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Registered Member #3806
Joined: Sat Apr 02 2011, 09:20PM
Location: France
Posts: 259
As Dr. Slack said this is actually a 2x 5 MOTs stacks in parallel
I've been watching "The Day of the Triffids" yesterday, and I thougt this MOT's stack would be fine for a lethal electric fence to protect against Triffids, zombies and other similar things
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
The MOTs are designed to run with a grounded core. I think that they need to pass a 2KVAC test between the core and primary, so I would consider two MOTs in series on each "leg" acceptable, but not more.
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
Could I suggest the configuration below, unless you *really* need a single ended supply. Many things can be run bipolar, TCs, Jacobs Ladders, general flaming arcs etc. Running it bipolar gives you 2x the terminal to ground voltage between your terminals. All NSTs that I've ever seen are run bipolar with a centre tap.
With only 2 MOTs in series on each leg, OK, you've only got 8kV rather than 10kV between terminals, but you only have 2kV over voltage winding to core on the outer MOTs rather than 8kV overvoltage. If you put 3 in series on each leg, you'd have 12kV between terminals, and still 4kV less over-voltage on your outer MOTs than you have now.
I think I've got the phasing right for 2x voltage, but it's easy to go cross-eyed. My apologies if both legs are the same phase, just swap the polarity on the second leg if it's wrong.
Bear in mind that running it with only 4kV to ground rather than 10kV to ground doesn't make it significantly safer, not enough to change your habits around it when it's powered on. 4kV will still launch itself across a gap to bite you. Think of it as jumping from the 50th floor instead of the 70th.
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
Both schematics posted so far have MOT secondaries connected in series-parallel arrangements.
If they were strictly in series, you could use any mix of scrounged MOT's.
But when two or more secondaries are tied in parallel,
1) The transformers in that group should electrically match each other, and not just in open circuit voltage. That's if you want them to share the load current evenly, and avoid circulating currents in the secondary loop(s).
2) The associated primaries should be hardwired in parallel (not on different switches, or different phases of the mains supply, or opposite halves of split-240 single phase) to reduce the unsafety of the exercise.
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schematic for 12 MOT stack
