The only way to really prevent that is to disconnect everything but the solar array. Unfortunately, more than once we have seen customers disconnect the array but leave other phantom loads on.
When most inverters shut down on LV they are still drawing a few watts. And even with solar connected, if the voltage drops too low, the charge controller often will not start back up until reset. I suspect that could have happened in your case. .................................................................................................. Northern Arizona Wind & Sun - Electricity From The Sun Since 1979 Solar Discussion Forum: http://www.wind-sun.com/ForumVB/ .................................................................................................. ----- Original Message ----- From: Solar Plexus To: re-wrenches@lists.re-wrenches.org Sent: Sunday, December 20, 2009 4:22 PM Subject: [RE-wrenches] low voltage disconnect Wrenches. I have a customer with a stand-alone system with an XW inverter, XW controller, pole mounted array of four 235-watt panels, and 4 of the 8D gel batteries. He uses the system mostly on weekends. Winter came, the solar array was still set at about 30°, a snowstorm covered the panels while no one was there, and 4 days later the battery voltage was 6. The week-end use had been substantial, so I assume the batteries were low prior to the snowstorm. With no solar coming in, and loads still on, the battery voltage presumably went to Low Battery Cut Out voltage of 44 before the inverter disconnected the AC loads. With the AC loads disconnected, and no DC loads in the system, what caused the battery voltage to go to 6? I assume the XW controller used 2.5 watts continuous or 60 watt-hrs per day as battery voltage went from 44 volts to 10 volts when the controller would have shut off completely. What happens with the inverter when the battery goes below 44 volts? Does the inverter shut off and there is no more draw on the batteries, or does the inverter continue to draw the no-load draw of 28 watts, or does the inverter draw the search-load draw of 8 watts? At what voltage does the inverter stop drawing power? At 44 volts, the battery is presumed to be pretty dead. How many amp-hours are available in a 100 amp-hour 48v battery (4 12-v batteries in series) while drawing the voltage from 44 volts and 6 volts? Is there anything there or will the voltage just drop from 44 to 6 with very little power draw? The Low Voltage Disconnect is set for 44 volts, but if the inverter itself does not shut off, then the practical low voltage becomes the voltage the inverter stops working at. To protect the batteries, is there any advantage to limiting the low voltage to 44 volts as opposed to 6 volts. If so, is there some way to have the inverter shut itself off at low voltage? We have had this same thing happen with an Outback inverter, again taking the batteries to near zero. Is there any way that either the Outback or Sunny Island would operate differently than described above? Looking forward to any comments on these issues. Thank you. Lee Tavenner Solar Plexus ------------------------------------------------------------------------------ _______________________________________________ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Options & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules & etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
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