[RE-wrenches] offgrid system question

[Darryl Thayer]

Hi all
Don,t miss Phil's point, The batteries can be good, but be of low surge capacity..... AS phil pointed out, the AH capacity decreases with load, There is a seperate (I am sure related some how) set of unpublished battery surge capacity data, which is not spelled out in the AH capacity until you talk of the 5 min AH perhaps.  If he is surging at 104 Amp 240 volt and 80% eff( will bet eff is less) if this power is being supplied by 44 volts that is 710 DC Amps. The cranking amps are not usually given for solar system batteries.  If some of the math addicted people would do a regression on the numbers Phill gave us perhaps the surge capacity could be indicated.  

Also thanks phill for pointing out thermal runaway potential of VRLA batteries.  

Darryl   


--- On Mon, 8/18/08, jay peltz <jay at asis.com> wrote:

> From: jay peltz <jay at asis.com>
> Subject: Re: [RE-wrenches] offgrid system question
> To: "RE-wrenches" <re-wrenches at lists.re-wrenches.org>
> Date: Monday, August 18, 2008, 7:26 PM
> Hi PHIL,
> 
> Although the batteries may indeed be bad, I would point out
> that the  
> the AC unit is turning on probably when the sun is out,
> therefore the  
> total load isn't all on the batteries.
> 
> And do we know they are XW inverters?
> 
> thanks,
> 
> jay
> peltz power
> 
> 
> On Aug 18, 2008, at 3:18 PM, Phil Undercuffler wrote:
> 
> > My .02 would be a close examination of the batteries,
> and a  
> > realistic realignment of their expectations of their
> capacity.  12  
> > sun extender sealed AGM batteries, 305 AH at 12 vdc,
> wired for 915  
> > AH at 48 volt DC -- sounds like those are the
> PVX-2580.  They’re  
> > only rated 305AH at the 120 hour rate.  If you’re
> hitting that bank  
> > with a fast discharge rate (is 104 amps at 120v or
> 240?), you’ll do  
> > better to consider the bank’s capacity at the 24
> hour rate (258AH)  
> > or even 1 or 2 hour rate ( 165 and 209 AH
> respectively).   
> > Realistically, those three strings of batteries are
> really a 774,  
> > 627 or even a 495 AH bank, depending on how fast
> you’re discharging  
> > them.
> >
> >
> >
> > Make sure the batteries have temperature compensation
> on all  
> > charging sources, and that the batteries are not
> exposed to high  
> > temperatures.  All batteries are affected by
> temperature, but if  
> > VRLA batteries are charged without temperature
> compensation when in  
> > a hot environment they will lose electrolyte which
> cannot be  
> > replaced.  Additionally, ensure all connections are
> good and tight,  
> > and that the bank’s series and parallel connections
> are sized  
> > adequately to handle the surge.
> >
> >
> >
> > Finally, check the LBCO settings on all the XW
> inverters.  I can’t  
> > remember the default setting, but my memory was that
> it is a little  
> > too high – especially when the battery bank is small
> and surge  
> > loads are high.  I worked on a troubleshoot the other
> week where  
> > the installer set the LBCO only a bit below the AGS
> Start DCV 30  
> > second voltage, on an older battery bank of
> questionable capacity.   
> > Unfortunately, the batteries bottomed out before the
> generator  
> > could get started and the system shut down a couple
> times.
> >
> >
> >
> >
> _______________________________________________
> List sponsored by Home Power magazine
> 
> RE-wrenches at lists.re-wrenches.org
> 
> http://lists.re-wrenches.org/listinfo.cgi/re-wrenches-re-wrenches.org
> 
> List rules & etiquette:
> http://www.re-wrenches.org/etiquette.htm
> 
> Check out participant bios:
> www.members.re-wrenches.org