<div dir="ltr"><div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif">Could <span class="Asgive ng" style="border-style:none;background:none">it be that</span> the EV <span class="Asgive ng" style="border-style:none;background:none">SOC is somewhat faked by the manufacturers</span> because they know the mass market will not stand for "SOC drift" as an excuse?</div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif"><br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif">My wife had a Saab in the 2000s that would <span class="Asgive ng" style="border-style:none;background:none">go to</span> "0 miles remaining" but still keep running for over 50 miles. Ask me how I know. :)</div><br clear="all"></div><div><div dir="ltr" class="gmail_signature" data-smartmail="gmail_signature"><div dir="ltr"><br>Jason Szumlanski<div><span style="color:rgb(51,51,51);font-family:Roboto,RobotoDraft,Helvetica,Arial,sans-serif;font-size:13px">Principal Solar Designer | Florida Solar Design Group</span><br style="color:rgb(51,51,51);font-family:Roboto,RobotoDraft,Helvetica,Arial,sans-serif;font-size:13px"><span style="color:rgb(51,51,51);font-family:Roboto,RobotoDraft,Helvetica,Arial,sans-serif;font-size:13px">NABCEP Certified Solar Professional (PVIP)</span><br style="color:rgb(51,51,51);font-family:Roboto,RobotoDraft,Helvetica,Arial,sans-serif;font-size:13px"><span style="color:rgb(51,51,51);font-family:Roboto,RobotoDraft,Helvetica,Arial,sans-serif;font-size:13px">Florida State Certified Solar Contractor CVC56956</span></div><div><font color="#333333" face="Roboto, RobotoDraft, Helvetica, Arial, sans-serif">Florida Certified Electrical Contractor EC13013208</font></div><div><font color="#333333" face="Roboto, RobotoDraft, Helvetica, Arial, sans-serif"> </font></div><div><font color="#333333" face="Roboto, RobotoDraft, Helvetica, Arial, sans-serif"><br></font></div></div></div></div><br></div><br><div class="gmail_quote gmail_quote_container"><div dir="ltr" class="gmail_attr">On Mon, Apr 13, 2026 at 12:36 AM Bill Battagin via RE-wrenches <<a href="mailto:re-wrenches@lists.re-wrenches.org">re-wrenches@lists.re-wrenches.org</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><u></u>
<div>
<p>Seems kinda funny that the EV manus can pretty well nail the SOC
of their battery packs for reliable readout of range left and
percent of charge (SOC). We've been driving EVs (3 varieties) for
8 years now and this has been our experience. This now being done
with LiFePO4 batteries in EVs and it's not very often that an EV
battery get charged up to 100%. </p>
<p> Unless I'm missing something it seems our
industry-wide SOC monitoring is not as sophisticated, until it is
we're using voltage, with its limitations, for AGS. Is it just a
matter of having the best <span>coulomb</span> counter?...uh oh, now
I'm drifting out of my field.</p>
<p> I would love to see more webinars from our
manufacturers that get more into the weeds about the guts about
how LiFePO4 batteries with their BMS's interact with our systems
especially off-grid, our main market.</p>
<p>Bill</p>
<pre cols="72">Feather River Solar Electric
Bill Battagin, owner
4291 Nelson St. (Shipping)
5575 Genesee Rd. (USPS, UPS)
Taylorsville, CA 95983
530-284-7849, 258-1641(cell)
CA. C10 Lic # 874049
Solar Powered since 1982
Home of the Sunny Side Up
</pre>
<div>On 4/12/2026 3:14 PM, Jason Szumlanski
wrote:<br>
</div>
<blockquote type="cite">
<div dir="ltr">
<div>
<div class="gmail_default" style="font-family:arial,helvetica,sans-serif">Yep, totally
agree. However, <span style="border-style:none;background:none">then you start
facing</span> the issue of SOC drift if you can't get them
up to 100% regularly. </div>
<div class="gmail_default" style="font-family:arial,helvetica,sans-serif"><br>
</div>
<div class="gmail_default" style="font-family:arial,helvetica,sans-serif">Damned if you
