[RE-wrenches] 24 volt Battery Bank comparison
boB Gudgel
boB at midnitesolar.com
Thu Jun 2 17:56:05 PDT 2011
Nobody mentioned this in this thread, but it occurs to me that the
answer may be made clearer
by looking at the Voc of each battery string after so many Amp-Hours
(years) of service.
i.e., disconnect the strings' parallel connection and measure the
individual string voltage after charging them all the best that can be done.
This would be making the assumption that the batteries themselves were
fairly equal capacity and voltage at installation time.
And for whatever reasons, connections, temperatures and everything else
discussed here, the strings degrade differently.
The older and more worn out batteries should have a lower voltage (Voc)
than the less worn out strings. Thus, the better strings
may be tending to hold up the worse strings by dumping charge into them
when the whole bank is discharging,
and wasting energy and battery efficiency.
I guess that just large 2V cells are the answer in this case, if at all
possible.
Thanks for the help on this question !
boB
On 6/2/2011 10:42 AM, Tom Elliot wrote:
> Not surprised at all about the phone company guy. It was a phone
> company guy who read me the riot act that no one in their right minds
> would ever parallel battery banks the way PV off-grid systems did and
> got me to set up my system with separate strings connected
> independently to buss bars. The battery engineer I talked to years
> ago at Dynasty not only said the same thing but also said keeping
> strings separate meant individual string distance from the bars became
> irrelevant (given correctly sized wire for each string’s parallel
> connectors). I had a system with 12 100 amphour strings of paired 12v
> Dynasty AGMs which was rock solid until the day I sold the house.
> The last time I checked the system before the sale no single battery
> varied from any other in the system by more than 1/10 volt and the
> majority were still holding identical voltages.
> *From:* dan at foxfire-energy.com <mailto:dan at foxfire-energy.com>
> *Sent:* Wednesday, June 01, 2011 4:14 PM
> *To:* RE-wrenches <mailto:re-wrenches at lists.re-wrenches.org>
> *Subject:* Re: [RE-wrenches] 24 volt Battery Bank comparison
> Good thread. Thanks.
> In my experience, it all boils down to the customer. I've seen one
> temp. set up with like 12 strings (for a concert). but they were
> recharged and sold individually within a few weeks.. I've also seen a
> single string (Teledyne aircraft batteries) fail in less than a year..
> they were in a brand new airplane tug that was never charged -- ever.
> (the guy said "I dunno, it just stopped working").
> I have one customer who (last I knew) was running 6 strings of mixed
> aged L-16s going on 8 years. Thing is, he's a retired phone company
> dude (Who's missing half of his right hand from using one of those
> pocket pal screwdriver thingys on a key chain in a hot DC rack.. like
> he'd done hundreds of times before.. but that's another tale). But I
> do like his set up.. he has each string set up with it's own fused
> Disco and Trimetric.. Gives him random control over each string. And
> yes, he keeps a very detailed log, and you can bet that when he takes
> a battery out of service, it's done.
> Me? for an average bullet proof off grid system, I shoot for a max of
> two strings for 24V systems (for the redundancy), and manually
> reconfigure them every few years. for 48V systems, I shoot for one
> string of two Volt cells.. thinking that if I loose a cell I can still
> operate a 46V system until I get a replacement.
> And Yes, as we all know, there are folks out there that really
> shouldn't be allowed to operate a popsicle stick.
> db
>
> Dan Brown
> Foxfire Energy Corp.
> Renewable Energy Systems
> (802)-483-2564
> www.Foxfire-Energy.com <http://www.Foxfire-Energy.com>
> NABCEP #092907-44
>
>
> -------- Original Message --------
> Subject: Re: [RE-wrenches] 24 volt Battery Bank comparison
> From: Michael Welch <michael.welch at re-wrenches.org
> <mailto:michael.welch at re-wrenches.org>>
> Date: Wed, June 01, 2011 1:43 pm
> To: RE-wrenches <re-wrenches at lists.re-wrenches.org
> <mailto:re-wrenches at lists.re-wrenches.org>>
>
> Every now and then I see reference on this list to the need for
> thermal detection. Here is an interesting, inexpensive piece of
> equipment that could be used for finding hot (loose or corroded)
> connections, hot batteries, hot PV cells in modules, and even
> poorly insulated spots, its original intended purpose:
>
> http://www.blackanddecker.com/power-tools/TLD100.aspx
>
> I have one and used it for finding uninsulated spaces, but cannot
> attest to its durability or suitability for the other uses
> mentioned above.
>
>
> boB Gudgel wrote at 01:00 AM 6/1/2011:
>
> >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
>
>
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