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Re: Question on Primary Lead Heating

Original poster: "James Zimmerschied" <zimtesla@xxxxxxx>

Scott and DrR,
the clips are plated steel (checked with magnet). Being ferrous, I can see where they could be heated by local induced fields. I have since made a new connection from a copper split connector used for heavy gage wire joints. I haven't had a chance to test it yet.

I like the idea of suspending some of the clip parts near the primary to check for inductance heating vs. resistive heating.

It would be interesting to use a thermal camera to see what is hot and what is not.
Jim Zimmerschied
----- Original Message -----
From: <mailto:tesla@xxxxxxxxxx>Tesla list
To: <mailto:tesla@xxxxxxxxxx>tesla@xxxxxxxxxx
Sent: Sunday, August 27, 2006 12:48 PM
Subject: Re: Question on Primary Lead Heating

Original poster: "Scott Hanson" <<mailto:huil888@xxxxxxxxxxxx>huil888@xxxxxxxxxxxx>

Jim -

I'd look for simple explanations like before examining more exotic scenarios.

First, when you say "battery clip", do you mean something like an
overgrown alligator clip?  And your primary lead is attached to this
clip via a small screw?

The localized heating at the clip/lead junction could be simple
resistive heating, with the conducted heat making the first few
inches of primary lead hot.

The great majority of these alligator and battery clips are copper
plated steel, and are not very good for high current applications,
especially at RF frequencies. Also, I'd suspect the clamp screw  for
the primary lead is also just zinc plated steel. First, try
eliminating the screw connection by soldering the primary lead
directly to the battery clip. Make sure the "teeth" of the battery
clip (or whatever makes contact with the actual primary winding) are
bright and clean, and that the spring is strong enough to assure good
contact with the primary.

See if these modifications reduce or eliminate the localized heating.

As another way to explore the "induction heating" theory, you can
support small pieces of different metals (steel, aluminum, copper,
etc) on a small plastic pedestal near the primary. If they get hot,
then there is some induction  heating going on. You can attach a
small liquid crystal "thermometer strip" (used for aquariums) to the
piece of metal to immediately see temperature rise as the coil runs.

Scott Hanson

----- Original Message ----- From: "Tesla list" <<mailto:tesla@xxxxxxxxxx>tesla@xxxxxxxxxx>
To: <<mailto:tesla@xxxxxxxxxx>tesla@xxxxxxxxxx>
Sent: Sunday, August 27, 2006 11:01 AM
Subject: Question on Primary Lead Heating

>Original poster: "James Zimmerschied" <<mailto:zimtesla@xxxxxxx>zimtesla@xxxxxxx>
>I was mentioning that my primary connection wire got hot at the
>point where the lead screws into the battery clip I was using for a
>connector. It also heats in the first inch or so down from this
>connection. When I was first trying to tune the coil, the lead got
>hot enough to melt the insulation on the #12 wire after only a 10-20
>sec run. After finally figuring out where this coil wanted to tune
>(best tune point) the lead still gets pretty warm (hot to touch).
>The thing I found interesting was that the primary coil leads feed
>into a circuit board where they are fed by hook up wire (~#22). The
>primary is about 5 turns of #6 solid copper. The thing that is
>puzzling is that the #22 wires feeding the primary do not seem to
>get too hot. Also the heat sinks on the IGBTs don't get uncomfortably hot.
>My thinking is that the unit is acting like an induction heater, and
>that some point along the primary lead is a node where current is
>high. The hook up wire lengths are fairly short compared to the
>primary tap lead.
>Maybe some others on the list have seen this and can shed light on it.
>Jim Zimmerschied