FW: Scoped? primary

To: "'Tesla List'" <tesla-at-pupman-dot-com>
Subject: FW: Scoped? primary
From: Tesla List <tesla-at-stic-dot-net>
Date: Wed, 19 Aug 1998 23:42:45 -0500
Approved: tesla-at-stic-dot-net
----------
From:  chris.swinson [SMTP:chris.swinson-at-zetnet.co.uk]
Sent:  Wednesday, August 19, 1998 7:56 AM
To:  Tesla List
Subject:  Re: Scoped? primary


>
>----------
>From:  Harri Suomalainen [SMTP:haba-at-cc.hut.fi]
>Sent:  Tuesday, August 18, 1998 12:20 PM
>To:  tesla-at-pupman-dot-com
>Subject:  Re: Scoped? primary
>
>>>14 turns on this one, I took the free end and connected about 5meg onto
>it
>>>and then went to my probe.  I didn't connect the ground I left it
>floating.
>>
>>to transformer action with the tap you mention.  Be absolutely sure the 5
>>meg resistor will withstand that voltage.
>
>That is really a must. Further, do notice that a properly dc-rated
>resistor
>might not work at ac ringing primary. It may work or may fail in time.
>Reasons behind this danger are related to capasitive effects of the
>resistor
>which may cause uneven voltage stress to different parts of the resistor.
>With large long resistors (hv resistors or long resistor chains) this is
>very
>real. With high-voltage transients this is very likely to cause problems
>sooner or later.
>
>>  The ground lead should be
>>grounded by the scope's ground.
>
>Scope should definately be solidly grounded. A floating scope connected to
>some point of hv circuits might be very dangerous!
>

The scope itself is grounded at the mains plug, but the scope lead itself
was not grounded.  If I did I would get 20Kv down to ground via the scope,
which is not a good idea.


>>  You probably graounded yourself when you
>>touched it and drained you body's charge (you were in the E field of the
>
>5Meg resistor leaks about 2mA at 10kV. You feel that very well.


Humm, The probes don't draw much power from them anyway, so with such a
little load this should not casue a problem.  Though you are very right in
the leeks in the resistors. It did not come to mind first time round.


>Capasitance
>from scope to ground might also be charged to some voltage. Touching
>scope chassis should shock you as well.
>

I only got a shock off the probe ground, I did not get a shock off the metal
case.



All the beST,
Chris.

chris.swinson-at-zetnet.co.uk
www.users.globalnet.co.uk/~mega01/    <--- moved site to...
www.users.zetnet.co.uk/mega.disczine/

>
>
>