[RE-wrenches] 24 volt Battery Bank comparison
boB Gudgel
boB at midnitesolar.com
Thu Jun 2 09:32:26 PDT 2011
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 <mailto: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 <mailto: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 <http://www.positiveenergysolar.com/>
>
> On 6/1/2011 9:20 AM, toddcory at finestplanet.com
> <mailto: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> <mailto: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> <mailto: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 <mailto:boB at midnitesolar.com>
> **Sent:**Tuesday, May 31, 2011 8:16 PM
> **To:**RE-wrenches <mailto:re-wrenches at lists.re-wrenches.org>
> **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 <mailto:wayne at pureenergysolar.com>>
> wrote:
>
> I think the verdict is**12** - 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 <mailto:Wayne at PureEnergySolar.com>
> http://pureenergysolar.com
> 352 377-6527 Office
> 352 336-3299 Fax
> 352 316-1637 Cell
>
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