9"ID, 25"OD, 11 turns, 0.375 tubing.
>>>> Top Load = Toroid, 6" x 30"
>>>> Cap Size = .08uF
>>>>
>>>> Even if the above primary is off on the ID an inch or so, it's 
>>>> still near 6 turns, so I question the 8.75 turn tune point. But 
>>>> anyway, what I wanted to let you know is that using the 0.04uF cap 
>>>> size is a primary difference of about 2.6 turns, so regardless, you 
>>>> do have enough primary to try it out. My static gap comments remain 
>>>> the same regardless of the 1.5kva power rating (voltage is 
>>>> unchanged, the only thing that changes is bps).
>>>>
>>>> Take care,
>>>> Bart
>>>>
>>>> PS; love to see a pic some time of the coil.
>>>>
>>>> David Rieben wrote:
>>>>> Hi Bart,
>>>>>
>>>>> Yes, you've pretty much confirmed what I pretty much already knew 
>>>>> :^)\
>>>>> 80 nFd is a big honking capacitor for a 120 volt fired coil, bar 
>>>>> none.
>>>>> I do have the option to go to 40 nFd though, since my primary cap is
>>>>> just (2) paralleled .04 ufd, 40 kV units. However, I am already 
>>>>> tapped
>>>>> at about 8 3/4 turns on my primary coil with a total of just 11 
>>>>> available
>>>>> turns so I'm not 100% sure that I would have enough primary coil
>>>>> turns available to tune in with a 40 nFd. cap. I do know that the
>>>>> inductance does tend to increase as the square of the number of
>>>>> turns, though, so 11 turns may still just get me in under the wire
>>>>> with a 40 nFd primary cap.
>>>>>
>>>>> No, my PT is only rated at 1.5 kVa @ 30*C, but as you probably
>>>>> already know, PTs are generally capable of FAR more output
>>>>> than their nameplate rating suggests for relatively short runs in 
>>>>> Tesla
>>>>> coil service.  Mine weighs about 95 lbs. I wouldn't mind actually
>>>>> getting my hands on a 5 kVA rated PT, though ;^)
>>>>>
>>>>> My topload is a homemade 6"x30" corregated aluminum duct
>>>>> toroid that's covered in aluminum tape to add to its rigidity.
>>>>>
>>>>> David Rieben
>>>>>
>>>>>
>>>>> ----- Original Message ----- From: "bartb" <bartb at classictesla.com>
>>>>> To: "Tesla Coil Mailing List" <tesla at pupman.com>
>>>>> Sent: Wednesday, April 16, 2008 8:46 PM
>>>>> Subject: Re: [TCML] First (or maybe 2nd) light on my medium-sized 
>>>>> SG coil
>>>>>
>>>>>
>>>>>> Hi David,
>>>>>>
>>>>>> I got a chance tonight to take a closer look at your specs. I 
>>>>>> assume your PT is in the 5kva range? BTW, what's the top load?
>>>>>>
>>>>>> Your total gap distance is kind of low causing the gap to fire 
>>>>>> early as based on a credit card width of 28 mils (I measured one 
>>>>>> of my own), so the total gap is about 0.2". The gap should be 
>>>>>> firing at about 65 to 70% of a 120Vac source. I personally would 
>>>>>> have set the total gap to be 0.35" in your case (50 mils between 
>>>>>> each electrode). This would allow the gap to arc at near the 140 
>>>>>> Vac available with the variac. But at 140 Vac setting, you will 
>>>>>> have nearly 50 amp spikes occurring on the line. With 20A 
>>>>>> service, you don't want to go over 2500 VA. This forces you to 
>>>>>> run at 1/2 power (or less) and in your case, your breakers are 
>>>>>> forcing this.
>>>>>>
>>>>>> As DC mentioned, you could parallel a couple 120V sources (which 
>>>>>> is not a bad idea). Just because the PT is setup for 120V, 
>>>>>> doesn't mean it should go over 2500 VA on a single source (and it 
>>>>>> is certainly capable in TC service). The cap is large. Reducing 
>>>>>> it only slightly would make things worse (I think your 
>>>>>> transformer resonance is 65nF). You could go to 40nF and run STR 
>>>>>> however. These smaller caps can have big sparks also. My cap size 
>>>>>> is 4.3 times smaller than yours and my sparks are longer! Go figure.
>>>>>>
>>>>>> It's one thing to have a 120V source coil. But big caps require 
>>>>>> power, sparks require power at the bang, and power requires the 
>>>>>> capability of the circuit it's sourcing power from. This coil can 
>>>>>> do so much better, but it is limited by the source. You'll have 
>>>>>> to run at a lower power, consider something like DC suggested, or 
>>>>>> lower that cap size. I think it's just too much transformer power 
>>>>>> and cap size for the 120V line.
>>>>>>
>>>>>> I run a 200mA 120V transformer for the small coil using an 18.5nF 
>>>>>> cap size. But as I said, I watch the current, I keep my feelers 
>>>>>> out for wire heating, and those type of things. I'm required to 
>>>>>> use some common sense considering the house 120V 20A breakers and 
>>>>>> I tend to ride the edge. Your PT is even more capable at 350mA 
>>>>>> current and it's using an 80nF cap size!
