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Finally Got an MOT

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Firefox

Mon May 26 2008, 04:00AM

Registered Member #1389 Joined: Thu Mar 13 2008, 12:50AM
Location: Pittsburgh, PA
Posts: 346

Well, today I finally managed to get my hands on a MOT, after many conversations with the parents about High Voltage safety and the like. While I did promise to ballast it quite heavily for my first few runs as well as installing weaker protection fuses, but I am allowed to have it (huzzah!), and am now wondering what I can do with it besides powering a Tesla coil, which was my original reason for getting it.

My first instinct was to collect 10 ovens and harvest the caps/diodes to build a one magnitude CW from them, but first I need 9 more ovens (sheesh). I would also like to build a resonant stack after I get a few more ovens. Any suggestions as to good places too look? I'm not out too often on trash nights.

Finally, I am confused by a few thing about my transformer. First, the secondary is connected to the core on one end, is that normal? Secondly, there is a third winding called the 'filament' winding on the MOT according to the service instructions in the case. It seems to be a few windings of a very large gauge wire. What is this winding for?

Arcstarter

Mon May 26 2008, 04:57AM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

Firefox wrote ...

Finally, I am confused by a few thing about my transformer. First, the secondary is connected to the core on one end, is that normal? Secondly, there is a third winding called the 'filament' winding on the MOT according to the service instructions in the case. It seems to be a few windings of a very large gauge wire. What is this winding for?

The winding is always connected to the core because if it wasn't the secondary is so close that it would arc over. Actually i think it is because it will be connected to the frame so you dont need a wire to connect it to the magnetron frame and the diode on the capacitor.

The filament winding ,also known as heater,for future reference, is to heat the filament in the magnetron. Output is normally around 1.5 volts and 6 amps.

Dragon64

Mon May 26 2008, 05:09AM

Registered Member #1438 Joined: Sat Apr 12 2008, 12:57AM
Location: Canada
Posts: 218

When I obtained my first MOT, I just made a simple jacobs ladder out of metal coat hanger. After just a weeks worth of wait, I got my second MO from the garbage dump. I would strongly recommend to make a resonant MOT if you get two MOC's and use the spare MOT as a ballast.

Firefox

Tue May 27 2008, 03:11AM

Registered Member #1389 Joined: Thu Mar 13 2008, 12:50AM
Location: Pittsburgh, PA
Posts: 346

Thank you for the responses. I got the whole thing together today, along with a light socket for ballast, a switch for running w/o ballast (for short runs), a safety switch, and a small Jacob's ladder. With a 100W light bulb in the ballast socket it wasn't all that impressive, but once the ballast was removed, it sure was impressive. I put the cap on the secondary side to keep the amperage down to .8A, which is still 13A on the primary side, a bit high I think.

After all the stuff about safety, my dad was very impressed with the wonderful world of High Voltage. However, I did have one problem, and that was I couldn't get the Jacob's ladder to climb. It would just sit between the two closest points on the wires. Any suggestions on how to make Dr. Frankenstein proud?

Shaun

Tue May 27 2008, 04:28AM

Registered Member #690 Joined: Tue May 08 2007, 03:47AM
Location: New Jersey, USA
Posts: 616

It a little tough to get them climbing with such a low starting voltage. Make sure the rods are as far apart as possible but still arc; if that doesn't work try a very small angle between two straight rods, like a "V" shape but squeezed horizontally.

ea6b607

Tue May 27 2008, 04:50AM

Registered Member #1320 Joined: Sat Feb 16 2008, 01:31AM
Location:
Posts: 67

If your having trouble with that, you can also just start with the two rods about 3/4" apart and pull an arc across the two with a screwdriver (carefully of course) I've noticed that it climbs much easier after a larger arc is formed. Of course this means you have to "trigger" it.

quicksilver

Tue May 27 2008, 03:53PM

Registered Member #1408 Joined: Fri Mar 21 2008, 03:49PM
Location: Oracle, AZ
Posts: 679

I believe the arc climbs from the air warming. I once did an experiment with a Jacob's Ladder covered with a clear tube and uncovered. The covered tube made the climbing very stable it appeared - while uncovered; it didn't want to climb without "help". The air within the tube appeared to warm up and thus helped the movement of the arc.

Myke

Tue May 27 2008, 09:13PM

Registered Member #540 Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969

With a two MOT setup you would want to use four MOCs. Arrange them so that they total 1uF @ 4KV. I think that there has to be four because it decreases the current going through one cap.

For a Jacob's ladder, you might want a third electrode between the two rods to get the arc started. It is called a Gabriel electrode. There is some information on it here.

Firefox

Wed May 28 2008, 02:31AM

Registered Member #1389 Joined: Thu Mar 13 2008, 12:50AM
Location: Pittsburgh, PA
Posts: 346

I was reading the spec sheet on the diode earlier today, and its is a 12kv 500 mA fast diode with a 50ns response time. If I use this diode to half wave rectify my MOT, could I use it directly to power the resonant capacitor in a TC? My planned coil has a secondary with an Fres of 1.25 MHz without a top load and was wound with the 32 gauge wire found on the MO fan. It is 1.625" diameter and 8" long with 833 turns. My primary and tank cap are still being chosen.

Arcstarter

Wed May 28 2008, 03:30AM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

Firefox wrote ...

I was reading the spec sheet on the diode earlier today, and its is a 12kv 500 mA fast diode with a 50ns response time. If I use this diode to half wave rectify my MOT, could I use it directly to power the resonant capacitor in a TC? My planned coil has a secondary with an Fres of 1.25 MHz without a top load and was wound with the 32 gauge wire found on the MO fan. It is 1.625" diameter and 8" long with 833 turns. My primary and tank cap are still being chosen.

Well if you want to power a tesla coil with one mot i would suggest an 811 a vttc. The 811a is easy to use, cheap, and powerful. It takes tuning to keep the 811a cool for longer that 10 second to 1 minute runs, and the mot should have a fan along with the 811a. On ebay you can get a vacuum tube for as cheap as 14 bucks. I bought one for 14 bucks and it worked great! Unfortunately i was stupid so i let the plate grow red for a long time and then put it on cold metal and the glass shattered. I bought 2 for 24 bucks and neither of them have died, regardless that one of them got so red, it glowed so brightly that it made my 5 room lights look like an led! Schematic is here:

As you can see it is very easy to make and all the components cost you maybe 40 bucks. You can use just one vacuum tube, but it will get hotter, by simple omitting one of the tubes and one of the resistors (r1) that was connected to that tube. If you want any help regarding this vttc let me know and i will help you as much as i can!

By the way, a tesla coil will not work with one mot unless you have a few capacitors and diodes to make a tripler or quadrupler and a high voltage tank capacitor, two extra mots for a choke and a rotary spark gap. All that will get you a dc resonant charging tesla coil with just one mot as supply power. check this out.

For this you have to have a dc rotary spark gap because the tank capacitor has to be lower capacitance than what the output would suggest, so you need a rotary spark gap so the capacitor will charge up and discharge right, instead of just making a power arc across a static gap.

If you need i will show you how to make a very simple rotary spark gap with an electric scooter motor or any other motor with about 3000rpm and a nut on the shaft.

Need any thing else let me know!

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