Demo Coil Protection

[alan sailer]

I have built several tesla coils at this point and have been thinking about
using them as part of an electricity educational talk. My question is about
what king of circuity would be needed to help keep a coil from frying electronics
plugged into the power grid.

I understand a good dedicated ground rod is best but this would not be possible.
I am speculating that there is some sort of commercially available filter that would
keep high voltage transients form feeding back into the  local power circuits.

The power being drawn is 1kW or less. The coil currently has no such protection
 and my garage electrics is just fine. But I hate to give a demo at a local school
and fry their computer system.

Cheers.

[SAMGO]

I have built several tesla coils at this point and have been thinking about
using them as part of an electricity educational talk. My question is about
what king of circuity would be needed to help keep a coil from frying electronics
plugged into the power grid.

I understand a good dedicated ground rod is best but this would not be possible.
I am speculating that there is some sort of commercially available filter that would
keep high voltage transients form feeding back into the  local power circuits.

The power being drawn is 1kW or less. The coil currently has no such protection
 and my garage electrics is just fine. But I hate to give a demo at a local school
and fry their computer system.

Cheers.

You could use a main AC filter like the one in this photo:



I have implemented them in my medium and small tesla coil just for protection but never had the time to test if they actually make any difference.
Probably a bigger and custom filter that point to around the res frequency would be best but also cost. 

[alan sailer]

SAMGO,

Thanks for the reply.

I had kind of given up on any information and decided to go the route you have
described. Two 20 amp CORCOM units. They spec lots of dB attenuation at the
frequencies of my coil so maybe they will be good.

Cheers.

[Zipdox]

I think a counterpoise in addition to the regular ground connection would reduce noise on the ground lines, as well as possible provide a ground strike point.

[alan sailer]

Yes I could try a counterpoise. If I understand how they work it should help.
I'd have to figure out a folding unit to be able to transport it.

Cheers.

[Da_Stier]

Another approach might be a LISN network.
They are normally used the other way around mainly in stuff like EMC testing, to make sure that there is no interference introduced for example from power supplies.
There are several normed versions for different scenarios.

https://en.wikipedia.org/wiki/Line_Impedance_Stabilization_Network

It is of course only a glorified version of a simple net filter like the one SAMGO posted.



Greetings,
Michael

[alan sailer]

Never heard of one. The article you linked to gave a schematic of the low pass filter inside a LISN.
A 50uH inductor is one element and such an inductor for 15 amps cost about 12$.

It's reasonable to consider building one.

Cheers.

[Da_Stier]

It is a rather specific piece of equipment for EMC testing.
They are also insanely expensive, if you buy one from a big manufacutrer (especially if you consider, what is in it).

Dave from the EEV Blog tore one down a few years back, if you are interested.

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Also this is a pretty good article about LISNs in general:
https://incompliancemag.com/article/topology-and-characterization-of-a-dc-line-impedance-stabilization-network/

It's reasonable to consider building one.

Yes, it's a pretty easy thing to try, especially if you don't need it to be all nice and tidy in a shiny box.




Greetings,
Michael