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Registered Member #950
Joined: Sat Aug 11 2007, 02:11PM
Location:
Posts: 8
Recently my TC started arcing between the first few turns on the secondary. It was well varnished. There's no arc between primary and secondary at all.
Is the coupling too tight and creating more volts per turn than the insulation can handle?
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
This is usually a symptom of bad grounding of the secondary. If the secondary isn't grounded properly, you can get a voltage node developing at the base (or really anywhere) which can appear anywhere.
By grounding the secondary base, you ensure that the peak voltage node occurs at the top of the coil.
Registered Member #950
Joined: Sat Aug 11 2007, 02:11PM
Location:
Posts: 8
I use a large ground rod in the earth. The wire to it is thick earth wire but maybe the fac that is is quite long and coiled causes a problem. I will shorten it. Also the contact between RF ground and the base of the secondary is made using an area of copper foil contagting eachother. Maybe this is not a good contact. I will ajust this too.
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
Yes, i would try that first. Remember, if you are getting arcing at the bottom of the secondary (and none to the primary) its because you have a large voltage there, which is due to improper grounding.
Now if you have arcing to the primary as well, than it could be the coupling is too tight as another possibility. In this case, raising the secondary with respect to the primary will decrease the coupling.
Registered Member #1911
Joined: Mon Jan 05 2009, 06:30PM
Location: Salem, Oregon, USA
Posts: 165
Dr. GigaVolt wrote ...
This is usually a symptom of bad grounding of the secondary. If the secondary isn't grounded properly, you can get a voltage node developing at the base (or really anywhere) which can appear anywhere.
By grounding the secondary base, you ensure that the peak voltage node occurs at the top of the coil.
Aren't we looking for a voltage anti-node at the topload? A node would be when the voltage is lowest, so an anti-node would be much more desirable, correct?
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
There should be a zero node at the base where the secondary is grounded (reference point), and a peak voltage node at the topload where voltage is at its maximum. The electrical length between these nodes is 1/4 wavelength. In a half-wave coil (bipolar), you would have the center grounded (zero node) and peak voltage nodes at each end. 1/4 wavelength from the center or 1/2 wavelength from end to end.
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Arcing between first few turns on secondary
