Colleagues:
I believe that circulating currents in multi-string battery installations are a major cause of premature failure of such a system. I think it is important to monitor these currents. Most telling would be checking these currents in an at-rest scenario. It would be helpful to have a baseline at install and then check periodically. Measuring these currents with any type of DC clamp-on meter can be inaccurate at best. In a conversation with Steve Higgins at a recent trade show I came up with this idea that may have some merit: If an install has more than one string of batteries, install an appropriately sized shunt in the negative lead of each string. At any later date you can apply any decent voltmeter with a millivolt scale and check for battery string imbalance with some degree of accuracy. Shunts are cheap and readily available and if you avoid the brand that Outback uses in the Radian GSLC cabinets, they are relatively rugged. We will be trying this in any future install with multiple strings, although we avoid this if at all possible. William Miller [image: Gradient Cap_mini] Lic 773985 millersolar.com <http://www.millersolar.com/> 805-438-5600 *From:* RE-wrenches [mailto:[email protected]] *On Behalf Of *John Blittersdorf *Sent:* Wednesday, July 18, 2018 6:24 PM *To:* RE-wrenches *Subject:* Re: [RE-wrenches] Electrolyte Dilution vs Voltage Mac, I was about to ditto Ray with his more common than I would like scenario of battery death when I saw your mention of the 2nd string not connected. It is always nice to see a solution that is simple and should have been considered, but wasn't. The assumption with battery issues usually is that they are actually hooked up! I often thought that it would be worth the money to supply a cheap AC/DC clamp meter with every installation so that a phone consultation could quickly determine if the strings were unbalanced and what might be the reason. Bad cells and bad connection will usually show up in a current check and then a quick voltage check of each battery with a load on the system will show the culprit if a bad cell and corrosion present might find the bad connection. I use Interstate L16's most of the time and find that the life is typically 6 years. I used to call them a 7 to 10 year battery but kept racheting back the claim until I now call them a 5 to 7 year battery with more if properly maintained. I have seen 10 years but it is rare. John Blittersdorf
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