AGM battery strings: Problems? [RE-wrenches]

[Kelly Keilwitz]

Hi Doug,
Thanks for the encouragement. I also received the following feedback
off-list from Dan, a Sr. Engineer with Exeltech (who prefers to stay in the
background, but agreed to let me post it) :

quote:
" .... batteries must be
substantially different in age and/or condition before paralleling
two different strings is an issue. You
can parallel the two strings you described without worry.

First, the battery systems are within months of each other in age, so
that's not a problem.  They must be -years- apart and/or
significantly different in health before paralleling is ruled out.
#2 .. despite the differences A-H ratings, the two paralleled strings
will share current flow proportionately based on their rated
capacities.

Connect the strings as you would any other series/parallel
configuration with +/- connected in opposite corners - you'll have a
193 A-H battery.   Follow the charge specs from the AGM mfgr
including the temperature compensation - you'll be fine."

Dan went on to say that he has several sets of AGM's, some as old as 20
years, and has 35+ years of experience with batteries.

-Kelly



On 12/2/06 8:45 AM, "Doug Pratt" <dmpratt at sbcglobal.net> wrote:


> Kelly, there's more shades of grey than absolute yes or no rules when it
> comes to batteries. Although it isn't ideal, your two strings are so similar
> that problems should be beneath notice. Same manufacturer, similar age,
> slight difference in capacity. You're right, the worst case is that the
> larger string loses a bit of capacity. This combined pack will be fine using
> single cabling. 
> 
> Cheers,
> Doug Pratt
> DC Power Systems
> 
> 
> -----Original Message-----
> From: Kelly Keilwitz [mailto:kelly at whidbeysunwind.com]
> Sent: Friday, December 01, 2006 4:55 AM
> To: RE Wrenches listserve
> Subject: Re: AGM battery strings: Problems? [RE-wrenches]
> 
> 
> Jim,
> I know problems are possible, but was hoping that the voltage/resistance of
> the two strings will be alike enough that the problems would be minimal.
> What's the worse case - that the capacity of the larger string falls to that
> of the smaller? We might be willing to put up with that. Or, is premature
> failure a real possibility?
> 
> This is a grid-tie, hands-off, will-work-automatically-guaranteed, backup
> system. So, switching between banks for won't work here.
> 
> 
> On 11/30/06 1:02 PM, "Jim Easton" <jim at altenertec.com> wrote:
> 
>> 
>> Possibility of problems? Yes.
>> 
>> Paralleling batteries of dissimilar type/history can lead to premature
>> failure & lack of anticipated capacity.
>> 
>> A better solution might be to use an A-B switch with a battery isolator
>> for
>> charging.
>> 
>> Jim Easton
>> Alternative Energy Technologies
>> CSL: 852243
>> 9465-B Mission Park Place
>> Santee, CA 92071
>> Tel: 619-262-8800
>> Fax: 619-562-8811
>> Cell: 858-527-0240
>> 
>> -----Original Message-----
>> From: Kelly Keilwitz [mailto:kelly at whidbeysunwind.com]
>> Sent: Thursday, November 30, 2006 8:20 AM
>> To: RE Wrenches listserve
>> Subject: AGM battery strings [RE-wrenches]
>> 
>> 


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