I have been noticing that several of my Google Alerts have been about using a MOT (microwave oven transformer) in a Joule Thief. These have mostly been Youtube videos of experimenters that have built a JT using a MOT for the coil.
There are a few disadvantages here. First off, the MOT is huge, heavy and for a JT it is a serious overkill. The MOT can handle more than a thousand watts, and the JT needs much less than a single watt. I think a better choice would be to use a 6.3 volt AC, 1 amp filament transformer, which is still overkill but much less than a MOT: it will fit in the palm of your hand without breaking your arm(!)
Another disadvantage brought up in one of the videos is the MOT will give you a nasty shock. The solution given was to put a neon lamp across the high voltage winding, which lights up brightly when the JT pulses it with current.
Then there is the scarcity of MOTs. You can’t find these at your local Radio Scrap store. You have to cannibalize a microwave oven to get one. Why not just do it right and buy a 6.3 volt, 1 amp filament transformer?
In one video he used a neon sign transformer (NST) insted of a MOT. He wound several turns around the core and connected the ends to a speaker. Every time the JT triggered, a click sound would come from the speaker. He showed the brightly lit neon lamp he put across the high voltage winding, which was used to drive the base. The JT could run at a speed that was as low as one click a second.
One important point about the MOT. This is NOT a toy. You can get severely shocked by the high voltage it can produce. Also, it’s easy to take a toroid of say 1 to 1.5 inches and wind a lot of turns on it, and make a coil with the high ratio of turns that will act the same as the MOT. The (ICH) ZJ43615TC from Surplus Sales might be an acceptable choice.
I’ll probably be back with more exciting stories as the JT with MOT adventures continue.