Friends:
Here are the specific batteries I am looking at: http://www.oesoptimizedenergystorage.com/ William Gradient Cap_mini Lic 773985 millersolar.com <http://www.millersolar.com/> 805-438-5600 From: RE-wrenches [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of jarmo.venalai...@schneider-electric.com Sent: Monday, September 15, 2014 7:09 PM To: RE-wrenches Subject: Re: [RE-wrenches] LiFePo4 Hi: We've done some testing and operation of Lion battery banks in the 10 kWh range with our inverter chargers and so far the most important findings are: 1. The battery pack must have its own battery management system to: a. regulate the individual cell voltages during charge and discharge b. balance the cell voltages during charge and discharge c. adjust cell charging voltages due to temperature variations d. not provide a continuous float voltage to the battery bank d. provide a built in safety cutoff disconnect, which turns off the current if for any reason either the charge or discharge current is too high. A series string of Lion cells, without the battery management system functions above is very likely to result in damaged cells or worse. The most likely mechanism which ultimately causes damage is individual cell temperature or cell to cell voltage imbalance. 2. The inverter system must be designed so that the inverter never draws so much current that the current limit circuit in the battery bank is triggered. 3. It may be necessary to adjust the current limit circuit as they typically respond within milli-seconds and may be triggered on simple power up as the inverter cap bank charges up. 4. When working with Lion, the inverter/charger should be configured so that it is a simple current limited voltage source when in charge mode. The built in battery management system should take care of the required charge cycle operation. 5. Whether the pack is LiFePO4, Lion polymer or other does not appear to be as important as a having a reputable brand and more importantly a well designed built in battery management system. The short version is that lead acid cells are amazingly forgiving with regards charging and discharging voltages, currents and temperatures. Lion cells on the other hand are amazingly sensitive and going out of bounds on any of these can and will cause irreparable damage. Given the sensitivity, it doesn't make sense to take on responsibility for Lion battery management. Management of that sensitivity and responsibility is best left to the battery bank manufacturer. JARMO
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