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--></style></head><body lang="EN-US" link="blue" vlink="purple"><div class="WordSection1"><p class="MsoPlainText">Mark:</p><p class="MsoPlainText"> </p><p class="MsoPlainText">I do not think line voltage is an appropriate criteria for controlling an AC coupled system for these reasons:</p><p class="MsoPlainText" style="margin-left:.5in"><span style="mso-list:Ignore">1.<span style="font:7.0pt "Times New Roman""> </span></span>My understanding of how an AC coupled system works does not match yours. The concept is still black magic to me, but as I understand it, when you use GT inverters to charge batteries through a battery inverter, there is no charge control. This is the essence of this problem. The batteries will over-charge if you do not intervene. Remember, in an AC coupled system you are charging batteries by running power <u>into</u> the <u>output</u> of the battery inverter, or backwards to the normal power flow. I understand this is why the normal charge control system does not work.</p><p class="MsoPlainText" style="margin-left:.5in"><span style="mso-list:Ignore">2.<span style="font:7.0pt "Times New Roman""> </span></span>If the battery charging does not stop, there can be no cause and effect that will cause line voltage to rise.</p><p class="MsoPlainText" style="margin-left:.5in"><span style="mso-list:Ignore">3.<span style="font:7.0pt "Times New Roman""> </span></span>Even if 2 above were not true, batteries, as they approach full charge, taper their use of charging source, so you cannot expect any significant change in charge current when charging stops.</p><p class="MsoPlainText" style="margin-left:.5in"><span style="mso-list:Ignore">4.<span style="font:7.0pt "Times New Roman""> </span></span>There are too many other factors that can affect line voltage. If you set some circuit to do something when live voltage changes beyond a certain thresholds, this trigger will happen randomly as line voltage changes for external reasons.</p><p class="MsoPlainText"> </p><p class="MsoPlainText">I hate to break the news, but you need to find some way to communicate the battery voltage to the GT inverter output. You don\u2019t have to run the GT inverter AC output all the way to the battery inverter panel, but you will need to get a control signal connection between the two systems.</p><p class="MsoPlainText"> </p><p class="MsoPlainText">Caveat: I don\u2019t pretend to know thoroughly about how AC coupled systems work, but this is how I understand them. Maybe others can verify my conclusions.</p><p class="MsoPlainText"> </p><p class="MsoPlainText">William</p><p class="MsoPlainText"> </p><p class="MsoPlainText"> </p><p class="MsoPlainText">Miller Solar</p><p class="MsoPlainText">17395 Oak Road, Atascadero, CA 93422</p><p class="MsoPlainText">805-438-5600</p><p class="MsoPlainText"><a href="http://www.millersolar.com">www.millersolar.com</a></p><p class="MsoPlainText">CA Lic. 773985</p><p class="MsoPlainText"> </p><p class="MsoPlainText">-----Original Message-----<br>From: RE-wrenches [mailto:<a href="mailto:re-wrenches-bounces@lists.re-wrenches.org">re-wrenches-bounces@lists.re-wrenches.org</a>] On Behalf Of Mark Frye<br>Sent: Sunday, November 3, 2019 9:39 AM<br>To: <a href="mailto:re-wrenches@lists.re-wrenches.org">re-wrenches@lists.re-wrenches.org</a><br>Subject: Re: [RE-wrenches] Parts List For AC Couple Disconnect</p><p class="MsoPlainText"> </p><p class="MsoPlainText">Hi William,</p><p class="MsoPlainText"> </p><p class="MsoPlainText">Thanks, you bring up issues that are important to me here.</p><p class="MsoPlainText"> </p><p class="MsoPlainText">In particular, my situation is that the GT inverter is inter-tied a </p><p class="MsoPlainText">couple sub panels upstream of where I want to put the BB inverter. The </p><p class="MsoPlainText">distance is long, so I am looking for a solution where I don't have to </p><p class="MsoPlainText">run a cable between the two.</p><p class="MsoPlainText"> </p><p class="MsoPlainText">In general, I do wonder about using AC line voltage rise to take the Gt </p><p class="MsoPlainText">inverters off line. The main goal is to prevent excess voltage at the </p><p class="MsoPlainText">battery, so monitoring battery voltage is most direct, and there are </p><p class="MsoPlainText">simple solutions for that.</p><p class="MsoPlainText"> </p><p class="MsoPlainText">Is AC line voltage a suitable metric for achieving the same goal?</p><p class="MsoPlainText"> </p><p class="MsoPlainText">Here is where I could use Wrench knowledge to confirm my thinking, that </p><p class="MsoPlainText">being:</p><p class="MsoPlainText"> </p><p class="MsoPlainText">- With excess energy in the system, the charger moves it into the </p><p class="MsoPlainText">battery, raising it's voltage until it reaches it high charging voltage </p><p class="MsoPlainText">set point</p><p class="MsoPlainText"> </p><p class="MsoPlainText">- Once the battery reaches it's high voltage set point, the charger </p><p class="MsoPlainText">stops putting energy into the battery</p><p class="MsoPlainText"> </p><p class="MsoPlainText">- With no other place to put the excess energy, the AC voltage rises</p><p class="MsoPlainText"> </p><p class="MsoPlainText">Am I getting this right, the reason to disconnect AC coupled inverters </p><p class="MsoPlainText">when the battery if full is not to prevent the batteries from being </p><p class="MsoPlainText">overcharged, but rather to prevent the AC line from becoming unstable?</p><p class="MsoPlainText"> </p><p class="MsoPlainText">I am hoping this is correct and that with $200 of industrial grade </p><p class="MsoPlainText">devices from Digikey I can implement a robust control that will </p><p class="MsoPlainText">disconnect the GT inverters before the AC line goes so high that the BB </p><p class="MsoPlainText">inverter faults.</p><p class="MsoPlainText"> </p><p class="MsoPlainText">Mark</p><p class="MsoPlainText"> </p><p class="MsoPlainText"> </p><p class="MsoPlainText"> </p><p class="MsoPlainText">_______________________________________________</p><p class="MsoPlainText">List sponsored by Redwood Alliance</p><p class="MsoPlainText"> </p><p class="MsoPlainText">List Address: <a href="mailto:RE-wrenches@lists.re-wrenches.org">RE-wrenches@lists.re-wrenches.org</a></p><p class="MsoPlainText"> </p><p class="MsoPlainText">Change listserver email address & settings:</p><p class="MsoPlainText"><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></p><p class="MsoPlainText"> </p><p class="MsoPlainText">List-Archive: <a href="http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html">http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html</a></p><p class="MsoPlainText"> </p><p class="MsoPlainText">List rules & etiquette:</p><p class="MsoPlainText"><a href="http://www.re-wrenches.org/etiquette.htm">www.re-wrenches.org/etiquette.htm</a></p><p class="MsoPlainText"> </p><p class="MsoPlainText">Check out or update participant bios:</p><p class="MsoPlainText"><a href="http://www.members.re-wrenches.org">www.members.re-wrenches.org</a></p><p class="MsoPlainText"> </p></div></body></html>