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HI All,
First post to SolarPanelTalk. A little background on my situation. I have a small off-grid solar setup for a cabin in the mountains. I currently have 5 x 55w (12v) Arco panels connected to a BlueSky SB3000 (older model) MPPT charge controller. Batteries are 4 x 6v lead acid golf cart size batteries (no brand, explained below). Batteries are wired for 12v, so 2 in series connected in parallel to the other 2 in series. I went with 12v because I use several 12v devices and my inverter is 12v only and small (600w). Additionally with 5 panels, I can't wire them for 24v unless I only use 4 of the 5 panels- thus losing that extra 55w of power. So I'm stuck with the series/parallel battery bank configuration to get 12v. Now, some of you may be asking who/what is Arco solar panels? These panels were purchased back in 1986 along with the 4 batteries I'm using. The batteries were dry when purchased and sat for 20+ years without acid. In 2011 I finally bought battery acid and filled them up and setup the panels for the first time on a temporary mobile rack.
Since the location of this setup is remote, I'm unable to check on or use this system for 4-6 months of the year. For the first 3 winters I left 2 solar panels (~100w total) connected, sitting in a south window to keep a charge on the batteries over winter. Also, there are no loads connected over the winter, so discharging is minimal. This setup was working well and batteries were keeping a good charge for the following years. At the end of 2015, I mounted the 5 panels more permanently on the exterior of the cabin (east facing). Additionally I connected a 'Battery Life Saver' desulfator in 2015 and it has been connected continuously since then. The batteries did ok over the winter and were keeping a good voltage through the fall of 2016 (last year). However over last winter the fluid level in the batteries did drop down to just below the top of the lead plates in a couple of the batteries. I topped up with water last spring and system voltages were noticibly lower than previous years but only a couple of 10ths of a volt. Overall they still seemed in good condition last year.
This year when I went to the cabin for the first time I noticed the charging voltage was lower than expected for full sun. I was getting around 13.3v full sun (expecting 13.95v). 'Resting' voltage after charging was only about 12.5v where as it was up near 12.9-12.8v in years before. I checked the electrolyte level and there weren't any cells with fluid below the top of the plates. Topped them up with some distilled water and not much change in the charging voltage. I then checked voltage of each battery to see if there was a shorted cell in one of the batteries. What I found was two batteries in one of the series string were both ~6.3 to 6.4v. In the other series string one was 5.9v and the other was ~6.2v. Voltages were checked without charge input (I have to disconnect the battery bank from controller to access them). I did purchase a specific gravity tester from Napa but forgot to bring it with me on my first trip, but plan to check that when I return. Im wondering the the parallel configuration of the battery bank is creating this issue and causing two of the four batteries to take more load or have more charging resistance. I tried my best to keep resistances equal when I built the battery bank by connecting inverter/charge controller to mirrored points on the batteries so current is always flowing through the same length of jumper wires between batteries.
I'd like to get a few more years out of these batteries, so I'm wondering what would help to get the most life out of them. I get the feeling if I keep doing what I'm doing they won't make it through next winter. My first thought is to re-configure the order of the batteries in each series string- moving one battery from each string to the other. My other thought is to dump out the acid and put in some new acid which would be cheaper than buying new batteries for the next few years. I realize they won't last forever, but I'd rather save more money now for more appropriate batteries down the road. I'malso wondering if having so much charging without use for 4-6 months is also a problem. I'm giving though to some sort of automated load to give the batteries 'exercise' over the winter but don't have any solid plans yet.
Any thoughts appreciated.
a-
First post to SolarPanelTalk. A little background on my situation. I have a small off-grid solar setup for a cabin in the mountains. I currently have 5 x 55w (12v) Arco panels connected to a BlueSky SB3000 (older model) MPPT charge controller. Batteries are 4 x 6v lead acid golf cart size batteries (no brand, explained below). Batteries are wired for 12v, so 2 in series connected in parallel to the other 2 in series. I went with 12v because I use several 12v devices and my inverter is 12v only and small (600w). Additionally with 5 panels, I can't wire them for 24v unless I only use 4 of the 5 panels- thus losing that extra 55w of power. So I'm stuck with the series/parallel battery bank configuration to get 12v. Now, some of you may be asking who/what is Arco solar panels? These panels were purchased back in 1986 along with the 4 batteries I'm using. The batteries were dry when purchased and sat for 20+ years without acid. In 2011 I finally bought battery acid and filled them up and setup the panels for the first time on a temporary mobile rack.
Since the location of this setup is remote, I'm unable to check on or use this system for 4-6 months of the year. For the first 3 winters I left 2 solar panels (~100w total) connected, sitting in a south window to keep a charge on the batteries over winter. Also, there are no loads connected over the winter, so discharging is minimal. This setup was working well and batteries were keeping a good charge for the following years. At the end of 2015, I mounted the 5 panels more permanently on the exterior of the cabin (east facing). Additionally I connected a 'Battery Life Saver' desulfator in 2015 and it has been connected continuously since then. The batteries did ok over the winter and were keeping a good voltage through the fall of 2016 (last year). However over last winter the fluid level in the batteries did drop down to just below the top of the lead plates in a couple of the batteries. I topped up with water last spring and system voltages were noticibly lower than previous years but only a couple of 10ths of a volt. Overall they still seemed in good condition last year.
This year when I went to the cabin for the first time I noticed the charging voltage was lower than expected for full sun. I was getting around 13.3v full sun (expecting 13.95v). 'Resting' voltage after charging was only about 12.5v where as it was up near 12.9-12.8v in years before. I checked the electrolyte level and there weren't any cells with fluid below the top of the plates. Topped them up with some distilled water and not much change in the charging voltage. I then checked voltage of each battery to see if there was a shorted cell in one of the batteries. What I found was two batteries in one of the series string were both ~6.3 to 6.4v. In the other series string one was 5.9v and the other was ~6.2v. Voltages were checked without charge input (I have to disconnect the battery bank from controller to access them). I did purchase a specific gravity tester from Napa but forgot to bring it with me on my first trip, but plan to check that when I return. Im wondering the the parallel configuration of the battery bank is creating this issue and causing two of the four batteries to take more load or have more charging resistance. I tried my best to keep resistances equal when I built the battery bank by connecting inverter/charge controller to mirrored points on the batteries so current is always flowing through the same length of jumper wires between batteries.
I'd like to get a few more years out of these batteries, so I'm wondering what would help to get the most life out of them. I get the feeling if I keep doing what I'm doing they won't make it through next winter. My first thought is to re-configure the order of the batteries in each series string- moving one battery from each string to the other. My other thought is to dump out the acid and put in some new acid which would be cheaper than buying new batteries for the next few years. I realize they won't last forever, but I'd rather save more money now for more appropriate batteries down the road. I'malso wondering if having so much charging without use for 4-6 months is also a problem. I'm giving though to some sort of automated load to give the batteries 'exercise' over the winter but don't have any solid plans yet.
Any thoughts appreciated.
a-
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