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Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Hi, I have some problems with the secondary coil overheating on my VTTC... The winding is ~25cm (10") long, and with just 15cm (6") sparks, the bottom of the secondary gets pretty hot to around 60C. I was planning to get about twice as long sparks, but no way the secondary will survive that. I even put small wooden blocks under the coils to help the cooling, but it helped just a little.
What should I do to make the secondary heat less? Use thicker wire, or thinner? Or something else?
Here are the coil data: Secondary coil 6.3x25.2cm (2.5x10") winding, enameled wire with 0.30 mm outer diameter, ~840 turns Small improvised topload Primary 28 turns of 2.5mm2 (3.6mm O.D.) PVC insulated wire on 11cm (4.3") form, 2200pf tank capacitor (configuration 2: 40 turns 1mm2 2.5mm O.D. wire, 1000pf tank cap) It seems like the heating was less severe with primary configuration 2, but I'm not really sure.
A photo of the coils if it helps: (sorry for the mess on my table )
Registered Member #989
Joined: Sat Sept 08 2007, 02:15AM
Location: São Paulo, Brazil
Posts: 476
I has some similar problem long time ago with an SSTC, but I didnt noticed the heat until the PVC pipe melted when it was running (it was very cool lol)
In my case the problem was the toroid too near of the last turn of the secondary, and the toroid was acting like a short turn increasing much the current flowing on the secondary.
Also, you can try to change the coupling see if make some difference without affecting sparks...
Registered Member #3450
Joined: Sun Nov 28 2010, 05:01AM
Location:
Posts: 61
Your coupling may be too high. I noticed your tickler coil is under your primary, Try reversing them so your primary is lower and your grid coil is on top. You may have to re-tune it like this.
Registered Member #989
Joined: Sat Sept 08 2007, 02:15AM
Location: São Paulo, Brazil
Posts: 476
Yeah, if topload didnt changed, try to lower the coupling. That will change the fres a little bit, but it may be better. (Also it can reduce the current draw from the Valve)
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Ok, what effect will switching the coils have exactly, except lowering the primary a little? I put it like this to avoid strikes to the grid coil and damage to the tube, also the insulation on the primary conductor is thick so it might sustain more voltage.
I may try just raising the secondary a bit, this will have the same effect right?
If that doesn't help, I have some ideas to try how to improve the secondary coil.
Registered Member #3215
Joined: Sun Sept 19 2010, 08:42PM
Location:
Posts: 780
PVC tends to heat with RF frequencies...
transparent PVC is soldered with a 42Mhz RF field, so we could think as you add pigments, optimum frequency decreases, it should be the same with overall rigidity (additives used)
use white PVC or another material, it should behave nicer
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Secondary coil too hot
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