Re: [TCML] Taming the Beast: Inductive Ballast vs. Variac, PFC

["David Rieben" <drieben@xxxxxxxxxxx>]

Hi Jeremy,


----- Original Message ----- 
From: "Jeremy Scott" <supertux1@xxxxxxxxx>

> That sounds interesting, and I may just take you up on
> it. I have another option as well that I'd like to
> explore too. 
>
> I've got 225 amp lincoln arc welder (240VAC@50A input)
> which I was going to use but I have some safety
> concerns. 1) What kind of current limiting will it
> provide at 120V as opposed to 240V and 2) Does this
> work if the welding leads are shorted vs. not? (The
> switching mechanism temporarily breaks the secondary
> welding circuit and I am worried that this will
> translated to 'full blast' if I am running the coil 
> in between clicks.) 


I would assume that Ohm's law would apply and that
the arc welder would limit the current at 120 volts 4X
what it does at 240 volts. Shorting the welding leads 
allows for the maximum current throughput since that's
effectively what you are doing when you weld with it.
Switching the tap selector switch will only disconnect
the power in between clicks, not run at full blast. How-
ever, you will find a label that states to NOT switch
the selector while it's under a load, as this would quick-
ly errode the switch contacts.


> I may settle for it being adjustable only when the
> main power is off, but I really like the idea of
> ramping up slowly by pulling a core. 

This type of welder does not utilize the sliding core to 
adjust the current. There are simply multiple taps.


> Okay now that's interesting. I originally wanted a 
> small 5kV pole pig. But I settled for a PT as an
> intermediate stepping stone from the NST. 
>
> I take it these things are much more robust than the
> typical NST? (Fried my first one, like everyone else
> :) ) Are RC protection circuits on the secondary a
> good thing to have for it? 


Yes, PTs along with pigs are much more robust than 
fragile NSTs and do not require RC circuit protection
although you can still use circuit protection, if desired.
I believe the HV side of all 14.4 kV pigs and PTs are 
rated at 110 kV BIL, so they typically have no problems 
standing up to the nasty kickbacks of a Tesla tank circuit.


> I will probably not run that high a kVA on my coils,
> as I haven't sized the other components for it. (The
> spark gap I'm planning on using is a 120bps 1/4"
> electrode SRSG 'propeller' style with tungsten rods
> and the secondary is a 25"x6.5" form. Caps are going
> to be MMC or a series of one, two or three Maxwell
> .03uf units.)

> From your description of your proposed SRSG design,
I'd say that your coil should easily handle 4.2 kVA. Just
make sure that you run enough strings of your MMCs (if 
you choose the MMC route) to handle the RMS currents.
I woud opt for a (4) sereised-parallel configuration of those 
.03 uf, 35 kV Maxwells (for a total of .03 uFd at 70 kV)
as these have been known to fail from overvoltage with 15 
kV NSTs. This will also spread the RMS currents over the 
4 of them to share the load.

What size toriod terminal do you plan to employ? A good rule
of thumb is to make it about the same demensions of the
secondary coil, which in your case would be 25" x 6.5".


> I have to play with javatc a bit more to figure out
> the specs exactly, and to start that I need to know
> what I can put into it. 
>
>
> Do you have any issues balancing them? For example,
> can one core be left in while the other is out or do
> you have to move them in parallel?

> From what others have stated, balancing is not that big of 
an issue in this situation.


David Rieben
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