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grounding wire question

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dmg

Sat Jan 16 2010, 08:00AM

Registered Member #2628 Joined: Fri Jan 15 2010, 12:23AM
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for a tesla coils RF ground, i was wondering what will have the least losses, due to the skin effect, i came up with several options,
-using a flat copper ribbon or ground strap
-using a copper pipe
-using litz wire (insulated strands)
does anyone have any experience or have tried any of these methods?
if so please tell me.

radiotech

Sun Jan 17 2010, 02:24AM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
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Where will the ground wire terminate and what path does this take from the TC low end of the secondary (assumed)?

dmg

Sun Jan 17 2010, 03:13AM

Registered Member #2628 Joined: Fri Jan 15 2010, 12:23AM
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the ground wire will lead to a grounding rod about 1.5 - 2 feet deep into the earth, and the wire will extend 5 feet from the TC's secondary coil, i plan on heavily insulating the conductor to reduce corona (just in case).
hope that helps.
(also i'll probably use 1/2 inch copper pipe for the ground rod rather then solid copper)

radiotech

Sun Jan 17 2010, 04:07AM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
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With this earth rod system not in place, would the low end of the TC return metalically or capacitively to the prime power source, ie the mains power source? Or another way of looking; What is the virtual ground now?

dmg

Sun Jan 17 2010, 05:58AM

Registered Member #2628 Joined: Fri Jan 15 2010, 12:23AM
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the secondary coil is electricly isolated from the primary driver, if that is what you mean, the grounding i am suggesting
involves taking the secondary's lower end termination (provided the other end of the secondary is the topload)
and using a conductor to directly feed the coil's output into the ground.

radiotech

Sun Jan 17 2010, 07:57AM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
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As to skin effect causing resistance losses , I know litz wire is the best at frequencies around 35 kHz, but not from Tesla coil experience, but rather on installing wiring on a induction heater system between the inverters and the work shoes. They were about 12 kW each and there 40 in total. Nothing but the litz would work.
I seem to recall it looked like a #6Awg in size and was soldered on to plugs so the inverter boxes could be pulled if they failed during operation, and repaired ones just pushed in. And if the replacements worked, you knew shortly since they reported back through the same data cable that controlled them.

As to the grounding straps, they too are effective, since we used them, heavy tinned flat braid about 1 inch wide, to bond metal ductwork, that was solidly bolted together with 1/2 inch steel. If the straps were left off assorted 'interesting effects' happened. The ducts housed the conductors, copper pipes that carried the current from the Cottrell precipitator transformer/rectifiers to the gas plates ( a giant capacitor as big as a house that removed the soot from the stack gasses. The system max was 1 amp at 100 Kv. and the controller ramped up the DC until the SPM (sparks per minuet) detector got too high and then retarded it down. The setting of the SPM was in the boiler master loop.

Your ground rod will do some things, it is almost identical to a telephone subscriber earth ground, which is capable of supporting enough current to ring the bell on the earth leg of about a 15 mile aerial line. Also it was the ground return for the lightning protector, that is any voltages, i believe above 400 that can jump the carbon blocks. Telcos recommended those wires be spaced away from other wires on there way to the earth. We installed rods like that, athough used a longer rod, to provide an 'isolated' return for scales that were inspected by the same folks that check calibration of petrol pumps

Tesla , N, Colorado Springs Notes 1899-1900, Nolit, Beograd , 1978.
I imagine coilers have looked at that. Page 37.."possibly the ground affects the primary and the secondary more than assumed..

How tall is your coil?

dmg

Sun Jan 17 2010, 08:14AM

Registered Member #2628 Joined: Fri Jan 15 2010, 12:23AM
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Posts: 627

my coil is still under reconstruction, the last one was a crappy flyback powered coil, so grounding wasn't an issue, but the finished result should stand approximatly 3 feet from the ground to topload and be controlled from a distance, in my DC resonant system, I can estimate about 3 - 4 foot arcs, considering a 12KV 500MA fullwave DC input
and the tank cap will probably see 24kv peaks if i get the system to resonate properly. Ill do the major building during the summer time.
as for the high frequency, I figure most spark gaped coils frequency is in the KHz range, so i think a grounding strap or litz wire might not have too many losses.

thank you for your help.

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