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
<mailto: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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