Working! … and some questions about flashover
Posted: Sat Dec 28, 2013 10:10 amI finally got my oneTesla coil finished, after a few false starts, and thanks to some holiday time.
My 240v kit was missing some parts (diodes, and toroid), which eventually arrived in Western Australia after a detour to Bermuda!
During the final stages I realised I was still missing parts - wire for the primary winding, and the optic fibre. The wire was easy to source, although I think mine is slightly thicker than the original, as it didn't fit in the clip, and was difficult to fit through the supplied pads (eg. for the current sensor). For the optic fibre I bought a 10m Toslink cable for about $3 on eBay and just cut off the end connectors - works fine.
I found that the most challenging part was mounting the secondary coil. On my first attempt the secondary arced down the inside of the tube at about 10% power. After reading some forum posts I:
* erased the massive scorch mark from the inside with the wire-brush attachment on my dremel tool.
* rewired the connections to the end bolts, so that wires inside the tube are as short as possible.
* installed an insulating disk inside the tube (MDF wrapped in rubber) which completely separates the top and bottom sections.
* externally grounded the coil, placing it on a wire mesh that is connected to the bottom of the secondary.
After that it worked fine. Here's a first test using the "Fixed" setting on the interrupter:
http://www.youtube.com/watch?v=OoW69yTSgeY
However, I had some problems while driving it via MIDI. There's quite a lot of flashover on the secondary, which I think may be related to low frequency notes. Does that sound possible? Its only in the lower part of the coil, around the primary, but I'm fairly sure its not arcing to the primary.
Here's a first test using MIDI at about 50% power:
http://www.youtube.com/watch?v=M0DP-hD36JQ
Note that the flashover is completely absent in the first video. There's a bright spot on the bottom left of the secondary, where it seems to be arcing directly between two turns of the winding. Here's a close-up of the spot, which is small but visible due to the surrounding black scorch mark.
Here's another slightly nastier spot.
What should I do about this? Despite the damage, the coil still conducts and is measuring about 230 ohms. Is this problem simply caused by inadequate insulation, or is something else going on? I bought some polyurethane spray, and am planning to do a couple of coats in the hope of improving the situation.
My 240v kit was missing some parts (diodes, and toroid), which eventually arrived in Western Australia after a detour to Bermuda!
bermuda.jpg- (25.34 KiB) Downloaded 176 times
During the final stages I realised I was still missing parts - wire for the primary winding, and the optic fibre. The wire was easy to source, although I think mine is slightly thicker than the original, as it didn't fit in the clip, and was difficult to fit through the supplied pads (eg. for the current sensor). For the optic fibre I bought a 10m Toslink cable for about $3 on eBay and just cut off the end connectors - works fine.
I found that the most challenging part was mounting the secondary coil. On my first attempt the secondary arced down the inside of the tube at about 10% power. After reading some forum posts I:
* erased the massive scorch mark from the inside with the wire-brush attachment on my dremel tool.
* rewired the connections to the end bolts, so that wires inside the tube are as short as possible.
* installed an insulating disk inside the tube (MDF wrapped in rubber) which completely separates the top and bottom sections.
* externally grounded the coil, placing it on a wire mesh that is connected to the bottom of the secondary.
After that it worked fine. Here's a first test using the "Fixed" setting on the interrupter:
http://www.youtube.com/watch?v=OoW69yTSgeY
However, I had some problems while driving it via MIDI. There's quite a lot of flashover on the secondary, which I think may be related to low frequency notes. Does that sound possible? Its only in the lower part of the coil, around the primary, but I'm fairly sure its not arcing to the primary.
Here's a first test using MIDI at about 50% power:
http://www.youtube.com/watch?v=M0DP-hD36JQ
Note that the flashover is completely absent in the first video. There's a bright spot on the bottom left of the secondary, where it seems to be arcing directly between two turns of the winding. Here's a close-up of the spot, which is small but visible due to the surrounding black scorch mark.
- oneTesla-spot-1.jpg
- (62.4 KiB) Downloaded 176 times
Here's another slightly nastier spot.
- onetesla-spot-2.jpg
- (164.84 KiB) Downloaded 176 times
What should I do about this? Despite the damage, the coil still conducts and is measuring about 230 ohms. Is this problem simply caused by inadequate insulation, or is something else going on? I bought some polyurethane spray, and am planning to do a couple of coats in the hope of improving the situation.