Re: [RE-wrenches] Strings and series of batteries

[Kent Osterberg]

Hugh, Feeding off diagonal corners, as you are describing, only keeps the wire resistance of the parallel paths balanced when there are two parallel strings of batteries and the connections between the batteries are all the same length (or at least they add up to the same total length).  With three or more parallel paths, the resistance of the wire is going to cause imbalanced current between the parallel paths.  But the internal resistance of the batteries is important too.  Unfortunately even with bus bars and equal length wires, imbalances between the parallel paths will develop because of the batteries' internal resistance.  Consider what happens when a battery gets sulfated: its voltage goes up quickly while charging and it goes down quickly while discharging -- in other words: its internal resistance goes up.  Despite our best attempts to keep the wire resistance balanced, some cell will sulfate more quickly than the others, then it is a down hill spiral with the current balance getting worse and worse.  With paralleled batteries keeping them equalized becomes critical and the more parallel paths there are - the harder it is to get them all equalized. Kent Osterberg Blue Mountain Solar www.bluemountainsolar.com Hugh wrote: Tom, Sorry, I failed to write clearly. I was not talking about bus bars in this sentence.  I meant to say that I 'daisy chain' links from one string to the next.  I parallel them by connecting A to B, B to C, C to D.  Then I connect positive of A to the inverter, and negative of D to the inverter.  In this way the connections are all balanced without the use of a bus bar.  You can connect the positive of D to the wind turbine (and the negative of A) to reduce the danger of a direct connection without batteries. If a battery is well charged I see no problem with parallel strings. As it gets older then you do need to monitor the individual cells/units for failures and take action.  Standard smaller sized units are easier to re-group, and if desired to replace. Tom wrote: "If you connect links  between all of the positives, and links between all of the negatives, to parallel the battery, then the only issue is where you connect the charge source and/or inverter." Hugh, The connection is very easy, if you look at the photos on the page I linked to the connections to the inverter breaker (which is where I also connected the charge source) come off the bus bars.  It's actually a very simple installation and I found it much easier and safer to work on that a large series/parallel bank of L-16s, which was what my first bank in that system consisted off and it turned out to be a mess (designed and the components built by Jade Mountain...) Tom -------------------------------------------------- From: "Hugh" <h...@scoraigwind.co.uk> Sent: Thursday, December 03, 2009 8:30 AM To: "RE-wrenches" <re-wrenches@lists.re-wrenches.org> Subject: Re: [RE-wrenches] Strings and series of batteries Just for a contrasting opinion: I rarely use grease or vaseline unless it proves necessary.  I have changed out battery banks after seven years and the connectors are still pristine whilst dry.  I agree that sometimes there will be localised corrosion on battery terminals.  I find it rarely, and I deal with it as and when.  I might use vaseline then.  Or spray on some oil.  Not a big deal to be honest.  The contact resistance is not affected by corrosion on the outside.  Probably due to some moisture arriving on the terminal?  But vaseline/grease attracts dust, makes a big mess and mess is not nice around batteries. Bus bars sound great, but what a hassle.  If you connect links between all of the positives, and links between all of the negatives, to parallel the battery, then the only issue is where you connect the charge source and/or inverter.  I have learned to connect them at opposite ends of the parallel links.  'Diagonally opposite' you could call it.  In this way the resistance is identical to each string. One string has a direct connection to plus.  One has a direct connection to minus.  All have equal number of links between them and the inverter.  If there is a wind turbine then I will often connect this to two corners and the inverter to the opposite two corners, making it very difficult to (both) disconnect the battery and (also) leave the wind turbine connected to the inverter.  This probably has saved a few inverters from instant death due to carelessness. -- Hugh Piggott Scoraig Wind Electric Scotland http://www.scoraigwind.co.uk _______________________________________________ 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 No virus found in this incoming message. Checked by AVG - www.avg.com Version: 9.0.709 / Virus Database: 270.14.91/2542 - Release Date: 12/02/09 21:32:00 _______________________________________________ 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 No virus found in this incoming message. Checked by AVG - www.avg.com Version: 9.0.709 / Virus Database: 270.14.92/2543 - Release Date: 12/03/09 11:36:00

_______________________________________________
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