Wow, this has been a wonderful and fruitful thread. First, Ron let me thank you for some impressive responses, and great information. I have some nits, but those are small and inconsequential, so I'll leave them to later. However, I want to chime in a bit just to set a frame of reference, if everyone will be patient with me. I'm concerned that one person's interpretation of "grey" will be misconstrued and quoted as gospel "gray" from now until eternity.
Specifically, Ron you answered Darryl that "Your recommendation to customers is 100% accurate… It is better to use low charge currents." I want to be clear, however, that your definition of "low" is extremely different that that of most solar designers. Darryl was suggesting "...never charge faster than C/10 and C/15 or C/20 is better" whereas you were saying "It is usually recommended to use a range of 10% to 13% of the battery’s 20-hour rate." I know that might not sound like much of a difference, but let's take a quick survey -- who among you wrenches normally install greater than 6kW of PV per 1,000 AH of battery at 48 volts? Whoa, not a lot of hands..... Do the math, but that's roughly what it takes to obtain a C/10 charge rate with straight PV. In all my years of working the wholesale trade, the systems I've seen which could theoretically achieve a C/10 charge rate are statistically insignificant. Systems which could perhaps achieve C/20 (except for those pesky oft-ignored daytime loads)...lot more hands in the air now. Systems which which hope and pray to someday hit C/100 (if the owners go off on vacation)....Bing Bing Bing -- you win the prize! Climbing off my soapbox, my point is that Ron, your definition as a battery manufacturer of "low" should be used with a clear reference to what "high" would be. Just want to clarify that before we all start hearing "but Trojan says I should charge at low current levels, so my 500W PV array will be just fine for that 1,000 AH battery!!!" The one question I have about the new Trojan 2V L16s would be what, exactly, is the benefit they provide for the designer and installer? When I look at the design, it looks like it's just using an existing case with three 350AH cells connected in parallel (2V) inside, rather than the standard series connection (6V) or better yet using a single 1,100AH cell. If good design practice calls for no more than three strings (cells) in parallel, then good practice would call for no more than a single string of these specific batteries, since any more than that would mean 6, 9 or more cells in parallel. Count the caps, folks. How about those watering chores. Measuring specific gravities? Shoot me first, please! I think Blair was right about looking at true industrial cells. So on to the nit -- can you send me a copy of the Excel file of the IEC 61427 graph? Gmail doesn't show the Excel graph, and the .png file shows up as little more than a thumbnail -- I can grok the essential info from the other graphs and tables, but that 13 years worth of data just doesn't come through in a legible manner, least not to my aging eyes. This discussion is much appreciated Phil Undercuffler On Thu, Jul 15, 2010 at 5:57 PM, Ronald Paredes <rpare...@trojanbattery.com>wrote: > Hello Ray, > > > > Glad to be helpful… > > > > The basic scope of the IEC 61427standard is to provide general information > relating to the requirements of batteries in RE applications, and more > importantly, the test methods that will test the battery’s ability to do > well in RE applications. The standard covers several tests. The most > relevant tests are: > > > > · Capacity test > > · Suitability for floating operation > > · Cycle endurance test at partial state of charge (deficit > charging) > > · Endurance test in overcharge > > · Charge retention test > > Most of the tests are very typical for battery characterization. The most > important test is the cycle endurance test at partial state of charge > because it tests battery’s ability to do well even when the battery doesn’t > get a full charge, which happens all too often in RE applications. This is > also a high temperature test, so it tests the battery’s ability to do well > in extreme temperatures. The battery fails the test if the capacity falls > below 80% or its rated capacity, or if the voltage falls below a certain > threshold. Below is a graph of what the test looks like. > > > > > > Each block represents a year. This test ran about 13 years… > > > > Please let me know if this provides enough information/background, or if > you have any other questions. > > > > Thanks for your reply. > > > > > > Best Regards, > > > > Ronald Paredes > > Technical Product Manager – Renewable Energy > > *Trojan Battery Company* > > > > 12380 Clark Street > > Santa Fe Springs, CA 90670 > > Tel: (562)236-3000 Ext. 3066 > > Fax: (562)236-3279 > > rpare...@trojanbattery.com > > www.trojanbattery.com > > > > *Trojan Battery Company - Clean Energy for Life™* > > >
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