Re: Variac controlled inductive ballast - WARNING

• To: tesla-at-pupman-dot-com
• Subject: Re: Variac controlled inductive ballast - WARNING
• From: "Jeff W. Parisse" <jparisse-at-teslacoil-dot-com> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
• Date: Mon, 06 Mar 2000 12:03:02 -0700
• Approved: twftesla-at-uswest-dot-net
• Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme

Gavin,

I haven't noticed this failure mode in the three years that I've been
running
the Model 8J and 9J. We're talking about series inductors that have one
end and the wiper connected only, right?

Has anybody "measured" a voltage on the unused end?

Jeff

> Why? Because of the auto-transformer configuration, the unused portion of
> the winding was stepping up the voltage i.e. applying 240 volts to the
> first quarter of the winding resulted in a voltage step-up of approx 1000
> volts (1:4) in the last portion of the winding. The variacs enamel
> insulation broke down after only 10 seconds at this voltage.
>
> This failure mode may also (theoretically) occur in multi-tapped inductors
> through the auto-transformer action.
>
> Safe coiling,
>
> Gavin Hubbard

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