do, damned if you don't. </div>
<div class="gmail_default" style="font-family:arial,helvetica,sans-serif"><br>
</div>
<div class="gmail_default" style="font-family:arial,helvetica,sans-serif">Right-sizing
all components is hard while staying within reasonable
budgets. I guess that's why we get paid the big bucks.</div>
<br clear="all">
</div>
<div>
<div dir="ltr" class="gmail_signature">
<div dir="ltr"><br>
Jason Szumlanski
<div><span style="color:rgb(51,51,51);font-family:Roboto,RobotoDraft,Helvetica,Arial,sans-serif;font-size:13px">Principal
Solar Designer | Florida Solar Design Group</span><br style="color:rgb(51,51,51);font-family:Roboto,RobotoDraft,Helvetica,Arial,sans-serif;font-size:13px">
<span style="color:rgb(51,51,51);font-family:Roboto,RobotoDraft,Helvetica,Arial,sans-serif;font-size:13px">NABCEP
Certified Solar Professional (PVIP)</span><br style="color:rgb(51,51,51);font-family:Roboto,RobotoDraft,Helvetica,Arial,sans-serif;font-size:13px">
<span style="color:rgb(51,51,51);font-family:Roboto,RobotoDraft,Helvetica,Arial,sans-serif;font-size:13px">Florida
State Certified Solar Contractor CVC56956</span></div>
<div><font color="#333333" face="Roboto, RobotoDraft, Helvetica, Arial, sans-serif">Florida
Certified Electrical Contractor EC13013208</font></div>
<div><font color="#333333" face="Roboto, RobotoDraft, Helvetica, Arial, sans-serif"> </font></div>
<div><font color="#333333" face="Roboto, RobotoDraft, Helvetica, Arial, sans-serif"><br>
</font></div>
</div>
</div>
</div>
<br>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Sun, Apr 12, 2026 at
6:03 PM Bill P. Battagin via RE-wrenches <<a href="mailto:re-wrenches@lists.re-wrenches.org" target="_blank">re-wrenches@lists.re-wrenches.org</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div>
<div style="font-family:arial,helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)">
<div>Jason,</div>
<div><br>
</div>
<div> I couldn't agree with you more about
over-sizing the battery when Off-grid and open loop. In
my opinion this is THE solution. Yes there's the extra
cost of the greater capacity battery however it solves
the generator angst issue (both customer and
installer). There is the added upfront cost of the
battery, maybe 30-35%? but over time much of that cost
will be recovered from lower genny fuel consumption,
repairs and maintenance, plus i'm guessing the L-ion
pack will last longer if its not worked as hard and
discharged as deeply. Obviously its a plus to also have
the benefit of more power autonomy it the sun ain't
shining.</div>
<div><br>
</div>
<div> Overall in the long run, maybe it does
come out a little more expensive, but its a better more
reliable system with less problems. We're more worried
about the gas in the generator going bad due to lack of
use than BMS shutdown. Is bad gas angst a thing?</div>
<div><br>
</div>
<div> Taylorsville Bill's $.02 worth,</div>
<div><br>
</div>
<div>
<pre><strong><span style="font-family:"courier new";color:black">Feather River Solar Electric</span></strong><span style="color:black"></span></pre>
<pre><strong><span style="font-family:"courier new";color:black">Bill Battagin, owner</span></strong><span style="color:black"></span></pre>
<pre><strong><span style="font-family:"courier new";color:black">4291 Nelson St. (Freight)</span></strong><span style="color:black"></span></pre>
<pre><strong><span style="font-family:"courier new";color:black">5575 Genesee Rd. (USPS, UPS)</span></strong><span style="color:black"></span></pre>
<pre><strong><span style="font-family:"courier new";color:black">Taylorsville, CA 95983</span></strong><span style="color:black"></span></pre>
<pre><strong><span style="font-family:"courier new";color:black">530-284-7849, 258-1641(cell)</span></strong><span style="color:black"></span><strong><span style="font-family:"courier new";color:black">CA.
