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--></style></head><body lang="EN-US" link="blue" vlink="purple"><div class="WordSection1"><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Verdana","sans-serif";color:#1f497d">Jay:</span></p><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Verdana","sans-serif";color:#1f497d"> </span></p><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Verdana","sans-serif";color:#1f497d">I am not sure how it would be possible for a grid-tied inverter to operate with any battery inverter if it was not connected to the battery inverter AC output. The grid-tied inverter needs to see correct voltage and frequency before it can start up. How else could this work?</span></p><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Verdana","sans-serif";color:#1f497d"> </span></p><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Verdana","sans-serif";color:#1f497d">I looked up all of the inverters you cited. In each case it may look to you like you are connecting to an input, it is really just reprogramming the inverter to turn the generator input into an extra output. All of the manufacturers provide warnings about doing this. Here is more information from each of the manufacturers:</span></p><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Verdana","sans-serif";color:#1f497d"> </span></p><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Verdana","sans-serif";color:#1f497d">Sol-arc: From the manual for the Sol-arc 15K-2P-N: You convert the Gen input to an output and make that your connection point. “<i>A full AC coupled solar system is not recommended as power control and monitoring is limited.”</i> </span></p><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Verdana","sans-serif";color:#1f497d"> </span></p><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Verdana","sans-serif";color:#1f497d">EG4: I could not find an “ev4” inverter anywhere online. There is an EG4 inverter. I read the manual and it looks like the EG4 works just like the Sol-arc: You program the generator input to actually be an output. The EG4 abruptly disconnects that output when battery SOC reaches a programmed level-- There is apparently no frequency shift function. The manual is pretty inadequate on this point but they do provide a <a href="https://www.youtube.com/watch?v=vRAq9g34VcI&ab_channel=EG4Electronics">video</a>.</span></p><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Verdana","sans-serif";color:#1f497d"> </span></p><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Verdana","sans-serif";color:#1f497d">Fortress: The same as above is true about using the generator input for AC-coupling on the Fortress FP-Envy-12k. From that manual<i>: It is forbidden to connect the Generator in Gen Port when AC Coupled. </i>That is because when AC-coupling, the generator input is no longer an input.</span></p><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Verdana","sans-serif";color:#1f497d"> </span></p><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Verdana","sans-serif";color:#1f497d">So while it appears one connects an AC-Coupled inverter to battery inverter inputs, it is just a reprogramming of the generator input to be an output. In all cases that I can see there is still no voltage control of AC-coupled battery charging.</span></p><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Verdana","sans-serif";color:#1f497d"> </span></p><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Verdana","sans-serif";color:#1f497d">I am aware that to try and provide some modicum of control over the battery charging from AC-coupled sources, a scheme was invented to shift the output frequency and taper or shut down AC-coupled power. This is a work-around, not a design. In each and every one of these systems it is pretty clear there is little control over battery charging voltage. These systems do not support three stage battery charging like a DC charge controller can.</span></p><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Verdana","sans-serif";color:#1f497d"> </span></p><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Verdana","sans-serif";color:#1f497d">When AC-coupled charging is connected to batteries with BMS in certain conditions battery voltage spikes can occur. See section 2.2 of this <a href="https://www.victronenergy.com/live/ac_coupling:start">article.</a></span></p><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Verdana","sans-serif";color:#1f497d"> </span></p><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Verdana","sans-serif";color:#1f497d">There are limited advantages to AC coupling:</span></p><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Verdana","sans-serif";color:#1f497d"> </span></p><p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l0 level1 lfo1"><span style="font-size:12.0pt;font-family:Symbol;color:#1f497d"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman""> </span></span></span><span style="font-size:12.0pt;font-family:"Verdana","sans-serif";color:#1f497d">AC coupling allows reduced wire gauge for long-haul feeders. This is no longer as necessary with new 600 volt input charge controllers.</span></p><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Verdana","sans-serif";color:#1f497d"> </span></p><p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l0 level1 lfo1"><span style="font-size:12.0pt;font-family:Symbol;color:#1f497d"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman""> </span></span></span><span style="font-size:12.0pt;font-family:"Verdana","sans-serif";color:#1f497d">AC Coupling allows an easier upgrade path for a customer that has grid-tied inverters and wants to add batteries. I am not sure most batteries can survive for long with the crude charging algorithm provided, so I would hesitate to recommend this.</span></p><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Verdana","sans-serif";color:#1f497d"> </span></p><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Verdana","sans-serif";color:#1f497d">In my opinion AC-coupled battery charging with even the newest inverters is a crude affair. I am not a fan.