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Registered Member #1080
Joined: Sun Oct 28 2007, 06:55AM
Location: Northern Ohio
Posts: 4
I want to build a mot powered jacobs ladder. I just scored and old microwave from the seventies and it has to be one of the heaviest microwaves I have ever moved. I pulled the transformer out along with anything else that was good such as the high voltage cap some switches and resistors and other good stuff. I have read alitle into powering anything with mot and realize it needs to be ballasted but was wondering how long I could run the thing if properly setup and how far apart should I place the electrodes. I was also thinking of using the cooling fan from the microwave to cool the transformer. Any help would be greatly appreciated as Im a newbie to this sort of thing although I have been interested in electricity and elctronics for quite some time.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
The easiest ballast for a MOT is to use the HV capacitor in series with the MOT secondary. It also helps the arc length by increasing the "effective" voltage across the arc (sorry I dont know how to say this better). However this is sometimes not enough to properly ballast it.
You will have big difficutly starting the arc as 2kv will not jump more than a mm or so (in jacobs ladder operation) and the arc will most likely be stuck at the bottom. This can be made a bit better by using a center electrode in the bottom of the ladder that is connected to one terminal through a high value HV resistor. You can still start the arc with some insulating stick but I think this is not too practical..
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
See if you can score a second MOT. Connect the primaries in anti-parallel, so the secondaries make a ground centre-tapped 4kV. The extra voltage will make a big difference to starting the ladder. At a pinch, you can use an electric kettle as a primary ballast, but you'll get better results with inductive ballast, like another 2 MOTs (you can never have too many MOTs).
How close to put the electrodes? You can only experiment.
Registered Member #53
Joined: Thu Feb 09 2006, 04:31AM
Location: Ontario, Canada
Posts: 638
I have about 16 mots now, is that too many?
As for close electrodes at the bottom I made it around this problem by attaching a BIG (10megOhm) resistor to a wire halfway between wires at the narrowest section of the ladder. This makes a small "pilot" arc that helps bridge the gap. You can see the resistor in the image below.
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Mot powered jacobs ladder
