Someone earlier suggested contacting Solmetric in Sebastapol: http://www.solmetric.com/contact-us.html
Their PVA I-V curve tracer is a great troubleshooting tool, and they also carry a Megger MIT 430 insulation tester: http://www.solmetric.com/megger-mit430.html Maybe they have a kit (PVA + Megger) that they use in-house that you could rent you for a day? It's worth asking, especially since you are in the neighborhood. On Nov 27, 2012, at 5:32 PM, Robert Nuese wrote: > Thanks to the Wrenches who have offered good advice. > > In answer to several of you who suggested megger testing, > No, I'm afraid I don't own a megger. It had become clear to me that > this might well be a useful tool in my case, but the things are expensive. > I've managed to install pv systems for 10 years without one, so I can't > justify buying one just for this one issue. I also had the impression > that megger testing may be a bit hard to interpret, and perhaps incon- > clusive, especially for someone with no previous experience. > > Now Larry Crutcher has drawn my attention to a Unisolar installation > guide (newer than versions I've got) that gives instructions on how to > use the megger to test a Unisolar installation. This is just what I need. > I'm a bit surprised that the Unisolar techs I'd spoken to on several > occasions about my problems had never talked about megger testing, > or these instructions. > > So, I need a megger, at least temporarily. > > The Unisolar instructions call for the use of the BM21 or other quality > megger. The BM21 is no longer in production. There are a confusing > array of different models available. Can anyone offer suggestions > about other models that would or would not be suitable for my use? > According to the Megger co. website the new model that replaces the > BM21 is the MIT525, which I can buy online for $3,576. Whew! > On the other hand, I gather I can buy a Fluke 1507 insulation tester > for $500. Would that be adequate? Anyway, even at that much > cheaper, for solving one problem in 10 years, it would make more > sense to rent… > > I called a few of the equipment rental agencies in my neighborhood, > but none had ever heard of a megger. > Does anyone have any idea where I could rent one - or is there a > wrench in my neck of the woods (70 miles north of San Francisco) > who would like to rent me theirs? > Or does anybody have a suggestion about a particularly good deal on > buying one? > > Or maybe there is a nearby wrench who I could hire to help, someone > with a megger, who already knows how to use it.? > > Here is a big question. I had assumed that such testing would have to > be done on de-energized circuits, which for the solar panel part would > mean at night. The Unisolar instructions don't mention this. They say > to disconnect each string and then short each out before the test, using > a jumper. This strikes me as odd, and a bit scary. Would it not be > better to do this on a de-energized circuit at night? > > Thanks very much for any further information, > Robert > > > >> Robert, >> >> Having installed hundreds of Uni-Solar modules, the only failure I every >> experienced was a framed US64 that had the PV negative short to frame. >> Flexing the module would create intermittent failure. You have PV laminates >> so your ground fault may be to the metal roof. I might be stating the >> obvious but here's my list of tests: >> >> I would disconnect and hi-pot test each laminate (ref. sec. 4.6, pg 48, >> Installation Guide, AA4-3670-05, 10/05). >> If that does not produce results, apply pressure with a heavy roller up and >> down the edges where the diodes and cell interconnect traces are while >> testing. >> Check all wire penetrations into the channel. >> Make sure all wire expansion rules were followed, look for stressed wire. >> Check for any screws installed in other than the two approved areas. There >> are two versions of laminates. One has a VERY narrow area. 0.65" by 2.75", >> for screw penetration (ref. sec. 3, pg 17, Installation Guide, AA4-3670-05, >> 10/05). A misplaced screw may have allowed water to migrate to the trace >> areas and be providing a path through the screw. >> >> RIP Stan and Uni-Solar, A brilliant mind and the best performing PV's ever. >> >> Larry Crutcher >> Starlight Solar Power Systems > > > > > _______________________________________________ > List sponsored by Home Power magazine > > List Address: RE-wrenches@lists.re-wrenches.org > > Options & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > List-Archive: > http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org > > List rules & etiquette: > www.re-wrenches.org/etiquette.htm > > Check out participant bios: > www.members.re-wrenches.org >
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