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Registered Member #54503
Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288
Just a quick question regarding earthing, Im starting to prepare assembly of my coil, and want to ground everything properly. Ive been reading a bit and see its not recommended to use the earth on the mains supply as an earth. I expect this is because it could damage appliances in the house if the strike ring is hit?
What parts can be safely grounded to the mains earth?
I was going to earth the chassis of the variac and the strike ring to the mains, along with the aluminium enclosure that housed the driver board and the heatsink holding the IGBT's.
If the wall outlet earth cannot be used, does this mean i will need to use a separate earthing rod elsewhere in the ground outside?
Registered Member #1403
Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968
Have you searched the forum for this question?
Just a reminder...
Part II: Posting
B. Do your own research. If you intend to ask a question, please make sure it isn't already addressed in the archives, or on the wiki. Also, be sure to perform at least a cursory Google search. Remember, nobody wants to do your homework for you. Show some effort, and the community will repay you in kind.
Registered Member #54503
Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288
Yes, i had been reading a bit as i indicated, and i have not found any definitive answers here or anywhere else.
It appears grounding the Strike rail to the mains earth is a bad idea, and possibly the IGBT heatsink, but what about any other steel enclosures for the logic boards etc?
Anyway, its also impractical for me especially if im taking the coil to different places to use to have to drive a grounding rod into the ground to connect my coil to, and its mostly concrete where ill be using it.
Some people say water pipes are OK, others say they are not, so im really lost here or else i wouldnt be asking. :P
Would be good if there was a proper article on this subject that could be made as a sticky post here, since there are tons of people asking the same question it appears.
It's not a binary answer question, that's why you see no finite answers. It depends on if there are any sensitive equipment or devices connected to that mains branch, and greatly upon the RF impedance of the mains earth. The short answer that's infallible would don't use the mains earth for anything at all and always run a ground rod network with ribbon cable (or impedance equivalent cable) to all points needing earthing. Since most folks won't or can't do that you'll see conflicting results.
Personally I use both mains-earth and dedicated RF ground-rod earth bound together at coil base, and I RF-bypass all mains connectors to each other at multiple points along the mains branch using class-y and class-x RF grade capacitors. I do this because I have sensitive equipment on the same mains branch, and need to operate that equipment in the immediate vicinity of a high powered TC.
Registered Member #54503
Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288
Sigurthr wrote ...
It's not a binary answer question, that's why you see no finite answers. It depends on if there are any sensitive equipment or devices connected to that mains branch, and greatly upon the RF impedance of the mains earth. The short answer that's infallible would don't use the mains earth for anything at all and always run a ground rod network with ribbon cable (or impedance equivalent cable) to all points needing earthing. Since most folks won't or can't do that you'll see conflicting results.
Personally I use both mains-earth and dedicated RF ground-rod earth bound together at coil base, and I RF-bypass all mains connectors to each other at multiple points along the mains branch using class-y and class-x RF grade capacitors. I do this because I have sensitive equipment on the same mains branch, and need to operate that equipment in the immediate vicinity of a high powered TC.
Ok, well i would be using my coil out in the garage or basement perhaps, all concrete floor, i see some videos where people use wire mesh on the ground below the coil and have a strike rod connected to it. I expect they are trying to create an artificial RF ground with it? I was thinking it would be OK if i unplug all my other appliances and computers etc from the house and i should all be OK if i used the mains earth?
Anyway, for my primary strike protection i am putting a capacitor across from the negative rail, to the heatsink as Steve Ward has documented, so expect this heatsink would have to be grounded to complete a path for the current to flow if the primary was struck?
So really if nothing is grounded to the mains, all i have to do is connect everything that should be grounded, eg strike rail, heatsinks, metal enclosures and the base of the secondary and connect this to either a rod in the ground or an artificial groundplane made from mesh?
Do i need much of a rod in the ground, or would a simple tent peg do in most situations?
Registered Member #54263
Joined: Thu Jan 15 2015, 09:54AM
Location: Perth
Posts: 35
As long as your coil gives less than 1m sparks, you can use, as you say, "artificial ground", i.e. large piece of mesh, or just square 2mx2m made of pipes. The higher you go (i mean power and sparks), the better your earthing must be. You may try "artificial ground" and connect it to mains.
Registered Member #6038
Joined: Mon Aug 06 2012, 11:31AM
Location: Salado, TX
Posts: 248
I ground the bottom of the secondary, strike ring, and other strike objects to the mains ground. I like to use in-line RF filters but have never had a problem with this grounding configuration. It allows me to transport the coil to any location (just hope they did a good job on the electrical wiring at the location).
Registered Member #54503
Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288
Graham Armitage wrote ...
I ground the bottom of the secondary, strike ring, and other strike objects to the mains ground. I like to use in-line RF filters but have never had a problem with this grounding configuration. It allows me to transport the coil to any location (just hope they did a good job on the electrical wiring at the location).
Ok, well im planning to transport my coil around a bit myself too,
I expect sparks at least 2M in length with mine if my CM300's can push that without tripping the 10A breaker!
I guess i could add a switch to change between an artificial ground in certain locations? There are some places where i would like to use it, but im a bit afraid i might fry all the electronics and computers etc in the building!
Registered Member #6038
Joined: Mon Aug 06 2012, 11:31AM
Location: Salado, TX
Posts: 248
I run my mobile coil (CM300 brick) at about 40" arc length and it routinely goes over 10A draw even before current limiting kicks in. Hopefully you have a more efficient design.
Registered Member #54503
Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288
Graham Armitage wrote ...
I run my mobile coil (CM300 brick) at about 40" arc length and it routinely goes over 10A draw even before current limiting kicks in. Hopefully you have a more efficient design.
I guess if i add larger bus capacitors that would help? Increasing the VARIAC should help with power factor correction also. Im not sure how efficiency is improved, im going to be using a laminated copper bus on the primary circuit.
Others here have said that peak current usually not a problem, and should not be enough to trip the breaker. The wiring in the house is rated at 20A anyway, so i may just put a 20A fuse in our switchboard. (our mains is 230V, so current will be less than someone on a 120V mains supply)
I see that Loneoceans has made some new coild using CM300 IGBT's and he is running them at 1500A So they must be able to handle that kind of power OK.
I might improve my coil later and make the MMC larger and push the current more. Im planning to run at around 850A on the primary which should give me at least 2M sparks im told.
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Earthing my DRSSTC?
