nuckolls.bob(at)aeroelect
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 Posted: Sat Jan 03, 2009 4:24 pm Post subject: Follow-up on Carling switch failures. . . |
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At 03:12 PM 1/3/2009, you wrote:
| Quote: | RE JB weld.
I had the same thought yesterday. What I don't know is whether the JB weld will also add some thermal insulation to the joint and cause any excess heating which will lead to the same result as what we're trying to avoid. Those big exposed fast on tabs got to be working as radiators, but how much. Perhaps a dab of JB over the rivet only will have no appreciable affect on overall cooling. |
Vern mentioned something last night that triggered another
thought of my own today. Certainly vibration and bending
moments put these joints at risk for loosening . . . but
lack of gas-tightness increases resistance due to corrosion
too. If you've got some switches to play with, see if the
rivet is of an material that will readily alloy with 63/37 solder.
We know that the brass tab will. If you can get a solder-cap
over the rivet-to-tab interface AND THEN mechanically secure
the tab with JB Weld, we may well have deduced the simplest 'fix'.
| Quote: |
Anybody know the co-efficient of thermal conductivity of JB weld as it compares to copper? The fast on tabs on the switches are probably a copper alloy? |
Heat rejection in a properly functioning switch is not
an issue. Further, more heat is carried away on the fast-on
terminal and wire than is radiated from the small portion
of tab that would be covered by JB Weld. The kind of heat
that accelerates destruction of the switch happens AFTER
joint integrity is lost. Solder+Potting goes to protection
of that integrity.
Bob . . .
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( . . . a long habit of not thinking )
( a thing wrong, gives it a superficial )
( appearance of being right . . . )
( )
( -Thomas Paine 1776- )
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