Truth is there is likely more than enough capacity in the LFP battery the customer has but the manufacturer built a limit into the “box". The limit of our battery is set to 10C for 30 seconds. WAY more than any inverter can draw with even a small bank.
Larry On Sep 18, 2014, at 12:26 PM, b...@midnitesolar.com wrote: Yes, well of course there are these details. If the LFP surge is a limitation, but not its amount of overall energy storage, then you may have to add a very large amount of LFP storage to overcome that which could be overkill and cost a lot of extra $. It's all a compromise. boB On 9/18/2014 10:55 AM, Starlight Solar Power Systems wrote: > 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 >> >>
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