Differential Expansion

• To: tesla-at-pupman-dot-com
• Subject: Differential Expansion
• From: John Pepper <jspepper-at-lbl.gov> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
• Date: Fri, 22 Oct 1999 20:00:21 -0600
• Approved: twftesla-at-uswest-dot-net
• Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme

Greetings All,

If anyone is planning on winding a secondary coil larger than 6" you
might want to consider the following.   I wound a nice tight 12" x 36"
secondary coil using PVC pipe and #20 magnet wire.  When I took the coil
off the winding fixture the temperature that evening was in the mid
80's.  I stored the coil in an upright position figuring I would start
the coating process in the morning.  The next morning the temperature
had cooled off to about the low 70's.  I noticed my coil had gaps in the
windings with some of the coils actually overlapping.  I was a victim of
differential expansion.  PVC has a larger linear expansion rate per
degree (roughly a factor of ten) than copper.  Although the delta T was
not significant the results were still dramatic.  I was able to sort out
the crossed windings and retention the coil to my satisfaction within a
couple of hours by hand (uhg).   I believe this situation could have
been avoided by either winding the coil during a lower than average
temperature or by coating the coil immediately after winding.

Bigger is better,
-John Pepper

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