Thanks for the flowers, Drake and Brian. Yes, I'd use PWM without MPPT. We have long jokingly referred to the C40 as "our best selling used charge controller" because of how many we removed once reliable MPPT units (the RVPP/now Blue Sky SB series) hit the market. It was a cost-effective upgrade for anyone who lived on PV in winter. The old C40 (especially the older US-made ones) were reliable and effective, and most are still in service, second time around.
By the way, I just pulled one of these out yesterday - want it at a good price?... and a Rev. 1.0 SW4024 that had never been opened up for service in 15 years, as the ten screws on the back of the earliest units were still intact. I'll put in a 4.01 chipset and someone else can use it for another 15 years. And remove the ten screws. And since it's Friday, and I'd be relaxing now with a beer after the week's work if I only had one, here's a fun (for Wrenches and solar nerds) piece I sent to someone north of here who had done his own off-grid system using mail-order components. I haven't seen the system, but we often talk on this list about the role and benefit of the professional installer, and how the days of home-grown PV systems have pretty much passed - the systems are way more sophisticated and complex these days, and too easy to mess up. He did his own 48V Outback system, and told me he used Sanyo modules, which piqued my curiosity, so we talked about them. Then later I sent him this email: "Mr. ---, When we spoke, I had asked numerous questions about your use of Sanyo modules in an offgrid application, as I had long ago reviewed them and determined that they were't a good fit for battery charging, then promptly went on, forgetting why I'd made that decision. Today I was reviewing module specs for another job. I looked over Sanyo specs and realized why I don't use them: they can't be used correctly for 48V systems, and can only be used in 24V systems if wired in parallel. Your modules aren't appropriate for your application. Explanation: For comparison, a standard, old-fashioned 12V module has 36 cells and has a MPP voltage around 17V. The 17V is needed to raise a 12V battery to 15.5V for equalizing in the summer, when the modules are hot and operating at reduced voltage. Extending this logic, a 48V battery needs 144-cell modules, in order to maintain a 68V MPP, in order to charge your 48V battery bank to 62V. Sanyos have 96 cells, not 144, and have a stated MPP of 55.8V. This is too low to charge your batteries fully. Will it work? Well, yes, in a fashion. As long as the array voltage is above the battery voltage, power will flow into them. Your batteries will always get charged when they're low. However, you will have a hard time getting them full. Fortunately, Sanyos are high-efficiency, with a slightly higher-than-usual MPP voltage, and Chama is about the coldest part of New Mexico. In winter, when the array is cold, the voltage is pushed up and you'll likely get them full - provided the day is long enough. It will help if your batteries are kept warm, thus needing lower voltage to fill. In summer, I predict that the only way to get your batteries full is with your generator. What's the cost of continuing as you are now? Reduced battery capacity and life over time. What's the solution? Wait for Midnite to come out with their Classic charge controller, which is promised to be able to handle 200 or 250 V maximum array voltage. It should be available any day now...(and has been that way for a year). Then rewire your modules into four pairs, and replace your PV input breakers with ones rated for higher voltage. Don't do that now, as the MX60 can't handle it: you will exceed the 150V input limit on cold sunny winter mornings,and it's not warranted if it fails. Please forgive me for the bad news. I thought you should know." Allan Sindelar -----Original Message----- From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Drake Chamberlin Allan and Brian Thanks for the answer to the problem. I think the Xantrex PWM chargers are going to be the most appropriate for these modules. The old Arco modules are incredibly long lasting. I hope the ones we are putting in today will last as long. Drake At 01:40 PM 3/20/2009, you wrote: >Drake, > >Just to add to Allan's excellent post, most of the Arco's made >before about 1985 had less than 36 cells. Some were 35-cell, most >were 33-cell, but there were also 32 and 30-cell units. > >You might want to look into rewiring the modules in higher voltage >series strings to get more "oomph" out of the MPPT controller, and >reduce transmission losses. However, be aware that many of those old >Arco modules had a sticker on them that said something like "do not >operate above 50VDC" > >I still have 12 Arco, 33-cell, model 16-2000 modules (16Vmp/2A) on >my off-grid house, wired in pairs for 24V and going through an >ancient Trace C-30A relay controller (not even PWM!). I've >contemplated wiring them for 36V and using MPPT, and I may someday, >but they have been working so well as is that I haven't bothered. >Even on hot days I often see 27.5V and 11-12A charging my 24V >battery bank, which I think is damn good performance from a set of >27-year-old modules. > >Brian Teitelbaum >AEE Solar _______________________________________________ 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
