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Registered Member #62119
Joined: Sun Feb 04 2018, 04:59AM
Location: Cedar Rapids, Iowa
Posts: 136
There isn't a "materials" section on this forum so I posted my question here since it is related to spark gap Tesla coils.
I have a large Tesla coil (6.5 KVA) which uses a RSG (rotary spark gap). The insulating parts of the RSG are made of several different materials. The base is made from a sheet of GP03. GP03 is used a lot on outdoor HV transformers. Many of the support structures, including the rotor, are made of G10. Does any one know what the susceptibility of G10 and GP03 are to UV light as emitted from a spark gap? These materials are about 6" away from the spark gap.
I have been using this RSG for several years now and it has held up well with no problems. While recently inspecting the underside of the base of my TC I noticed that a 4" x 4" section of the PVC secondary coil tube was yellowed because it is in the direct line of sight of the spark gap which is about 12" away. I do know that PVC is highly susceptible to UV light so I plan on shielding that spot with a little bit of aluminum tape. However, this episode got me to wondering about the integrity of the RSG parts which are made of G10 and GP03 parts which are also in the direct line of sight of the spark gap and are much closer. I can see no apparent discoloration.
Do I need to do some king of UV mitigation to those parts? There's not much that I can do about the G10 rotor since it spins at 3600 RPM and must remain an excellent insulator. I also can't use the aluminum tape on the support structures for UV mitigation as I did on the PVC tube because they must insulate against 14.4 KV RMS. I do happen to have a lot of teflon tape which is claimed to be UV-resistant so I could possibly use that if needed.
Not sure what can be done as mitigation, but I know that G10 and GP03 are basically just fiberglass, Garolite / G10 being fiberglass/epoxy, similar in qualities to FR4, while GP03 is fiberglass/polyester, more like is used for automotive and marine applications. Some quick research indicates that polyester does tend to break down somewhat under UV, but considering the amount of fiberglass boats out there, that breakdown must not happen too fast. In contrast, my research indicates that Garolite / G10 WILL break down under UV, one manufacturer saying so outright on their product page. Moreover, it seems that epoxies in general are quite prone to UV degradation.
I'd say let it roll until it won't any roll any longer, then try to rebuild the RSG with GP03.
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Susceptibility of G10 and Gp03 to UV radiation
