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DRSSTC Grounding (Earthing)

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Dylan

Sun Aug 10 2008, 08:30AM

Registered Member #1024 Joined: Sun Sept 23 2007, 10:56AM
Location: Northern NSW, Australia
Posts: 95

I currently run my coils during construction and testing from an isolated 40v supply, with secondary base connected to the supply negative rail.
I have found that if I do not add a small bypass capacitance from the full bridge negative bus to ground I get all kinds of problems with arcing between primary and secondary , and sometimes even arcing noises coming from inside my power supply!
This can be solved by simply connecting one oscilloscope probe to the negative bus, this appears to provide enough bypass to solve the problem.

When I run my coils full tilt I run them directly from a non-isolaing 5Kw variac, and have no such problems with or without the bypass capacitance. I do however always use an inline filter that again provides capacitive bypass from both the live and neutural lines to power ground.

To be honest the grounding of the various areas of the circuit, and the reasons for it, are a bit of a mystery to me.

My question is :

What is the best practice for grounding / ground bypass in DRSSTC's?
Which areas should be grounded or bypassed to RF ground or power ground?

HV Enthusiast

Sun Aug 10 2008, 11:44AM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

Uh, you don't want to connect your secondary base connected to your negative supply rail - thats for sure! Connect it to your 3 prong outlet earth ground. When you operate, the current path on the secondary is from the top and then back to the base again. I usually put a grounding target tied right back to the base of the secondary to keep circulating currents in that loop. If you connect to your power supply rail, all your arc current is just going to back to the base right through that power supply and everything. Not good.

Avi

Sun Aug 10 2008, 11:56AM

Registered Member #580 Joined: Mon Mar 12 2007, 03:17PM
Location: Melbourne, Australia
Posts: 410

Dr. GigaVolt wrote ...

Connect it to your 3 prong outlet earth ground.

wont that blow up equipment in your house?

Ken M.

Sun Aug 10 2008, 02:44PM

Registered Member #618 Joined: Sat Mar 31 2007, 04:15AM
Location: Us-Great Lakes
Posts: 628

Electricity takes the shortest path to ground, and a ground line would be a pretty low resistance and fast wa to get to ground.

Dago

Sun Aug 10 2008, 03:48PM

Registered Member #538 Joined: Sun Feb 18 2007, 08:33PM
Location: Finland
Posts: 181

Avi wrote ...

Dr. GigaVolt wrote ...

Connect it to your 3 prong outlet earth ground.

wont that blow up equipment in your house?

No, thats what everyone does.

HV Enthusiast

Sun Aug 10 2008, 04:56PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

Avi wrote ...

Dr. GigaVolt wrote ...

Connect it to your 3 prong outlet earth ground.

wont that blow up equipment in your house?

Not if you do it right. Yes, there is always risk, but if understand how current flows, its not a big deal. Here are two examples:

BAD EXAMPLE

Wired to your 3rd prong outlet ground. Allowing your DRSSTC to arc to walls, the floor, ceiling. This is bad because currents will flow through your ceiling wiring, pipes, wherever, to find their way back to your secondary ground. This is where devices are most susceptible.

GOOD EXAMPLE

Wired to your 3rd prong outlet ground. But using a strike target which is connected via low impedance connection directly to your base of your secondary or your common ground point on your DRSSTC. In this case, the current from the arc is kept in a very short path, and returned directly to the secondary base. In this case, very little current even "sees" the 3rd prong outlet ground.

But in summary, anytime you run a Tesla coil, there is always the risk to damage sensitive electronics equipment. So be sure to disconnect anything sensitive when running your coils - period!

Estragon

Sun Aug 10 2008, 09:49PM

Registered Member #1391 Joined: Fri Mar 14 2008, 04:49PM
Location:
Posts: 40

But, would more power mean more risk?
Wel, of course, but really much more risk?

Steve Ward

Mon Aug 11 2008, 01:12AM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

I have to agree with Dan on this issue. I run smaller DRSSTCs with mains ground in the house with no issues, i do provide targets for them.

I did have noise problems once when my DRSSTC was allowed to arc to a conduit in the wall, instead of to the RF ground i was using. This is always bad.

I usually draw the line at using mains ground after about 3 foot of spark. Ive seen the ground line potential get high enough to arc over those black terminal strip things to the live 120V line. The extremely bright flash made the event obvious! This was when pushing 5 footers with my 6" diameter coil. Since then ive always kept my RF grounding post distant from the rest of the wiring, just because that ground post connection is not really at 0V, likely a few kV at times.

Dylan

Mon Aug 11 2008, 01:15AM

Registered Member #1024 Joined: Sun Sept 23 2007, 10:56AM
Location: Northern NSW, Australia
Posts: 95

Ok, so secondary base always connected to 'earth' , preferably independant earth (copper stake in the ground or so on), but house wiring earth is kind of okay too, got it.
Strike target connected close to secondary base, got it.

Now what about the Negative rail of the bridge, as this is floating when driven with an isolated supply, should there not be some bypass capacitance to earth here as well?

And also does the same apply to the negative rail of the driver, as it too is otherwise free to float?

And assuming some bypass is wise on the bridge and driver, what value/style , I assume a small X2 class bypass cap?

Thomas

Mon Aug 11 2008, 03:23AM

Registered Member #120 Joined: Fri Feb 10 2006, 07:07AM
Location: Westchester New York
Posts: 83

I don't use the 3rd prone, but i do have my own dedicated ground. I took a 6 foot copper pipe drove it into the ground and routed a dedicated wire from it to my basement. i use this as my ground hook up on my coils. I followed my outdoor outlet on the outside of my garage to the rod in the ground.

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