</span></p><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Verdana","sans-serif";color:#1f497d"> </span></p><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Verdana","sans-serif";color:#1f497d">William</span></p><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Verdana","sans-serif";color:#1f497d"> </span></p><div><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Arial","sans-serif";color:#1f497d">Miller Solar</span></p><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Arial","sans-serif";color:#1f497d">17395 Oak Road, Atascadero, CA 93422</span></p><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Arial","sans-serif";color:#1f497d">805-438-5600</span></p><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Arial","sans-serif";color:#1f497d"><a href="http://www.millersolar.com/"><span style="color:blue">www.millersolar.com</span></a></span></p><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Arial","sans-serif";color:#1f497d">CA Lic. 773985</span></p><p class="MsoNormal"><span style="color:#1f497d"> </span></p></div><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Verdana","sans-serif";color:#1f497d"> </span></p><div><div style="border:none;border-top:solid #b5c4df 1.0pt;padding:3.0pt 0in 0in 0in"><p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> Jay [mailto:<a href="mailto:jay.peltz@gmail.com">jay.peltz@gmail.com</a>] <br><b>Sent:</b> Saturday, October 28, 2023 1:58 PM<br><b>To:</b> <a href="mailto:william@millersolar.com">william@millersolar.com</a>; RE-wrenches<br><b>Subject:</b> Re: [RE-wrenches] AC Coupling</span></p></div></div><p class="MsoNormal"> </p><div><p class="MsoNormal">I’m going to both agree and disagree </p></div><div><p class="MsoNormal"> </p></div><div><p class="MsoNormal">Agree The older inverters ( Schneider, Outback, etc) your drawing is correct. </p></div><div><p class="MsoNormal"> </p></div><div><p class="MsoNormal">Disagree For many new inverters ( sol ark, ev4, fortress) they bring ac coupling into the inverter directly. </p></div><div><p class="MsoNormal">Usually on the generator input and not in the backup loads panel. </p></div><div><p class="MsoNormal"> </p></div><div><p class="MsoNormal">And I will also disagree about the statement that these inverters are not designed for ac coupling. </p></div><div><p class="MsoNormal">Agreed that the earlier non rule 21 compliant versions didn’t have any internal control and required external relay control to prevent overcharge. </p></div><div><p class="MsoNormal"> </p></div><div><p class="MsoNormal">Newer versions of Schneider, OB, have frequently shift which works with newer gt inverters to address the ac coupling overcharge concerns. While creating potential new issues for loads with up to 64 hz. </p></div><div><p class="MsoNormal"> </p></div><div><p class="MsoNormal"> </p></div><div><p class="MsoNormal">Jay</p></div><div><p class="MsoNormal"> </p></div><div><p class="MsoNormal"> </p></div><div><p class="MsoNormal"> </p></div><div><p class="MsoNormal"> </p></div><div><p class="MsoNormal"><br><br></p><p class="MsoNormal" style="margin-bottom:12.0pt">On Oct 28, 2023, at 2:15 PM, William Miller via RE-wrenches <<a href="mailto:re-wrenches@lists.re-wrenches.org">re-wrenches@lists.re-wrenches.org</a>> wrote:</p></div><blockquote style="margin-top:5.0pt;margin-bottom:5.0pt"><div><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Times New Roman","serif""></span></p><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Verdana","sans-serif"">Friends:</span></p><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Verdana","sans-serif""> </span></p><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Verdana","sans-serif"">I am starting to get the impression that there is a diversion on the understanding of the definition of AC coupling within the industry. I think this definition needs to be clarified.</span></p><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Verdana","sans-serif""> </span></p><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Verdana","sans-serif"">Below is a diagram of what I understand is a DC coupled system (I hope these diagrams come through):</span></p><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Verdana","sans-serif""> </span></p><div><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Verdana","sans-serif""><image003.png></span></p></div><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Verdana","sans-serif""> </span></p><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Verdana","sans-serif"">A battery inverter that receives AC power into an AC input port is <u>not</u> AC coupled.</span></p><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Verdana","sans-serif""> </span></p><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Verdana","sans-serif"">Here is an AC-coupled system:</span></p><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Verdana","sans-serif""> </span></p><div><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Verdana","sans-serif""><image005.png></span></p></div><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Verdana","sans-serif""> </span></p><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Verdana","sans-serif"">What makes AC-Coupled systems unique are the problems presented by sending power <u>backwards</u> through a battery inverter. This is not how battery inverters were originally designed to operate. These systems require careful consideration to avoid battery overcharging.</span></p><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Verdana","sans-serif""> </span></p><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Verdana","sans-serif"">Do we have consensus on this definition?</span></p><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Verdana","sans-serif""> </span></p><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Verdana","sans-serif"">William Miller</span></p><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Verdana","sans-serif""> </span></p><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Arial","sans-serif"">Miller Solar</span></p><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Arial","sans-serif"">17395 Oak Road, Atascadero, CA 93422</span></p><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Arial","sans-serif"">805-438-5600</span></p><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Arial","sans-serif""><a href="http://www.millersolar.com/">www.millersolar.com</a></span></p><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Arial","sans-serif"">CA Lic. 773985</span></p><p class="MsoNormal"> </p><p class="MsoNormal"> </p><p class="MsoNormal" style="margin-bottom:12.0pt"><span style="font-size:12.0pt;font-family:"Times New Roman","serif"">_______________________________________________<br>List sponsored by Redwood Alliance<br><br>Pay optional member dues here: <a href="http://re-wrenches.org">http://re-wrenches.org</a><br><br>List Address: <a href="mailto:RE-wrenches@lists.re-wrenches.org">RE-wrenches@lists.re-wrenches.org</a><br><br>Change listserver email address & settings:<br><a href="http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org">http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org</a><br><br>There are two list archives for searching. 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