C10 Lic # 874049
</span></strong><span style="color:black"></span><strong><span style="font-family:"courier new";color:black">Solar Powered since 1982</span></strong></pre>
</div>
<div><br>
</div>
<hr id="m_-7272947035172703228m_1963922959814541311zwchr">
<div><b>From: </b>"Jason Szumlanski via RE-wrenches" <<a href="mailto:re-wrenches@lists.re-wrenches.org" target="_blank">re-wrenches@lists.re-wrenches.org</a>><br>
<b>To: </b>"RE-wrenches" <<a href="mailto:re-wrenches@lists.re-wrenches.org" target="_blank">re-wrenches@lists.re-wrenches.org</a>><br>
<b>Cc: </b>"Jason Szumlanski" <<a href="mailto:jason@floridasolardesigngroup.com" target="_blank">jason@floridasolardesigngroup.com</a>>,
"Zeke Yewdall" <<a href="mailto:zeke@darkforestsolar.com" target="_blank">zeke@darkforestsolar.com</a>><br>
<b>Sent: </b>Sunday, April 12, 2026 2:28:40 PM<br>
<b>Subject: </b>Re: [RE-wrenches] AGS quiet time<br>
</div>
<div><br>
</div>
<div>
<div dir="ltr">
<div>
<div class="gmail_default" style="font-family:arial,helvetica,sans-serif">The
issue I have with open loop and LFP when off-grid
is that you <span style="border-style:none;background:none">have
to</span> set the AGS start voltage pretty high
on sites where <span style="border-style:none;background:none">there
is sometimes a large load</span> relative to
battery capacity. The voltage curve drops off too
fast around 20% to start the generator sometimes
before the BMS shuts down. You can't <span style="border-style:none;background:none">use
the full capacity of the battery </span>because
<span style="border-style:none;background:none">you're
faced with starting</span> the generator at
higher than necessary voltages. That takes away
one of the huge advantages of LFP over lead-acid:
more usable capacity.</div>
<br clear="all">
</div>
<div>
<div class="gmail_default" style="font-family:arial,helvetica,sans-serif">That
said, I have sites with huge batteries and low
loads that work great with open loop because the
batteries rarely approach deep discharge, and when
they do, there is enough time to "catch" the steep
part of the curve.</div>
<div class="gmail_default" style="font-family:arial,helvetica,sans-serif"><br>
</div>
<div class="gmail_default" style="font-family:arial,helvetica,sans-serif">In
a perfect world, everyone would play nice and
agree on communication standards, or at least just
let the dang inverter read the SOC and that's it. </div>
<br>
</div>
<div>
<div dir="ltr" class="gmail_signature">
<div dir="ltr"><br>
Jason Szumlanski
<div><span style="color:rgb(51,51,51);font-family:roboto,robotodraft,helvetica,arial,sans-serif;font-size:13px">Principal
Solar Designer | Florida Solar Design Group</span><br style="color:rgb(51,51,51);font-family:roboto,robotodraft,helvetica,arial,sans-serif;font-size:13px">
<span style="color:rgb(51,51,51);font-family:roboto,robotodraft,helvetica,arial,sans-serif;font-size:13px">NABCEP
Certified Solar Professional (PVIP)</span><br style="color:rgb(51,51,51);font-family:roboto,robotodraft,helvetica,arial,sans-serif;font-size:13px">
<span style="color:rgb(51,51,51);font-family:roboto,robotodraft,helvetica,arial,sans-serif;font-size:13px">Florida
State Certified Solar Contractor CVC56956</span></div>
<div><font color="#333333" face="Roboto, RobotoDraft, Helvetica, Arial, sans-serif">Florida
Certified Electrical Contractor EC13013208</font></div>
<div><font color="#333333" face="Roboto, RobotoDraft, Helvetica, Arial, sans-serif"> </font></div>
<div><font color="#333333" face="Roboto, RobotoDraft, Helvetica, Arial, sans-serif"><br>
</font></div>
</div>
</div>
</div>
<br>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Sun, Apr 12, 2026
at 5:21 PM Zeke Yewdall via RE-wrenches <<a href="mailto:re-wrenches@lists.re-wrenches.org" rel="nofollow noopener noreferrer" target="_blank">re-wrenches@lists.re-wrenches.org</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div dir="ltr">
<div>I used to be a firm believer in only
operating lithium batteries in open loop,
because trying to do closed loop with most
requipment was such a disaster of communications
tinkering at best. I would still try to operate
the AGS with SOC based controls as much as
possible, but still have a voltage catch in case
the SOC drifted off from reality. Outback would
let you have both at the same time. But still
no comms with the batteries.</div>
<br>
<div>But, if you can have the batteries and
inverter from the same manufacturer, which is
more and more possible, so you know closed loop
communications are going to work, that is much
nicer than trying to determine voltage based
start and stop points on a lithium battery. So
I'm coming around to using closed loop
communications since starting using matched
equipment.</div>
<br>
<div>I get not taking the SOC all the way to 100%
with the generator to leave some room for
solar. But I think it depends on your climate.
If you have some winter sun and can still get to
100% regularly, I think that can make sense.
But if you have no winter sun (like where I am
now -- typical PSH well under 1 for Dec and Jan
-- I've measured as low as 0.25PSH for the month
before -- then I am still a believer in getting
the batteries to 100% regularly (once every week
or two), even if that takes a generator.
Otherwise the SOC indicated by the BMS can drift
from reality. Some BMS's will recalibrate their
SOC if they get a voltage reading at rest at an
SOC lower than 100%, but many BMS's will only
recalibrate the SOC calculation when they reach
100% (same as ah counting SOC meters that have
to reach 100% to recalibrate/reset).</div>
</div>
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