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Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
The electrodes are close enough that when i turn the motor of it will spark, but when it spins it doesn't spark right. It will spark then stop than spark again. Here is a video:
Registered Member #1370
Joined: Mon Mar 03 2008, 09:01AM
Location: Finland
Posts: 56
Sees like you'r motor is from old microwave oven fan. IMO it works near line frequency, so could it be that it switches when transformer output voltage is low? Soon it gets back into the right phase and switches on high voltage.
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
So it seems you are learning what beating interference is and why you need to have a synchronous motor to run with AC input...
The low frequency beat you are hearing is exactly the frequency of asynchronous motor's slip, and spark beats as the voltage on the NST gets in and out of phase with gap alignment.
That is generally going to be bad for coil's output and can be bad for the transformer too if tank cap is too close to resonant value.
You might get away with arsg on AC if you use much higher break rate than 2x mains frequency, possibly with collector motor and many electrodes, but this will not yeld best spark length for power input.
For NST's, I think it's still far more practical to just use a static gap.
Some induction motors can be turned into variable reluctance synchronous motors by grinding out two sides of rotor into flat surfaces to introduce an air gap.
This doesn't seem to work with shaded pole motors like shown on video, though.
On side, I avoid using wood as an insulator at all costs, if it gets just a bit moist it becomes a too good conductor for such a high voltage, possibly with fire as a result...
Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
Yes,I know. I am making yet another one with wood again... But i am using a dc motor. I do not need synchronous and by the way, i am using mot resonant charging. I need to start a forum about making a 24 volt variable supply.
Registered Member #1232
Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 881
You might get away with adding another pair of rotating electrodes to the disc in order to double the break rate. It will still beat with the mains line frequency (ie. surge) but not as badly.
BTW. Never test a rotary spark gap connected directly across an NST without the tank cap and a load connected. The forced breaking of the arc caused by an RSG causes a huge back EMF if it is connected directly across a transformer without the tesla cap or some other load connected. (It is okay to test a static gap in this way because the fixed gap length limits the peak voltage seen by the NST.)
I did this by accident about 8 years ago before I realised the cap was disconnected. Firey 3 inch long sparks flashed over the bushings of the NST for a split second before failed internally. It's a guaranteed way to kill the transformer, if you haven't got a good safety gap across it.
Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
Well i just made a dc rotary spark gap powered by a battery and i get the same darn results. It does it a little less but still wouldn't be good for tc. Mabey it will run on dc resonant charging better.
i made a small arsg with a microwave fan motor like that..
i used the "blank" Cd's you get in a case of blank Cd's (the ones that are clear) i used 3 together with 4 electrodes and DC charging and she didn't work...
i think they are just to slow or something...
i now use a cheap angle grinder and a disk of chopping board with 4 electrodes... i don't run her to long so she don't heat up and it works a charm
(this is when i had 8 electrodes it was running to slow so i half em so i could speed her up and help with cooling)
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Problems with arsg.
