boB, When charging a LFP battery, the charge terminates when absorb voltage is reached unless you have an enormous charger in which case you will need to terminate based on AH returned. You would also need to isolate the LA battery to finish charging it. Plus, LA needs higher voltages than LFP. I don’t think would solve Williams problem. A better solution would be another LI-ion bank that is not current limited. Just a 50AH bank could provide an additional 500amps.
Larry On Sep 18, 2014, at 11:09 AM, b...@midnitesolar.com wrote: One thing that could possibly be done is to have a smaller lead acid battery in parallel with the LiFePo bank so the LiFePo contains most of the "energy" storage, but the LA can supply the surges and low impedance source voltage. boB On 9/18/2014 8:53 AM, Starlight Solar Power Systems wrote: > William, > > This is one reason I choose to avoid the "black box" approach to Li-ion > batteries for our customers. There are several companies offering enclosed > battery/controls like the OES. Their approach does not match well to the > off-grid and mobile markets that I serve. > > Since most LFP batteries can handle 10C for up to 30 seconds (Winston LFP can > surge to 20C!) and 2C-3C continuous discharge, it makes sense to me to design > a protection system that can't utilize that capability. Our LFMP battery has > an external CPU that I can program. We also use external high current relays > for the protective circuits so the full load of the inverter can be put to > use. > > With a LFP battery bank of 48 volts and 400AH, somewhat small for off grid, > the battery can operate continuously at 1200 amps or about 60kW output and > surge to 4000 amps/600kW. This obviously is way beyond the demand capability > of the inverter(s). A quick look at the SI6048 data sheet shows maximum AC > current is 11kW for 3 seconds. > > I am glad you noticed the extremely low voltage sag under load. This feature > means lower current which should translate to longer life for inverters. It > also means starting loads that you can’t with a similar sized lead acid > battery. A 1C load typically has only 0.2 volt sag. For 48 volt systems, this > means maintaining 51.2 volts throughout the full battery use. In fact, a 1C > load will still only have 0.2 volt drop until about 90% discharged. Simply > amazing. > > Larry Crutcher > > > On Sep 17, 2014, at 10:15 PM, William Miller <will...@millersolar.com> wrote: > > Larry: > > …...The internal battery management system will allow them to disconnect > under surge loads, just when you need your batteries to stay connected. I > will be conversing with the manufacturer to learn more about them. > > William > > > > > _______________________________________________ > List sponsored by Redwood Alliance > > List Address: RE-wrenches@lists.re-wrenches.org > > Change listserver email address & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > List-Archive: > http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html > > List rules & etiquette: > www.re-wrenches.org/etiquette.htm > > Check out or update participant bios: > www.members.re-wrenches.org > _______________________________________________ List sponsored by Redwood Alliance List Address: RE-wrenches@lists.re-wrenches.org Change listserver email address & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html List rules & etiquette: www.re-wrenches.org/etiquette.htm Check out or update participant bios: www.members.re-wrenches.org
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