<html><head><meta http-equiv="Content-Type" content="text/html charset=windows-1252"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;">boB,<div><br></div><div>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.</div><div><br></div><div>Larry</div><div>
<br><div><div>On Sep 18, 2014, at 11:09 AM, <a href="mailto:boB@midnitesolar.com">boB@midnitesolar.com</a> wrote:</div><br class="Apple-interchange-newline"><div>
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One thing that could possibly be done is to have a smaller lead
acid battery in parallel with the LiFePo bank<br>
so the LiFePo contains most of the "energy" storage, but the LA
can supply the surges and low impedance<br>
source voltage.<br>
<br>
boB<br>
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On 9/18/2014 8:53 AM, Starlight Solar Power Systems wrote:<br>
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William,
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<div>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. </div>
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<div>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.</div>
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</div>
<div>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.</div>
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<div>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.</div>
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</div>
<div>Larry Crutcher</div>
<div><br>
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<div>
<div>On Sep 17, 2014, at 10:15 PM, William Miller <<a moz-do-not-send="true" href="mailto:william@millersolar.com">william@millersolar.com</a>>
wrote:</div>
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<div class="WordSection1"><p class="MsoNormal"><span style="font-family:"Arial","sans-serif";color:#1F497D">Larry:<o:p></o:p></span></p><div><span style="font-family:"Arial","sans-serif";color:#1F497D"> </span><br class="webkit-block-placeholder"></div><p class="MsoNormal"><font face="Arial, sans-serif"><font color="#1f497d">…</font><font color="#1f497d" size="3">...</font></font><span style="color:
rgb(31, 73, 125); font-family: Arial, sans-serif;
font-size: 12pt;">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.</span></p><div><span style="font-family:"Arial","sans-serif";color:#1F497D"> </span><br class="webkit-block-placeholder"></div><p class="MsoNormal"><span style="font-family:"Arial","sans-serif";color:#1F497D">William<o:p></o:p></span></p><div><span style="font-family:"Arial","sans-serif";color:#1F497D"> </span><br class="webkit-block-placeholder"></div><div><span style="font-family:"Arial","sans-serif";color:#1F497D"> </span><br class="webkit-block-placeholder"></div>
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