[RE-wrenches] 24 volt Battery Bank comparison

Darryl Thayer daryl_solar at yahoo.com
Thu Jun 2 09:47:57 PDT 2011


it  is due to differences in the strings; in charging and in discharging differentials.  this is due to temp differences very small differences in connections and differences in the cells themselves.  

Darry



________________________________
From: boB Gudgel <boB at midnitesolar.com>
To: Darryl Thayer <daryl_solar at yahoo.com>; RE-wrenches <re-wrenches at lists.re-wrenches.org>
Sent: Thursday, June 2, 2011 11:32 AM
Subject: Re: [RE-wrenches] 24 volt Battery Bank comparison


On 6/2/2011 9:03 AM, Darryl Thayer wrote: 
Excellent comment tom, so true.  I get concerned that some of my experiences are a collection of exceptions.  I like Larry's comments because he has worked so many systems.  I have seen fires, but  mostly because I have a reputation and people wnat me to come and see what happened.  
>
>Darryl
>
>
>
Now my question would be...  Why ?

I have to think that with more batteries in the system, they are
    just not getting charged as well.

If that's the case, I think this could be fixed. Haven't battery
    chargers and education gotten
better since 1967, Tom ?

boB




>________________________________
>From: The Solar Powered Office of Tom Duffy <tom at thesolar.biz>
>To: Allan at positiveenergysolar.com; 'RE-wrenches' <re-wrenches at lists.re-wrenches.org>
>Sent: Thursday, June 2, 2011 9:34 AM
>Subject: Re: [RE-wrenches] 24 volt Battery Bank comparison
>
>
> 
>Wrenches:
> 
>This is a really great thread. Here’s my two cents…
>I started selling and configuring battery systems when I got out of the Army back in 1967 I’m a marine electrician. In the boat environment everybody tries to make a big battery out of a bunch of small batteries, Over the years this is what I’ve witnessed; All else being equal.
>3 parallel strings = 4 ½  to 5 ½ years Max
>2 parallel strings = 5 ½ to 6 ½ years Max
>1 series string = 8 to 12 years Max
>The above seems to hold true if the charge settings, Bulk, Absorb time and Voltage are correctly set. But as we all know 85% of the time this is not the case.
>So my conclusion is that parallel configured banks just about cut the life in half. 
>And there is always the stories about the guy that drank a quart of Bourbon a day and smoked cigars chasing women until he was 102 years old. The same is true with batteries… the exception but not the rule.
> 
> 
>  Tom Duffy
>  Systems Design Engineer
> 
>     tom at thesolar.biz
>       575-539-2111 X 122
>Although no trees were killed in the sending of this message, a large number of electrons were terribly inconvenienced.
> 
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>________________________________
> 
>From:re-wrenches-bounces at lists.re-wrenches.org [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Allan Sindelar
>Sent: Wednesday, June 01, 2011 11:07 PM
>To: re-wrenches at lists.re-wrenches.org
>Subject: Re: [RE-wrenches] 24 volt Battery Bank comparison
> 
>I had done this a few times in the distant past, and also had done it in recent years on my own previous battery bank (four strings of S-530s - yes, I know; it was in anticipation of future plans to upgrade to 48V, and two strings wouldn't have been enough).
>
>It worked fine - and that turned out to be a
                      problem. I had noticed reduced
                      capacity, but assumed foolishly that it was simply
                      to age and cycle life (going
                      on six years and three teenagers). Found out I had
                      two failed cells in two
                      different strings. The parallel connections
                      probably - I'm not sure here -
                      allowed the bank to perform more robustly and less
                      obviously weakened. It might
                      have even allowed the bank to perform as if both
                      failed cells had been in the
                      same string. But it also allowed me to not pay
                      enough attention to a
                      potentially serious problem by disguising it.
>
>I blame myself more than the parallel connectors
                      (just some #2 interconnects I
                      had lying around). I'm just not sure I would use
                      it on a customer's system.
> 
>Allan Sindelar
>Allan at positiveenergysolar.com
>NABCEP Certified Photovoltaic Installer
>NABCEP Certified Technical Sales Professional
>New Mexico EE98J Journeyman Electrician
>Positive Energy, Inc.
>3201 Calle Marie
>Santa Fe , New Mexico 87507
>505 424-1112
>www.positiveenergysolar.com 
> 
> 
>
>On 6/1/2011 9:20 AM, toddcory at finestplanet.com wrote: 
>Does it make any difference to do as boB recently suggested and inter-connect the strings? So in other words, if you have two parallel strings, what happens if you parallel each battery in one string with the battery in the other string? Has anyone tried this? It might help insure more balance between each series string.
> 
>Todd
> 
> 
> 
>On Wednesday, June 1, 2011 3:06am, "James Surrette" <james at surrette.com> said:
>Hi boB,
> 
