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Registered Member #2628
Joined: Fri Jan 15 2010, 12:23AM
Location:
Posts: 627
Hello everyone,
Would using mains ground as the RF ground for a DRSSTC secondary yield the same hazards as an SGTC?
Reason im wondering this, is because I have always used a dedicated ground for coils, but I need a good ground. not a "good enough" ground for a DRSSTC, so does the same issues exist as with any coil?
or should I just take the effort to use a deeper grounding rod?
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
I always ended up connecting my coils to mains neutral, , since I don't even have a house grounding system - a terrible practice for electronic devices in my house.
But the reason for this is that any other ground I can practically make is even worse - I don't even have any decent patch of dirt close enough to the garage. Constructing a proper grounding system would require several square meters of metal buried underground, which I never considered practically feasible. I tried using a water tap for ground, but it ended getting so hot that it boiled water in it.
Bad grounding is very likely to just cause large voltage between your secondary base and mains ground/neutral and subsequently fire. I never wanted to risk this so even if I used some other sort of ground, I'd connect it to neutral as well just to eliminate this potential. Lately I've ran my multi-kw SSTC from mains neutral as ground alone.
I'm wondering whether any other people on this forum are engaging such practices?
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Yes, I've done my last two public demos this way.
I connect the secondary base and strike rails all to the ground wire of the cable feeding the coil, and use an EMI filter in the mains feed, and the capacitors in the filter strap the live, neutral and earth wires together as far as RF is concerned. So all three wires become the "RF ground", a similar idea to Marko's use of the neutral.
I try to Faraday cage the coil as much as possible, and bond the cage to the casing of the EMI filter. My reasoning is that any displacement current intercepted by the cage is diverted away from the mains.
Registered Member #1951
Joined: Sun Feb 01 2009, 01:59PM
Location:
Posts: 105
Steve McConner wrote ...
Yes, I've done my last two public demos this way.
I connect the secondary base and strike rails all to the ground wire of the cable feeding the coil, and use an EMI filter in the mains feed, and the capacitors in the filter strap the live, neutral and earth wires together as far as RF is concerned. So all three wires become the "RF ground", a similar idea to Marko's use of the neutral.
I try to Faraday cage the coil as much as possible, and bond the cage to the casing of the EMI filter. My reasoning is that any displacement current intercepted by the cage is diverted away from the mains.
Registered Member #2416
Joined: Sun Oct 04 2009, 04:23AM
Location: Oceanside, CA
Posts: 91
The cage will certainly suppress any air RF interference on TVs and radios. Without a good ground TC's can act as inefficient antennas and interfere with sensitive electronics.
However, constructing a dedicated ground shouldn't be unachievable. I use 8 3" aluminum rods pounded into the earth covering a 2"x2" area. Water the dirt well a few hours prior to make hammering them in easier. Also watering the area before use may improve grounding as well.
Using main's ground is specifically advised against in EVR's book on DRSSTC, just don't do it.
Registered Member #2628
Joined: Fri Jan 15 2010, 12:23AM
Location:
Posts: 627
I also use a filter, several actually, I built a master fitler for my inputs, then I have an isolation transformer for my SMPS, logic, and other low voltage circuits, then 1 final filter for the bridge's power itself.
the bridge shared no common ground with anything, or is even grounded in the first place.
up till now I am using 3 - 3 feet long copper rods, in a traingle, and 1 foot away from each other.
I still have one more question, If I do use Steve's method, and if I where to run my coil from a generator (6.2kW, 120/240V 60Hz) then will this risk damaging the generator itself?
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Gatedbreakdown wrote ...
I still have one more question, If I do use Steve's method, and if I where to run my coil from a generator (6.2kW, 120/240V 60Hz) then will this risk damaging the generator itself?
It shouldn't damage it, but remember that a generator might not be much of a RF ground. The whole point of using the mains is that it's a network of wires that go through your whole house, and bond to the water pipes, even go out into the street, etc. A generator is just a lump of metal sitting there. If you do use a generator I'd recommend you also use the ground rods.
Yes, an EMI filter is one of those things, but they come in all shapes and sizes. On my Mjollnir coil I use a 25 amp filter that is sold as an accessory for an ABB motor drive. I got it on Ebay. For my latest coil I bought a similar filter new from RS (someone else was paying )
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DRSSTC Ground
, since I don't even have a house grounding system - a terrible practice for electronic devices in my house.
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