Hi Kent,
I am sorry but I disagree with your conclusion that it only keeps the
wire resistances the same for 2 strings. This diagonal system, which
I believe many people would call 'reverse return' in the states,
actually provides for exactly equal resistance on all paths to all
strings. Each time you add a link in the positive path you remove
one in the negative path. I admit that the voltage drops will be
very slightly different due to different currents in the various
links but the differences now are so tiny that I would not worry
about them.
I agree that you will get imbalances in multiple battery strings at
times - usually during periods of prolonged low winds. But you
cannot persuade me that multiple strings 'don't work right' because
they are used in most of the systems I work with since the 1970s. I
see just as much sulphation in large capacity cells as I do in small
capacity cells (in multiple parallel strings). I would say that
going from 12-volts on up to 48-volt systems has caused me a lot more
headaches with unequal battery states than paralleling a lot of
batteries has. Batteries connected in parallel will tend to take
what they need. Connected in series they take what they are given.
Also, a cell failure in a 12-volt system attracts attention at once,
whereas a cell failure in a 48-volt system can be overlooked for much
longer.
There are plenty of points of view about batteries :-) Part of it is
the difference in mentality between solar users (who count out the
amp hours and know exactly what they have to work with each day) and
wind users (who can party like mad sometimes and then have nothing at
other times).
Hugh
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
<http://www.bluemountainsolar.com/>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" <mailto:[email protected]><[email protected]>
Sent: Thursday, December 03, 2009 8:30 AM
To: "RE-wrenches"
<mailto:[email protected]><[email protected]>
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>http://www.scoraigwind.co.uk
_______________________________________________
List sponsored by Home Power magazine
List Address:
<mailto:[email protected]>[email protected]
Options & settings:
<http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org>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>http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org
List rules & etiquette:
<http://www.re-wrenches.org/etiquette.htm>www.re-wrenches.org/etiquette.htm
Check out participant bios:
<http://www.members.re-wrenches.org>www.members.re-wrenches.org
No virus found in this incoming message.
Checked by AVG - <http://www.avg.com>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:
<mailto:[email protected]>[email protected]
Options & settings:
<http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org>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>http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org
List rules & etiquette:
<http://www.re-wrenches.org/etiquette.htm>www.re-wrenches.org/etiquette.htm
Check out participant bios:
<http://www.members.re-wrenches.org>www.members.re-wrenches.org
No virus found in this incoming message.
Checked by AVG - <http://www.avg.com>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: [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
--
Hugh Piggott
Scoraig Wind Electric
Scotland
http://www.scoraigwind.co.uk
_______________________________________________
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