>>>>>>
>>>>>> Take care,
>>>>>> Bart
>>>>>>
>>>>>>
>>>>>> David Rieben wrote:
>>>>>>> Hi all,
>>>>>>>
>>>>>>> I have finally gotten my mid-sized SG coil project up and running
>>>>>>> A quick rough-up of the specs are about 28" of #22 AWG magnet
>>>>>>> wire wound on a 6" ID (6.5" OD) white PVC pipe for the secondary 
>>>>>>> coil. The primary is 11 turns of 3/8" copper tubing wound in the 
>>>>>>> classic Archemdian spiral with between 3/8" and 1/2" spacing be-
>>>>>>> tween each turn and the outermost turn has about a 12.5" radius
>>>>>>> (25"diameter). After initial tuning, the primary has been tapped at
>>>>>>> approx. 8 3/4 turns. The transformer is a 120:1 GE potential trans-
>>>>>>> former (14,400 volt output). Ballasting was origianlly going to 
>>>>>>> be via a surplus saturable reactor that was rated at 12 kVA and 
>>>>>>> was origi-
>>>>>>> nally designed to run a bombarder and thus control 240 volts. 
>>>>>>> Naturally,
>>>>>>> I assumed that it shouldn't have any trouble holding the reigns on
>>>>>>> 120 volts input to a PT. However, it seemd that I was having a fer-
>>>>>>> roresonant issue with the saturable reactor in this setup and I was
>>>>>>> pretty quickly tripping the 20 amp panel breaker with only about
>>>>>>> 50 on the dial of the 22 amp Staco variac. The variac would also
>>>>>>> start to make that heaving and humming sound with the start of 
>>>>>>> the SG firing, like it was almost dead shorting.
>>>>>>> So I removed the sat-reactor and replaced it with (2) MOTs with
>>>>>>> their seconadries shorted and their primaries in parallel to 
>>>>>>> each other and of course in series with the 120 volt input to 
>>>>>>> the PT. This does seem to offer better current control although 
>>>>>>> it still seems to start rocking with Staco variac set at 50 to 
>>>>>>> 60 on the dial (very fre-
>>>>>>> quent 50 to 60" strikes to my tool cabinet in the garage). The 
>>>>>>> MOTs do tend to get warm pretty quickly running like this though 
>>>>>>> and I haven't had a chance to pull it outside to "pull the ears 
>>>>>>> back on her" since I am confined for space inside of my garage 
>>>>>>> and the arcs start hitting the ceiling
>>>>>>> if I try to go beyond this (fire hazard, already been there, 
>>>>>>> done that) < :^O
>>>>>>> I don't have any metering on this coil's control panel and the 
>>>>>>> Staco
>>>>>>> variac IS the control panel at this time. Therefore I'm not 
>>>>>>> really sure
>>>>>>> just how much current that it is pulling but I can tell that it 
>>>>>>> is up there a bit. I have at least stopped tripping the 20 amps 
>>>>>>> panel
>>>>>>> breaker since replacing the sat-reactor with the MOTs, though.
>>>>>>>
>>>>>>> O yea, I forgot to mention that the SG is a simple stationary RQ 
>>>>>>> style copper tube gap with (8) 1" diameter x 6" long copper pipe
>>>>>>> segments and the resultant 7 gaps each spaced by the thickness
>>>>>>> of a credit card. The primary cap is (2) paralleled RFI recon 
>>>>>>> mica pulse capacitors, each rated at 0.04 uFd @ 40 kV for a 
>>>>>>> total pri-
>>>>>>> mary C of 0.08 uFd. The topload is a homemade 6" x 30" toroid
>>>>>>> made from two 8 ft. lengths (when fully streched out) of 6" dryer
>>>>>>> duct. Because of the relatively large primary C, I have found 
>>>>>>> that the output is smoother when I short about 2 of the 7 gaps 
>>>>>>> in the
>>>>>>> RQ stationary SG. The gap will start "spitting" with the variac
>>>>>>> is turned to around 30 on the dial instead of 45 or 50 and it makes
>>>>>>> for smoother operation. I almost forgot to mention the the 
>>>>>>> stationary
>>>>>>> SG is forced air cooled by a pretty robust fan (likely several hun-
>>>>>>> dred CFMs). One thing to note is that I just wired the input to the
>>>>>>> fan in parallel with the input to the PT so the more power that 
>>>>>>> I push into the transformer, the faster that the fan will turn. 
>>>>>>> Would
>>>>>>> you all suggest running the fan on a seperate variac or just 
>>>>>>> running it seperately all together and letting her rip at full 
>>>>>>> speed at all times
>>>>>>> the the coil is running?
>>>>>>> I am pleased so far with its performance, but I was wondering if 
>>>>>>> some PFC caps would help to reduce the current draw a bit
>>>>>>> and make sure that I stay within the power draw range of a 
>>>>>>> standard 20 amp circuit on a 120 volt line? After all, that was the
>>>>>>> main reason that I decided to construct this coil in the first 
>>>>>>> place.
>>>>>>> I have about (12) each of some 100 uFd, 370 VAC power factor
>>>>>>> caps that I could cannibalize from another project that I no longer
>>>>>>> have much interest in :^) I'm sure you would love to crunch the
>>>>>>> numbers through your Java TC, Bart ;^)
>>>>>>>
>>>>>>> I could post some pics if Hotstreamer still lets you post photos?
>>>>>>> I have been concentrating so much on the large pig driven coils
>>>>>>> in the last several years that I have just about lost my skills 
>>>>>>> for building sub-pig sized coils <;^)
>>>>>>>
>>>>>>> Thanks,
>>>>>>> David
>>>>>>>
>>>>>>> PS - the primary/secondary coupling is set so that the bottom
>>>>>>> turnof the secondary coil is just about level with the top of 
>>>>>>> the pri-
>>>>>>> mary coil.
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>>>>>>>
>>>>>>>
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