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Re: Multi-Mini Transformers
Original poster: "Jim Lux by way of Terry Fritz <teslalist-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>
And, consider the weight of all those transformers (and the structure you're
going to mount them on) and the time to assemble such a complex thing
(granted it's fairly simple, but repetitive.).. Soldering one or two wires
is perceived to go pretty fast, soldering dozens is tedious and seems to
take forever (as I am sure you MMC builders are VERY aware of)
Certainly, if you are buying new parts, one big widget almost always beats
many smaller widgets (be they transformers, transistors, high-power vacuum
tubes, etc.) until you get to a point where the big widget reaches some
fundamental limit: For instance, it's hard to get more than about 100 kV out
of a single transformer at 50-60 Hz, so if you really need 300 kV, you're
going to have to go to some sort of cascade arrangement. (note that this
also applies to MMCs... if you had to pay someone to assemble it, I'll bet
the MMC would cost more than an equivalent performance single package from
Sorrento (Maxwell) or others.)
The fascinating thing about building HV stuff (or almost anything) from
surplus and scrap is that the economics can be turned on its head. You
might be able to get 10 NSTs for a lot less than 1 100kV transformer, so
there's an interesting incentive to come up with clever ways to use lots of
----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
Sent: Friday, June 20, 2003 6:37 AM
Subject: Re: Multi-Mini Transformers
> Original poster: "Stephen Conner by way of Terry Fritz
> At 21:34 19/06/03 -0600, you wrote:
> >Original poster: "Jolyon Vater Cox by way of Terry Fritz
> ><teslalist-at-qwest-dot-net>" <jolyon-at-vatercox.freeserve.co.uk>
> >Has anyone on the List ever used a "multi-mini transformer" approach to
> >implementing a high-voltage power supply for TC use?
> >But looking at this again it appears there may a problem with the
> >interwinding/ core insulation
> >which may be insufficient to withstand the high voltages involved; for
> >with a (non-grounded) voltage of 9600V on the secondary and 240V on the
> >the interwinding insulation on the transformers nearest to the ends of of
> >the "stack" would be stressed by a maximum of (9600-240)/2 =4680 volts.
> >Are mains transformers likely to be rated to withstand this?
> I just got out my Rapid Electronics catalogue and it lists a whole bunch
> mini transformers from 1.5VA to 30VA, all vacuum potted in epoxy and
> claiming 5kV primary/secondary isolation. Therefore you could generate up
> to 10kV centre tapped, if you had the time/money/patience to wire up 42 of
> these little dudes in series :) Using the 3.3VA units, you would get about
> 12mA output. And the transformers cost 3.74 GBP each plus VAT in 40
> quantities. Hardly seems worth it since you could buy a brand new NST for
> the same money :(
> On the other hand, if you were to make a DC supply, you could put a
> doubler on the secondary of each transformer (as Jim Lux suggested) and
> 2*sqrt(2) times the bang per buck. Then you could use DC resonant charging
> to double the voltage again. Hence you could get a 10kV charging voltage
> from 8 transformers, which is a bit more attractive. By centre tapping the
> output, all transformers would be safely within their isolation ratings.
> Since we only need 8, we could go for a bigger transformer, like the 30VA
> 12+12V: 240V unit costing 9.50 GBP. 8 of these would give at least 240
> watts output continuous and could probably be pushed to at least twice
> on short duty. You would connect all the 12V windings in series and hook
> them to the 240V line.
> This would make a pretty mean tabletop coil <evil cackle> but again by the
> time you have bought 8 trannies, 16 450V electrolytic caps, 16 diodes, and
> two charging chokes, you'll have spent more than 100 GBP and got about the
> power of a 12/30 NST.
> Or you could try the little 3.3VA 24+24V:240V units, at 4.15 GBP each. An
> ignition coil would make a perfect charging choke for a little setup like
> this. We are talking bug zapper power though.
> Steve C.