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Oh, OK then. I thought that somebody had noticed a voltage drop
when surging.<br>
<br>
When people ask me if they can use LFP or other Lithium chemistry
batteries, I tell them yes because<br>
when they buy a LFP battery system, (or one of their Lithium Ion
relatives) it has all the protection<br>
and balancing built into it. It's simple to use with an off the
shelf charge controller.<br>
<br>
We were asked to add an input so that the LFP BMS could tell the
CC when to stop charging.<br>
That was a special case and I don't remember who's system that
was. Normally, I see what you just<br>
mentioned I think where it charges up to a voltage (Absorb) and
then immediately goes to Float<br>
which would be some very low voltage, enough to be called "off".
Couldn't be easier.<br>
<br>
Now we're just talking price compared to a tried and true LA
battery ?<br>
<br>
Some may remember Boeing's little problem recently though and that
may turn them off.<br>
<br>
boB<br>
<br>
<br>
<br>
On 9/18/2014 11:33 AM, Starlight Solar Power Systems wrote:<br>
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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.
<div><br>
</div>
<div>Larry<br>
<br>
<div>
<div>On Sep 18, 2014, at 12:26 PM, <a moz-do-not-send="true"
href="mailto:boB@midnitesolar.com">boB@midnitesolar.com</a>
wrote:</div>
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Yes, well of course there are these details.<br>
If the LFP surge is a limitation, but not its amount
of overall<br>
energy storage, then you may have to add a very large
amount of LFP storage to overcome that which<br>
could be overkill and cost a lot of extra $.<br>
<br>
It's all a compromise.<br>
<br>
boB<br>
<br>
<br>
On 9/18/2014 10:55 AM, Starlight Solar Power Systems
wrote:<br>
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cite="mid:13511563-8B62-4F9B-B9CB-3C305296AF37@starlightsolar.com"
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boB,
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<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
moz-do-not-send="true"
href="mailto:boB@midnitesolar.com">boB@midnitesolar.com</a>
wrote:</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>
<br>
<br>
<br>
On 9/18/2014 8:53 AM, Starlight Solar Power
Systems wrote:<br>
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William,
<div><br>
</div>
<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>
<div><br>
</div>
<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>
<div><br>
</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>
<div><br>
</div>
<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>
<div><br>
</div>
<div>Larry Crutcher</div>
<div><br>
<br>
<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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<p class="MsoNormal"><span
style="font-family:"Arial","sans-serif";color:#1F497D">Larry:<o:p></o:p></span></p>
<div><span
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<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>
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<p class="MsoNormal"><span
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