[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [TCML] large DC coil power supply



Hey Jim,

I suggest that you contact Greg Leyh. He has a 25kW, DC coil at his Nevada Lightning Laboratory, which you might have seen on Mythbusters. I know he's running from three phase power so I'm sure he can offer so insight on power supply design.
Dave
Pleasanton, ca

At 10:02 AM 8/15/2010, you wrote:
I'm looking at various ideas for a power supply for a large-ish DC spark gap coil (let's say, 25kW)... It's an art project, so it's not an income producing widget where you can trade off customer costs. It needs to be portable/transportable without taking days to set up. The basic environment for discussion purposes is a stage or performance setup.. coil on the stage, big heavy stuff (generator, transformers, etc) offstage, separated by some dozens of feet.
This is sort of like the power supply for Electrum, but Electrum was 
designed for permanent installation, and so some of the design 
decisions might be different.  Technology has also marched forward.
Various issues and alternatives for discussion:

How to get prime power in.. You're not going to use 16 gauge cheap extension cords here.
if you want to run off 240 single phase, that's 100A.. bigger than 
one normally plugs into the old dryer socket.
In show business, at this kind of power level, you start running 4 
wire banded (4 separate wires with what are essentially fancy banana 
plugs on the end)

Clearly, this is bigger than typical residential loads, so that means probably using a standalone generator, and in this class, that means 3 phase too, which is nice. So, does one start with 240 or 480?
My gut feel is that 240:14400 transformers are more common (cheaper) 
than 480:14400. And 240V (or 208V) generators are going to be more 
common too (and so cheaper to rent.. in the $100/weekend category, 
it appears).  If you put the HV power stuff near the generator, then 
the fact that you're running BIG wires for the lower primary voltage 
won't be as big a deal, cost wise.  (and if someone is *paying* you 
to run this thing, and they want to put the generator elsewhere, 
then they can *pay* for the rental of the longer wiring)
You've got to get to HV somehow, and the simple way is just to get a 
couple or three pole transformers and run them (open) delta.   25 kW 
@ 15kV is a couple amps, well within solid state rectifier 
territory, especially in oil.
But, 2 or 3 transformers is a "big" package.. (but then, a 25kW coil 
is a big pile o' stuff anyway), and they're oil filled which makes 
transportation a bit more of a hassle.  Do you put them in separate 
road cases? or just one big 1000 pounder?
OR... what about switching power supplies.. Big three phase 
rectifier off the prime power, driving a big power supply (hmm.. but 
you'd probably not be able to find such a power supply 
*surplus/cheap* off the  shelf, unlike you could find pole 
transformers)  And designing and building such a thing is a huge 
project in itself. (compared to a fairly easy 6 pulse rectifier with 
3 transformers or a 12 pulse with 6, which one could lash up in a 
weekend, if you had all the parts)
But maybe there *is* some sort of industry that uses up 20kV 1 amp 
DC power supplies?  (yep.. buy 20 1kW class inverter microwave 
ovens, work out the non-trivial primary isolation issues, and run 
them in series/parallel)
And then, once you've got your DC power.. how do you get it to the 
coil?   It's fairly obvious that the power supply is big and bulky, 
and you're not necessarily going to want to stash it under the 
coil.. so that means running a few amps at 20kV around.. RG213 coax 
should do nicely for that.
_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla
_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla