Hi Bill, I so totally agree with your comment about the price of these being a non-issue, all things considered. As long as we're getting the features we need in the sub-$750 range, that is. When it comes down to it, this is meaningful safety and reliability stuff. No slam to the Bolinas crew, but the SunEye is a lettle less important than that. Unless, of course, you shade a certain type of module and the bypass diode fails and the thing ignites.... Then you could make a case for the SunEye being prudent for Disqualification of location, which would mean there wouldn't be a need for the megger on that non-job. Perhaps you could address a couple of aspects that I have questioned for a long time. First of all, is it or is it not true that megger testing an array at 1kV may result in flaky-bias diodes (my term) if polarity of test leads is incorrect relative the array and/or the array wiring is grounded/not grounded during the test? (The root of my policy to NOT megger arrays unless I have specific procedure provided by the mfr... Me no wanna get in a "you meggered it so you don't have a warranty" conversation if ya know of what I speak.) Which of the mainstream module manufacturers are publishing a procedure for megger testing their arrays for use by installers? Are these being published for wet or dry testing? Both? Which of these manufacturers are supplying this documentation in a publicly accessible manner? (Asked quite a few sales reps over the years and only 1 ever produced a document... I have been able to get some from engineers in the factory, but this was generally when I had a big stick to pound on somebody's desk.) Why don't most installers and distributors know this documentation exists or understand the procedure at this point? Yeah, it's one of those thorny issues with me. Maybe we can get our heads together to steamroll a solution to the above. Happy to take the subject up off-list if you like. On to today's question regarding resolution.... When you are measuring an array, why is the resolution so critical? What value or value range do you believe constitutes a Pass on a quality Csi product? How about Asi / CdTe with crappy glass? How about Asi with Tefcel? Wet? Dry? Does your answer change relative the capacity of the array portion under test? Does the answer change with temperature &/or relative humidity? Does the answer change relative test voltage compared to array VOC? What I'm getting at is, unless the minimum "Pass" value is a very low number for the test setup, say 200K - 2M, or has a very narrow "Pass" range, a super-fine resolution shouldn't be that critical. On the few occasions back in the day when I actually meggered arrays, I used an analog megger. Top end range @ 1kV was 250M. My recollection is that these things pulled 15M or better, but I can't really testify to that... Fuzzy memory on the actual values. I'd have to dig through some deep stacks of paperwork to find out if I have any archives of the tests, and I'm not gonna do that for this post. Had to submit the test results to SMUD (can't find them) and the mfrs. Nobody ever said, "Hey. Close your other eye and tell me what it says." When I asked what values would be appropriate, all I ever got was, "Just like you got here. These are good." Never could nail them down and, frankly, never got the idea that they were all-to-happy having installers owning meggers. I'm with you on testing the array and module interconnects for leakage. Really. But, if the arrays rings out as "faulted" when it's really "OK", why bother? What are you looking for? If the resistance is that low, maybe we should be using a "Kohmer" for the arrays and a Megger for the wiring & equpment bussing. If you're getting such a low resistance, aren't you picking it up with a "Static" test... Would the Earth Bond Resistance function of the 1507 & 1503 be sufficient for these situations? http://us.fluke.com/usen/products/specifications.htm?cs_id=35391(FlukeProduc ts) <http://us.fluke.com/usen/products/specifications.htm?cs_id=35391(FlukeProdu cts)&category=HMA(FlukeProducts> &category=HMA(FlukeProducts) This is basically a voltage shot like a megger, but measures resistance in the <20k range. Resolution very nice there! This tester has a gap between 20k & 100k (0.1M). >From a "reasonable resolution" perspective, I think the gap is more like 20k to 2M. Anything over 2M, the 0.1M resolution should be fine. If the array is that close to failing, fail it and tell the mfr to start making some decent glass. They might understand it better this way: 您吸 Dunno. I think it comes down to figuring out what ranges equal "Pass" for the application and going from there. Will look forward to what you find in your side-by-sides later this week. Please do post back. With a basic description of the glass-type, mounting, wire-management, test results and findings, if you can. I'm gonna hang onto my 1520... If anybody wants to see what one looks like with a 100% Battery Level, let me know... I'll hold it up in front of my webcam for ya! No Ground Faults! Matt Lafferty
