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Re: [TCML] SRSG "sputter"
Yeah, Gary - I've been thinking about that 40nf number since you first told me about it. I'm at 25.5nf now.
By the way - I had gone back down to 18nf just for the heck of it and the stuttering/sparking goes away. But it makes me nervous because I know the RIGHT number is 28nf. So I go back to my 25.5nf setup and, bang bang bang.
Basically I have to make 2 more boards of 18 to get to 40nf, roughly. I think I may have enough caps. Have to check.
Then I have to figure out where I'm going to mount them...
I also have finally cut a 7" circle of G10 with the Jasper/spiral-drill-bit-on-router method. Sure is messy as hell and I sit here covered in G10 dust, probably a candidate for some sort of cancer, along with the ozone-related lung problems - damn - I'm breathing a lot of ozone these days. And the edge of the G10 circle (in my case) is not ultra precise, but it will do. It seems to provide enough clearance on either side of the 5sK25A-AUL motor.
I had an interesting time figuring out how to mount the disk to the motor shaft. My current theory is to use a 6412K13 3/8" shaft collar from McMaster Carr, and a 4568A22 Arbor mandrel that also has a 3/8" shaft. It's got a 1/4" mounting hole. I drilled a 1/4" center hole in the G10 circle and with a lock washer fastened it to the mandrel, and then the mandrel to the collar, and then the collar to the motor shaft....and then UH OH -
even though all the mechanical drawings for the Oriental Motor 5SK25A-AUL show a 3/8" shaft - it's not. It's about 2mm larger. I did measure it with my micrometer and it came out too large - but I figured I was holding the motor or micrometer wrong - doubted my own eyes - So the shaft collar doesn't fit.
BUT -
Lucky for me I have an almost-shiny new Grizzly G4002 lathe sitting in the corner, and a small boring bit in the tool box. (I know what you're thinking....oh suffer the fools unto me...) So I commence to try to figure out the feed/speed for that kind of thing - can't figure exactly - wing it - bore it, slightly. Now how the heck do you measure 2mm exactly with a tiny boring bit with a lot of flex when everything on the lathe is english? Well you do it by trial and error - error mostly because I've taken exactly 1 3-hour course on Lathe Operations, and barely know how to use the thing. Yes, I know. Beware the tool junkies. Lots of hardware. Not so much brains.
So now I have 2 shaft collars that are about 1/16 too big, and I have to tighten down on the set screws to get them to fit, and, uh no, nothing is concentric anymore. So it's back to McMaster Carr for a couple more of those puppies while I try to figure out how to shim the shafts to make them concentric.
Meanwhile, I'm trying to figure a clever way to mount the stationary electrodes for the new SRSG...I have some HV insulating material on the way. Maybe I'll try making a propeller gap in the interim. That should require no machining...
Alas, the trials of a tyro coiler. (This is what it means to be a coiler, right?)
Joe
On Jul 8, 2010, at 6:01 PM, Gary Lau wrote:
> Awww - where's your sense of adventure ;-) ?
>
> But seriously, component values in Tesla coils are anything but written in
> stone. The only thing that's inflexible is that the primary resonance must
> match the secondary resonance. Beyond that, most things are negotiable.
>
> For a 15/60 NST at 60Hz mains and a 120BPS SRSG, the cap value recommended
> in "the book" is .028uF. But I performed a set of experiments in 2004 (see
> http://www.pupman.com/listarchives/2004/April/msg01087.html) to determine
> which cap value would give me the highest power throughput when I powered my
> NST with a Variac'ed up ~144VAC boost. Using the halogen bulb dummy load, I
> measured the bang voltage at the best SRSG settings, and calculated the
> power throughput for each of cap values .02, .03, .04, and .05uF. The value
> .04uF gave the highest power throughput, so that's what I use in my coil.
> The characteristics of my NST at the elevated voltage may not work for other
> NST's, but it is what it is, and I'm grateful for it.
>
> If the standoff voltage rating of the SRSG is being exceeded, using a higher
> cap value would reduce the maximum voltage, so that may be something worth
> trying. Whether it will improve or degrade the power throughput can't be
> predicted without measurement. But since arcing between the primary circuit
> and motor could be damaging to the motor (and quite possibly everything in
> the house connected to the same power mains as the motor), I would fix the
> gap geometry so it can't arc to the motor.
>
> Regards, Gary Lau
> MA, USA
>
> On Thu, Jul 8, 2010 at 6:47 PM, Brandon Garretson
> <garretsontech@xxxxxxxxx>wrote:
>
>> I would think it best to keep the capacitance within +/- 10% of whatever
>> TeslaMap or JavaTC recommend for your power supply and gap type.
>> That should give you optimal use of your input power and make tuning
>> easier.
>>
>> On Thu, Jul 8, 2010 at 5:42 PM, Joe Mastroianni <joe@xxxxxxxxxxxxxx>
>> wrote:
>>
>>> ""I have run the gap on the NST alone and there's no issue then. But not
>>> with only part of the primary circuit.
>>>
>>> I am now thinking to try Johns theories about the back ring arcing. *I am
>>> also wondering if I should try to increase my mmc capacitance.""*
>>>
>>> **
>>
>>
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