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Forum Index : Solar : multiple battery strings how to ?
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| ashenash Newbie  Joined: 02/11/2012 Location: United StatesPosts: 3 |
Hi to everyone on this great forum. I have a working system installed, but would like to add batts Please tell me if I can/should safely add 4 more 6 volt batteries to my system. I now have: 4-24v panels feeding (2 panels per mppt controller) 2-15 amp mppt controlers feeding a 12v-450ah (4-6 volt series/parallel) battery bank feeding a 12v 5k inverter feeding houshold loads My goal is to keep my 12v inverter but add more more battery capacity but I understand the limitations I would like to add 4 more 6v batts series/parallel When I searched this question I found this... Battery banks with multiple strings are more likely to develop cells with unequal states of charge. Weak cells will be difficult to detect because they will “steal” from the surrounding cells. The system will suffer as a whole and will cost you more in the long run. Dankoff, Windy. "Batteries: How to keep Them Alive for Years & Years...." Home Power Magazine #69. Feb. - Mar. 1999. 46-47. I fully understand this concept. Too many strings cause imbalance in indidvidual batts. It seems evident that I can add multiple strings (6v batts connected in series to create 12v string to be paralleled to the exsisting bank) since I will use 2 controllers feeding opposite ends of the battery bank. Comments please Thanks Bert |
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| VK4AYQ Guru  Joined: 02/12/2009 Location: AustraliaPosts: 2539 |
Hi Bert The series parallel system you propose will work OK but there is some issues with battery matching when adding new batteries to older ones, and if different model or style, such as Gell cell of SLA or flooded lead acid, if you can stick to the same model and type, all should work. It is a good Idea to be able to isolate each string for testing and equalising charging if nessasary. Do you regulators have provision for a 16 volt equalisation charge? If not you may need to put a bypass switch in the charging and manually monitor equalisation charging. While the quote is correct we live in a world of compromise so have to make do the best we can. So isolate and check individual batteries as part of your maintainence schedule. All the best Bob Foolin Around |
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| ashenash Newbie Joined: 02/11/2012 Location: United StatesPosts: 3 |
Thanks Bob for the reply, Thats what I thought, just wanted to check with some folks with more experience than I. Couple more Comments and Questions. Yes. I'm using all matched batts. GC2 6 volt golf cart. My oldest are 6 months old with maybe 50 cycles. Will they be extremely mismatched with new batts ? How much of an imbalance is too much ? No I have no way to go to 16v for EQ. My morningstar mppt 15 units equalize at 14.9v . Is this enough ? I currently have no way to isolate besides disconnecting cables. Would you recommend a blade type cutoff or those cable ends with a rotary cutoff built in ? Or is there something better for high amps ? I'm trying to avoid more fuses. Thanks in advance Bert |
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| VK4AYQ Guru Joined: 02/12/2009 Location: AustraliaPosts: 2539 |
Hi Bert Shouldn't be any significant difference in a six month old battery, you can check by fully charging each battery and let sit overnight and measure voltages for differences between batteries, also by setting up batteries negative connected and then use a milliamp meter across the positive terminals a current flow will indicate a miss match, in saying that there will always be slight differences so a small current is acceptable if you leave the meter connected for several hours and the current has not decreased there is a problem with one battery. By using this method it is possible to match batteries and minimise losses due to mismatch. In practice if the batteries are good condition they will equalise with a good charge, you may need to put a regulator bypass switch to get the full voltage of the panels for equalisation.Your 14.9 volts is close to the mark and OK if all cells are matched. The higher voltage is a measure I use to try to equalise miss matched cells. It is hard to get a good blade switch now all Chinese junk, it is netter to use a isolator switch separate from the battery terminal rotary one as they tend to corrode due to battery acid and corrosive vapour. The key type one for boats and machinery work well. I also use 200 amp breakers that also act as switches on powered devices, they are made for 4wd winches available in 100 and 200 amp ratings better than fuses if the currant rating suits your application, 200 amp one on 12 volts gives 2400 watts only half your inverter capacity. All the best Bob Foolin Around |
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| paceman Guru Joined: 07/10/2011 Location: AustraliaPosts: 1329 |
Have a look at this thread Balancing in the "Electronics forum. It has quite a lot of info on battery balancing. |
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| ashenash Newbie Joined: 02/11/2012 Location: United StatesPosts: 3 |
Thanks PAceman but the link seems to be dead and I cant find the "balancing" thread by searching the forum. I did however find a good page at http://www.smartgauge.co.uk/batt_con.html which answered many of my questions |
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| paceman Guru Joined: 07/10/2011 Location: AustraliaPosts: 1329 |
Hi Ashenash, Sorry, my mistake - the link is: http://www.thebackshed.com/forum/forum_posts.asp?TID=5120&KW =battery+balancing Greg |
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Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
I'll try to make my post clickable  tinkers 'balancing ' post
Tinker Klaus |
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| paceman Guru Joined: 07/10/2011 Location: AustraliaPosts: 1329 |
Good move Tinker - I can do this OK with "external" links but not sure how to do it easily with forum links - how so? Greg |
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
To add a link to your post, use the  button. It will bring up a popup window that asks first for the screen prompt, like "Click Here", and then the URL, thats the web site address.
You can just post the URL into the message, but the forum software will usually break the URL by inserting hidden spaces. It does that as a security measure. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| Georgen Guru Joined: 13/09/2011 Location: AustraliaPosts: 462 |
Could somebody tell me why I don't get information on what each button does when I go over with mouse pointer? Some are easy to guess like: Bold Italic Underline, rest is bit more difficult for me and by the time I want to post another picture I have to work out how to do it again. George |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Maybe a better question would be ... "Could the forum display information on what each button does when I go over with mouse pointer?" Done. The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| Georgen Guru Joined: 13/09/2011 Location: AustraliaPosts: 462 |
Thanks, I thought it was my fault. (Usually it is  )
George |
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yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
Hi Georgen, The forum is kitted up with mouse-over popup explanations but somewhere along the line the browsers have switched that feature off by default. I use firefox and had to install the feature from their add-on's manager. its called "popup ALT attribute". [Quote] It is a good Idea to be able to isolate each string for testing and equalising charging if necessary. Ashenash Bob's point about isolating the stings is not just a good idea, it is essential, it should be something that is part of the routine every time that a major service is done on the batteries. Multiple strings are fine if you are prepared to be a little fussy. If you isolate a string and draw some power out of it, any problems will become very obvious. You can check voltages and feel for any connections that are getting warm etc, its not possible to do this with the strings all connected together. Follow Bobs great advice and it will be a breeze.  I'm confused, no wait... maybe I'm not... |
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