c-40 battery charging [RE-wrenches]

Matt Tritt solarone at charter.net
Sat Oct 11 12:33:16 PDT 2003 

Wow! No wonder the danged thing caught fire! This sounds like another
one of those totally wrong from the start jobs. Was the battery bank
charged with an old Jake? Why 120 volts? The 48 volt banks were trying
to bring the 24 volt bank up to the same voltage, that's why it went
gonzo. Any fusing on the 24 low voltage string would have to be so large
that it wouldn't be effective for the intended purpose. This situation
undoubtedly produced enough hydrogen to cause a sizable explosion.

Matt T

-----Original Message-----
From: Darryl Thayer [mailto:daryl_solar at yahoo.com] 
Sent: Saturday, October 11, 2003 11:57 AM
To: RE-wrenches at topica.com
Subject: Re: c-40 battery charging [RE-wrenches]


I am not sure but i think that flooded cells are
different than AGM.  An AGM is where I have heard and
seen thermal runaway.  

However I have experienced a Fire situation with
flooded batteries, on two occasions.  First is where a
customer had a different wrench install two parallel
strings of 120 volts. Because of SW5548 being 48 volts
the string was broken into two 48 volt sections and
one 24 volt section.  The string became unbalanced and
the 175 amp + charging current the full batteries
boiled, acid on top spread to adjacent batteries, a
short occurred and the batteries caught fire. When the flashover
occurred, it was internal to the one string and I am not sure if fuses
would have helped.  This is similar to what happens during forming of
batteries. 
( I have been told that during forming, battery fires
sometimes occur.)
\
The other flooded case is when a loose connection
overheated and ignited a Styrofoam and wood battery
box.  

Of course we have all seen hydrogen explosions, which
I put in a different category.

Daryl

--- Greg Egan <gegan at renewalaska.com> wrote:
> Matt,
> 
> I've only worked on 30 or so large battery back ups
> for emergency
> lighting applications. I've never seen any of them
> fuse each string 
> either. My guess is cost. It's not required by UL,
> and these banks were 
> not in dwelling units like mine are. The other
> reason may be that these 
> strings were all enclosed in metal cabinets.
> 
> I've never seen an AGM or any other battery catch on
> fire but I believe
> the wrenches on this list who say they did. Maybe
> fusing each string is 
> overkill. However, none of the banks I've installed
> are in metal 
> cabinets, and most of them are in peoples' homes.
> 
> Personally, the only reasons I can think of to fuse
> each string
> individually would be if it's mission critical
> equipment or it's in a 
> dwelling unit.
> 
> Best,
> 
> Greg
> 
> 
> 
> Matt Tritt wrote:
> > I see your point. I suppose my question would be
> related to what I've seen
> > in large battery installations in various crirical
> off-grid and backup
> > installations; that is, if fusing individual
> strings seems to be such a good
> > idea, why isn't it a standard procedure in large
> arrays? Buss bars are.
> > 
> > Matt T
> > ----- Original Message -----
> > From: "Greg Egan" <gegan at renewalaska.com>
> > To: <RE-wrenches at topica.com>
> > Sent: Friday, October 10, 2003 11:23 AM
> > Subject: Re: c-40 battery charging [RE-wrenches]
> > 
> > 
> > 
> >>Matt,
> >>
> >>Unless I'm missing something, the buss bar doesn't
> prevent one string
> >>getting overcharged by the other strings. The way
> I understand it, if
> >>string "A" has some kind of a short, parallel
> strings B & C will try to
> >>charge it. If we only have a fuse between the buss
> bar and the DC
> >>disconnect, it doesn't protect against overcurrent
> when one or more
> >>strings are charging the shorted string.
> >>
> >>Greg
> >>
> >>
> >>
> >>Matt Tritt wrote:
> >>
> >>>I think that with multiple strings the buss bar
> plan is the way to go to
> >>>avoid having to fuse each string. If there is no
> reason for any one
> >>>string to take too much current the need for an
> individual string to
> >>>have a fuse is negated. This is so weird. I used
> to connect all my
> >>>parallel strings to a common buss until just a
> few years ago. A big
> >>>battery guru told me it wasn't necessary.
> >>>
> >>>The more things change the more they stay the
> same.
> >>>
> >>>Matt T
> >>>
> >>>-----Original Message-----
> >>>From: William Miller [mailto:wrmiller at slonet.org]
> >>>Sent: Friday, October 10, 2003 1:38 AM
> >>>To: RE-wrenches at topica.com
> >>>Subject: Re: c-40 battery charging [RE-wrenches]
> >>>
> >>>
> >>>Learned Colleagues:
> >>>
> >>>
> >>>Would it be advisable to install a class T fuse
> between strings?
> >>>
> >>>William Miller
> >>>
> >>>
> >>>
> >>>
> >>>At 08:39 PM 10/10/2003 +1300, you wrote:
> >>>
> >>>
> >>>>I have seen the result of an AGM meltdown.  It
> was a telecom
> >>>>installation and one block went bad, the rest
> discharged into it and
> >>>>the result was an unbelievable mess.  One string
> is the way to go.
> >>>>
> >>>>Cheers,
> >>>>Bruce Geddes
> >>>>PowerOn
> >>>>
> >>>
> >>>
>
>>>__________________________________________________________________
> >>>William Miller
> >>>Miller Power and Communications
> >>>PO Box 50, Santa Margarita, CA 93453
> >>>Voice :805-438-5600     Fax: 805-438-4607
> >>>email: wrmiller at slonet.org
> >>>http://millerpowerandcomm.com
> >>>License No. C-10-773985
>
>>>_____________________________________________________________
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