TDU Microwave/Telsa prize / Tesla Coils / Forums

Forums

4hv.org :: Forums :: Tesla Coils

« Previous topic | Next topic »

TDU Microwave/Telsa prize

first previous 2 3 4 5

Move Thread

LAN_403

Part Scavenger

Mon Sept 04 2006, 03:11AM

Registered Member #79 Joined: Thu Feb 09 2006, 11:35AM
Location: Arkansas
Posts: 673

Geez Mike, that thing looks like a pipe bomb.

Tesladownunder

Wed Oct 25 2006, 08:57AM

Registered Member #10 Joined: Thu Feb 02 2006, 09:45AM
Location: Bunbury, Australia
Posts: 1424

I wound a primary and made a secondary from fan wire then tested them on a small NST.

Photo 1 shows the filament winding from the MOT.
Photo 2 shows the stripped winding wound on to the 3 pronged base support for the glass cooking plate in the MO.
Photo 3 shows sparks of up to 1 inch from it from a 4kV NST and a 2 gap static gap.
Photo 4 shows a racing spark and an interturn short

The windings moved and there was overlap causing the short.

Edit: I have now got sparks using a capacitor from the microwave oven. Those are the hard parts, now to arrange current limiting for the MOT somehow. Perhaps add a microwave "ping" and I have my (initial) entry.

1161766648 10 FT15477 Moteslaprizefilamentcoil

1161766648 10 FT15477 Moteslaprizeprimaryconstruction

1161766648 10 FT15477 Moteslaprizeprisectest

1161766648 10 FT15477 Moteslaprizesecracingspark

Tesladownunder

Sat Dec 09 2006, 03:38AM

Registered Member #10 Joined: Thu Feb 02 2006, 09:45AM
Location: Bunbury, Australia
Posts: 1424

Well no one won it. I didn't get the time before Dec 1. However I have done it - just 9 days late. Shown here with 1/2 inch sparks only but best in development has been 1 inch and plenty of scope for improvement with better design.
Here's how:
Power supply is the MOT. This needs current limiting and this is achieved with a 150nF capacitor and the voltage is boosted by a one stage multiplier using the MOT diode to give 6kV peak. Note that power is taken off across the diode not across the cap to get the voltage multiplier effect. Hey what's this about a 150nF cap? Where is that in a microwave oven? Well that is the key to this project. The 1uF 10kV DC mylar and oil cap (that is in all non-inverter MO's) needs to be taken apart and unwound. Lengths of the multilayered dielectric and foil are taken out and cut to length. It took about 10 feet of the windings to make 150nF. This is perhaps only 30% of the total. New electrodes were added.
Tank cap. This is a 1nF cap. The technique is similar but I retained the original electrodes from the cap to use in this section as they were better suited to a high current. Construction of this cap was different in view of the much higher voltage/current and frequency stresses. It used about 30% of the length of the cap windings. The plates were only about 1 foot long by 2 inches, however I used two sections of foil/dielectric between them. The foil was not connected and was kept to equalise voltage stresses. All in all something like 12 layers of mylar and 2 foil layers separate the main electrodes.
Being mylar they do warm up a bit.
Spark gap This is two aluminium electrodes (from the frame of the MO fan) bolted to part of the MO timer circuit board with all the components and printed circuit ground off. It really needs another section to give better quenching.
Primary is the MO transformer 6V winding which is heavy copper. This is stuck on to the 3 legged wheeled frame that the glass food tray sits on and rotates.
Secondary former is the cardboard internal cardboard insulation from the HV cap. It was washed but became a bit soft but still usable.
Secondary windings use wire from the fan motor and less than half was used. The hot glue didn't stick the cardboard former together properly and the windings slipped and overlapped. I have had some interturn shorting (and may still have) so I can't really push the power much without a rewind. No idea how many turns.
Toroid I did try winding lots of turns of wire on the fan blades but it didn't improve the performance. so I just left the metal mesh spacer that sits on the output of the magnetron for a nice colour.

Pics show the plan and sparks close up. Not fabulous performance but the proof of principle is there are plenty of opportunities to do better.

Peter

1165635481 10 FT15477 Moteslaprizecompleteopensetup

1165635481 10 FT15477 Moteslaprizesparksclose

Tesladownunder

Sun Dec 24 2006, 03:43AM

Registered Member #10 Joined: Thu Feb 02 2006, 09:45AM
Location: Bunbury, Australia
Posts: 1424

.. and finally mounted in a microwave oven. Push START to run and STOP to stop or "cook" for as long as you like. (the electronics still work in the MO)

The final result is not that great really as I have blown the 150nF cap twice now and have to unwind it and chop a piece out. The caps certainly get warm. The spark is less than expected for the power increase and I think I have a shorted turn. It should be capable of perhaps 2 inches but a rewind would be a tedious affair - unless someone wants to put up more prize money

It looks odd having the diode across the spark gap but thats how you get the voltage multiplier to get 6kV peak (2kV RMS, 3kV peak and doubled to 6kV).

Peter

1166931837 10 FT15477 Moteslaprizemodoor

1166931837 10 FT15477 Moteslaprizemointerior

first previous 2 3 4 5

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob