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Registered Member #2115
Joined: Fri May 08 2009, 01:17PM
Location: Singapore
Posts: 46
Hello all, I have just made a solid state tesla coil. Below are some results I have measured:
Clamp meter used: Sountech DCM-307 Values taken 4 meters from the tesla coil, because at the coil itself there was too much interference, causing the clamp meter to show data hold permanantly.
Coil specs: Halfbridge of IRF740s, with 470n filter caps. Supply voltage is rectified 240v mains, can be smoothed with a 330u lytic. Decoupling caps are 2 pcs 1uf 400v DC polypropylene caps in parallel. The coil is almost same as Steve Ward's SSTC5, but there is also CW mode and I used bipolar gate driver chips TC4420 and TC4429. GDT was made from CAT5 ethernet wire and a 3E25 type core (farnell pt: ).
Primary is 20 turns of 18 AWG cable wound directly on top of sec coil (with some layers of plastic inbetween), and secondary is around 1050 turns of 31 AWG magnet wire wound on a 11cm diameter 27cm long PVC pipe. The topload is a semi-toroid with a hemisphere on top. Fres is estimated to be around 310 kHz.
The EMI filter and fuse is only rated for 2 amps, but I dont know why the fuse isnt blowing when i run it on something like fullwave smoothed (fuse is fast).
Questions
-Is the spark output good compared to other SSTCs of similar size? How can i increase it without burning out the weak IRF740s, cos i want the sparks to be longer than the sec coil.. If i increase the coupling by raising the primary coil even by abit, there is corona forming on the top few primary wires.
-I have noticed that the spark output with halfwave rectified, no smoothing is rather short and wispy. I thought the sparks are supposed to be long and sword-like? However, when i make it fullwave unsmoothed, it looks very much like halfwave smoothed- long and sword like, however the current draw is quite high and the fets heat up considerably (see table above). So, is this supposed to happen? is this a problem and how do i fix this?
-I have taped a sheet of aluminium foil on the underside of the plywood board and grounded it to reduce interference to the control electronics. Does this provie a shorted turn to the tesla coil? so should I remove it or will the interference be too great?
-Why is the current draw lower when the coil is making a single ground arc?
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First tesla coil (SSTC)
