<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 class="Asgive ng" style="border-style:none;background:none">have to</span> set the AGS start voltage pretty high on sites where <span class="Asgive ng" 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 class="Asgive ng" style="border-style:none;background:none">use the full capacity of the battery </span>because <span class="Asgive ng" 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" 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 Sun, Apr 12, 2026 at 5:21 PM Zeke Yewdall 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"><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><div><br></div><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><div><br></div><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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