Percolation II
My copper powder/epoxy experiments have had mixed results (pun intended).
By using copper filings instead of wire bits, I've been able to get good electrical conduction at low currents, at room temperature. When I try high current connections on a solar cell under bright light, the performance starts out almost as good as the silver epoxy, but then falls rapidly to uselessness over ~30 seconds as the cell heats up to operating temperature. If I let the cell cool, then redo the test, the same cycle repeats. By contrast, the commercial silver epoxy suffers a little at high temperature, but not nearly as much.
I'm not sure of the exact mechanism. Maybe the epoxy expands too much with heat, and pushes the copper particles out of contact with each other. It's possible the silver guys use epoxy that's less heat-sensitive.
In any case, I don't currently have spare time to delve into the problem; I've got a solar array to finish and ~two weeks to do it. I'm going to try Josh's idea of bolted/spring contacts, and order a few tubes of silver epoxy as a backup.
By using copper filings instead of wire bits, I've been able to get good electrical conduction at low currents, at room temperature. When I try high current connections on a solar cell under bright light, the performance starts out almost as good as the silver epoxy, but then falls rapidly to uselessness over ~30 seconds as the cell heats up to operating temperature. If I let the cell cool, then redo the test, the same cycle repeats. By contrast, the commercial silver epoxy suffers a little at high temperature, but not nearly as much.
I'm not sure of the exact mechanism. Maybe the epoxy expands too much with heat, and pushes the copper particles out of contact with each other. It's possible the silver guys use epoxy that's less heat-sensitive.
In any case, I don't currently have spare time to delve into the problem; I've got a solar array to finish and ~two weeks to do it. I'm going to try Josh's idea of bolted/spring contacts, and order a few tubes of silver epoxy as a backup.