_____ From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Bill Brooks Sent: Tuesday, April 28, 2009 10:40 AM To: 'RE-wrenches' Subject: Re: [RE-wrenches] To Megger or not to Megger Dave, The issue is definitely resolution. The cool thing about the Fluke 1520 is that it goes down to 0.001MOhms (1000 Ohms). That is the resolution you are looking for. Neither of the current Flukes go low enough. That is why I’m going into the field later this week to see how a 0.1MOhm meter stacks up to finding faults―I have an array with a pesky fault that should make it fun. Many arrays will ring out as a faulted array when, in fact, everything is fine. This is especially true of a-Si arrays with low quality glass. They are very leaky. I’ll keep looking and report back on a recommendation for Christmas shopping. Just to add punctuation to this thread, I always recommend that contractors megger their arrays, because it has saved my butt several times. Also, with exterior wiring systems it is even more important. The problem in the early days is that people would whine about the $600-$1000 price tag. In my opinion, that argument is gone. With contractors routinely putting down $1400 for a SunEye, the value of a good megger is similar and costs less. Bill. From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of David Palumbo Sent: Tuesday, April 28, 2009 7:59 AM To: gilliga...@gmail.com; 'RE-wrenches' Subject: Re: [RE-wrenches] To Megger or not to Megger Matt, “Muggering”, I think that will catch on. The last post, I think, ol’ Uncle Bill Brooks (4/13/09 8:17 PM) had on this topic raised a concern about “not having enough resolution in the low impedance area. PV arrays can have an impedance to ground of a slow as 2kOhms. A resolution of 0.1MOhms will likely not cut it.” Bill went on to say that he had bought a cheaper meter to test out “for fun”. Some of us do enjoy “muggering around”. So my question is. Do the Fluke 1503’s and 1507’s have enough resolution in the low range? Dave From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Matt Lafferty Sent: Tuesday, April 28, 2009 9:56 AM To: 'RE-wrenches' Subject: Re: [RE-wrenches] To Megger or not to Megger RE: Suggested replacements for Fluke 1520 and "pricey meters"... Good News below! Another Wrench sent me a note off-list last night, asking how much a "muggering" would cost. Here's what I sent him: When I got that 1520 it was just over $600. I just checked online and find that it's a discontinued item... Bummer! Fluke recommends the 1587 or the 1507 or the 1503. They also mention the 1577, but it's an ugly stepsister, or maybe a retarded adopted relative, to the 1587. The 1587 is basically a multimeter that also has a <TEST> button to discharge a high voltage shock into the sample under test... It runs about $620 from standard distributors. <http://us.fluke.com/usen/products/Fluke+1587+1577.htm?catalog_name=FlukeUni tedStates> http://us.fluke.com/usen/products/Fluke+1587+1577.htm?catalog_name=FlukeUnit edStates You can get it for $522 here: <http://www.testequipmentdepot.com/fluke/megohmmeters/1577_87.htm> http://www.testequipmentdepot.com/fluke/megohmmeters/1577_87.htm NOTE: It does not test at 10A in DMM mode which means it wouldn't be able to test short-circuit current in strings. Don't bother with the 1577! The 1507 & 1503 are more robust equipment. You can check them out here: <http://us.fluke.com/usen/products/features.htm?cs_id=35391(FlukeProducts)&c ategory=HMA(FlukeProducts> http://us.fluke.com/usen/products/features.htm?cs_id=35391(FlukeProducts)&ca tegory=HMA(FlukeProducts) While they do measure AC & DC Voltages to 600V as well as some lower ohm & continuity work, they are really more tailored to being a megger. The 1503 will suffice for most of what I expect you will get into, but there are some features on the 1507 that might make it worth considering. Mind you, I haven't looked at at price on either yet, so that last comment may just be noises coming out my ass. The 1507 has a Compare function which basically sets up a Pass/Fail value so you can quickly run through repeated tests. This would be useful for doing larger systems where you are testing dozens or hundreds of circuits at a time. For my purposes, I want my guys to think a little more than "Buzz = OK" and I want them to write an actual tested value down on a piece of paper so this is not a big plus to me. The 1507 also does Polarization Index and Absorption Ratios. These are more advanced di-electric tests that you are not likely to need in smaller scale PV. Use of these features would come into play when playing with real high-voltage gear or transformers. Might also come into play on super-sensitive equipment. They might also be used to assess older or aging underground or overhead feeders. The 1507 & 1503 both have an Earth Bond Resistance function which is likely to become more of an issue in the future. This feature lets you test the resistance between a grounding electrode or a grounding electrode conductor and actual earth. Another use for this feature would be to set the output to 1kV, connect the alligator jaw to one of <Insert name of your least-favorite building official here> extremities and use the probe lead as a tongue depressor while you push <TEST>. This feature used to be in a single-purpose tester that ran >$2K. They also both have backlit displays which comes in real handy out in the field. The primary features you want are: 500V & 1kV Test Voltage and 2 Gohms (2,000 Megaohms) or above for the top end of the range. Any of the 3 meet this spec. Well, I just checked prices for the 1503 & 1507 and I'm pleasantly surprised. The 1503 ranges from about $291-$370. Here's the place I found it for $291 <http://www.testequipmentdepot.com/fluke/megohmmeters/1503.htm> http://www.testequipmentdepot.com/fluke/megohmmeters/1503.htm That's marked down from the regular price of $342. The 1507 ranges from about $385 to $500. Here's where I found it for $385... <http://www.testequipmentdepot.com/fluke/megohmmeters/1507.htm> http://www.testequipmentdepot.com/fluke/megohmmeters/1507.htm That's a special price, for you only, down from $454. All things considered if I were in your shoes, I'd go for the 1503. That give you a solid megger that you can dedicate to that purpose for a reasonale muggering. If it were me, in Matt's shoes... Oh, what am I saying? I've already got mine and I just found out I paid too much for it! But I have Battery Check... Neener neener neener! Be safe out there! Matt Lafferty I hope more hands go up on this topic. Thanks for asking, Keith. Peace and Palm Trees everybody, Matt Lafferty
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