Mike, I approached it as if the batteries where installed in a UPS system. What constant float voltage would the batteries be charged at during grid-up, so they would be ready for grid-down?
I would use 53.2V for Float and for Sell. I also recommend to use software on the inverter to automatically bring the batteries to Absorb periodically. Most inverters have a setting to do this daily. The Absorb Time can be rather short since the Depth of the Discharge is so low. Of course, I would use different Absorb settings for an off-grid location. I am not sure what you mean by "wide open". The Charge Controller should go wide open so long as it can stay in Bulk mode while the inverter is selling. I have seen settings on the CC that cause it to go into Float and then the inverter has nothing to sell. I would not set the float to 55V for hours on end. The batteries might start to off-gas. At the same time, you can adjust Sell seasonally for inverters that do not Temperature Correct the Sell Voltage. Concorde's Lifeline AGM Technical Manual has a temperature chart that explains the V/T relationship. Good Luck, Maverick Maverick Brown BSEET, NABCEP Certified Solar PV Installer R # 091209-26 President & CEO Maverick Solar Enterprises, Inc. -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of [email protected] Sent: Thursday, April 07, 2011 8:31 AM To: RE-wrenches Subject: [RE-wrenches] Float, Sell Voltages Trying to tweak a couple of battery based grid-tie systems.Trying to maximize sell back without frying or draining the batteries. Have gotten various opinions from manufacturer's techs, so why not a few more...... Concord AGM's set now as follows: Bulk = 57.2v float = 53.2v sell = 52v It is my understanding that sell is actually a "low end float" on a grid-tie system and to keep the CC "wide open" for sellback, I might set the float to around 54.5v+ ( and maybe even as high as 55v?) and the sell voltage a bit higher - (53.2?) with the understanding that if grid goes down for extended period of time that the float must be set back to 53.2. Any thoughts? One other thing....with 4.3kW PV array, what would you expect as the maximum sell wattage to show up at peak sun? (my guess is 3.3 - 3.5) Holt E. Kelly Holtek Fireplace & Solar Products 500 Jewell Dr. Waco TX. 76712 254-751-9111 www.holteksolar.com _______________________________________________ List sponsored by Home Power magazine List Address: [email protected] 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 _______________________________________________ List sponsored by Home Power magazine List Address: [email protected] 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