>I would say maintenance is a large issue - especially when dealing with L-16's or the like, as the number of cells & connections gets large, i.e. 1000-1200AH @ 48VDC is three (3) strings, 24 batteries and 72 cells.  Will a client water 24 cells...maybe - 72??
> 
>However, from Tech Support days, imbalance is the larger problem.  It seems to take 18 months - 3 years and then you would get SG readings where one (1) bank was perfect and the other(s) is significantly lower......which is hard to overcome without effort (either break the banks & charge independently or hammer the banks and allow the high string to get even higher). 
> 
>One of the key take aways that often gets overlooked is the proper initial activation of the strings.  It is impossible for all cells to have identical resting voltage.  During commissioning, each string should be charged to 2.45-2.5VPC and held until all cells read the same voltage.  If running multiple strings, then connect the strings and run the entire bank at 2.45-2.5VPC until all cells measure the same voltage.  Now the bank is well balanced and the chances of a major imbalance are greatly reduced.  However, even after this effort, if you use an amp clamp, you will notice slight differences in the amount of current being accepted by each bank.
> 
>Best,
> 
>Jamie
>
>
>
>
>>>> boB Gudgel <boB at midnitesolar.com> 6/1/2011 5:00 AM >>>
>On 5/31/2011 11:25 PM, Tom Elliot wrote:
>Bob,
>> 
>>I totally understand the concern about multiple strings *if the strings are connected across the battery bank* as had always been the tradition in off-grid installations.  My own experience with such a bank in my system  showed why when I had a single cell get to near meltdown.  I was lucky to find it.
>
>
>This might be a good reason for an installer to
                        have one of those FLIR (or
                        similar) thermal imager cameras.   They're a bit
                        on the expensive
                        side, but could
>really be helpful for so many things.   Even
                        just to know if you have
                        left a nut loose (under load of course)
>
>boB
>
>
>
>Maintenance is another reason, such banks are far more difficult to maintain.  But I think those concerns are ameliorated a great deal with a buss bar installation and once I did that I never had another problem and found the battery bank much easier to maintain because the strings no longer had to be right next to each other.  Heck, it would be possible to put each series string in its own box for that matter.  And with the inclusion of string fuses that reduces problems even further.
>> 
>>When living with an off-grid system my biggest concern was system reliability and redundancy and the idea of a single string failure was a big worry which is why I never would consider it.
>> 
>>Tom
>> 
>> 
>> 
>>From:boB Gudgel
>>Sent:Tuesday, May 31, 2011 8:16 PM
>>To:RE-wrenches
>>Subject:Re: [RE-wrenches] 24 volt Battery Bank comparison
>> 
>>
>>
>>OK, I've been hearing for years now that
                                one battery string is best and maybe
                                two but no more should be used.
>>
>>What is the reason for this fear ???   
                                What is the experience
                                with multiple strings in parallel ??
>>
>>If it is because of current sharing of
                                the strings, that shouldn't be an
                                insurmountable problem if the wiring is
                                done right.
>>
>>If it has to do with the possibility of
                                fire, which Darryl mentioned, seems
                                that series string fuses could mitigate
                                the possibility of that issue, if
                                because of shorted cells, just like PV
                                combiners.
>>
>>Or maybe it has to do with the trouble
                                of getting into the middle of a pile of
                                batteries ?  Use battery boxes ?
>>
>>The strings are in parallel and so they
                                all get the same voltage, theoretically
                                anyway if the connections are good.
>>
>>I would think that the more strings, the
                                LESS stress on individual batteries,
                                not more.  The current in each battery
                                should be less than it would be I
                                would think.
>>
>>So what is the real experience ??
>>
>>Is a battery balancer the answer ??
>>
>>Thanks,
>>boB
>>
>>
>>
>>
>>
>>
>>>On May 31, 2011, at 8:23 PM, "Wayne
                                    Irwin" <wayne at pureenergysolar.com> wrote:
>>>I think the verdict is12 - Rolls 2-YS-31 2430 AH @ 20 HR (one string) and one dry spare in storage is the best case scenario!
>>>>
>>>>Wayne Irwin, EE
>>>>Director of Engineering
>>>>Pure Energy Solar International
                                      Inc. 
>>>>State Licensed Solar Contractor
>>>>License # CVC56695 
>>>>Wayne at PureEnergySolar.com
>>>>http://pureenergysolar.com
>>>>352 377-6527 Office
>>>>352 336-3299 Fax
>>>>352 316-1637 Cell
>> 
>> 
>> 
>>
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