i have always used the good old e-meter/link 10. i manually program the charge efficiency at 99% (why won't the manufactures allow a 100% setting?). the problem is that 1% error... since the meter treats charge different than discharge.
the old e-meters seemed to handle this fine... but the newer ones (before they discontinued them) had a problem. with the shunt shorted (see time delay relay notes below), the meter read .4 amps of current flow, so obviously an accumulating error happens with these. i am about to replace one of these defective link 10's with a trace tm-500, which another local installer said works ok in this application (when manually set to 99% charge efficiency). i will report back to the list about the status of this "fix". but, even if it does work, as the grid reliability decreases in the coming years... when the grid is down, the meter will incorrectly report the battery soc, since it is obviously not at 99%. i had considered a rube-goldberg system where the meter would left programmed in the default setting to automatically calculate charge efficiency and a time delay relay would short out the shunt when the grid was up to keep the meter reading at 100%. if the tm-500 doesn't work, i will try this. either way, i will report back to the group as i know this is a vexing problem for many people who do gtwbb systems. as to the grid outage alarm, with the inverter out at the service disconnect, did you run a long, large gauge, twisted pair cable to the amp-hour meter in the house? do you have 2 extra conductors for an alarm? if not, how about an x-10 (or similar) remote switch at the grid disconnect to 'talk' to a light or alarm in the house? todd Incidentally, your comment about an amp-hour meter brings another question: a traditional amp-hour meter, like a TriMetric 2020,doesn't work well in GTWB situations, as the charged parameters are seldom met absent a grid outage, and thus the charge efficiency error can accumulate over time and lead to false readings. What do you use, Todd, or if you use a traditional amp-hour meter, how do you program it to fool it into maintaining accuracy in a system that always sits in float? Allan Allan Sindelar [mailto:[email protected]] [email protected] NABCEP Certified Photovoltaic Installer NABCEP Certified Technical Sales Professional New Mexico EE98J Journeyman Electrician Founder and Chief Technology Officer Positive Energy, Inc. 3209 Richards Lane (note new address) Santa Fe, New Mexico 87507 505 424-1112 [http://www.positiveenergysolar.com/] www.positiveenergysolar.com On 8/9/2012 10:02 AM, [mailto:[email protected]] [email protected] wrote: 99% of the grid-ties i do incorporate battery backup. when i am wiring a system into a house, i usually put the amp hour meter in the kitchen and only wire essential back up loads (water pump, communication, refrigeration & basic lighting) into the system. this design alerts the customer of when the grid is down and they need to go into 'conserve mode', and also eliminates power robbing waste. i am not sure why your customer would want to have the whole house backed up? i try to leave a couple of non essential, but noticeable circuits as 'grid only'. if the house is already wired and changing a circuit is not possible, you will need to somehow access a grid only circuit (the ac input to the inverter) and put some kind of alarm on it. hardware stores sell battery powered lights that come on when the power is off. one of these could be modified with a sonalert (or other audible alarm) which would come on to notify the customer to change their behavior. todd On Thursday, August 9, 2012 8:18am, "Allan Sindelar" [mailto:[email protected]] <[email protected]> said: Wrenches, For a grid-tied-with-backup system that is still in the design stage, we have a customer request for a signal to let them know when an outage occurs and they are running on backup power, so that they may turn off unnecessary loads and "go into backup consciousness". The problem is that the entire home would be on backup, with the GTWB system tied into a meter and main disconnect location away from the home, rather than the more typical main panel/subpanel approach at the home. Any relay-based alarm based on loss of grid AC would not likely trigger, as the switchover is too quick. Any ideas for simple solutions, please? Allan -- Allan Sindelar [mailto:[email protected]] [email protected] NABCEP Certified Photovoltaic Installer NABCEP Certified Technical Sales Professional New Mexico EE98J Journeyman Electrician Founder and Chief Technology Officer Positive Energy, Inc. 3209 Richards Lane (note new address) Santa Fe, New Mexico 87507 505 424-1112 [http://www.positiveenergysolar.com/] www.positiveenergysolar.com Sent from Finest Planet WebMail. Sent from Finest Planet WebMail. Sent from Finest Planet WebMail.
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