So would you agree that battery inequalities show up more at:
a) high discharge/charge rates (greater than C5)
b) higher battery voltages (more cells in series, over 48v)
c) more parallel strings
d) bad/ corroded/ loose connections
e)lack of initial EQ/ activation charge and periodic EQ after long or
heavy discharges
f) main cables not at least wired to opposite sides of battery bank or
better: separate parallel cables to buss bar
h) lack of maintenance (watering, uneven cell temperatures)
Did I miss anything?
Ray
On 6/3/2011 12:10 PM, James Surrette wrote:
Hi Ray,
Just a quick chime in on your series string comment.
If you hook up 4 x 12V monoblocks for a small 48VDC system and begin
charging at 58.8V, total voltage will be 58.8V very quickly but
individual battery voltage will not be 14.7V. Battery voltage will
have a large range from 14 to almost 17V. This problem is only
exacerbated in higher voltage systems, ie, Australian 120VDC.
Stealing from the Telcos, the best solution is an initial activation
to balance all cells. When this is completed and assuming all leads
stay tight, no bad cells, etc the bank will charge and discharge in
relative harmony. However, if the cells / batteries are bolted
together and discharged right out of the gate, there's a good chance
SG & Voltages will be all over the map in short order.
Jamie
>>> Ray Walters <r...@solarray.com> 6/3/2011 2:53 PM >>>
I've set electric vehicle parallel strings up like this too. Once a
month I charge each string separately. At higher charge/ discharge
rates, the problems of unequal batteries increases dramatically. BTW,
single strings are not the magic bullet either; I've had single
strings with equal current through each battery, but some batteries
would be at 15.5 volts, while others next to it would be at 13. The
charge controller shuts off when the sum of the voltages hits the bulk
charge V, but meanwhile some cells are chronically overcharged or
undercharged. (parallel strings no where to be seen)
Manzanita Micro makes a device that shunts current past batteries that
hit full charge in a string. This monitoring of each individual
battery is the state of the art right now for Li+ batteries in EVs.
I agree, we need much better battery management and safety devices for
solar. Its ridiculous some of the mundane issues we discuss here
sometimes, while hundreds of huge battery packs are just waiting for
one of us to drop a wrench across the terminals, with zero safety to
interrupt it, and its all NEC compliant.
Batteries themselves need to have a current limiting device built into
the positive terminal. Possibly the same device that controls charge
current to it too?
Dreaming up future BOS equipment,
Ray Walters
On 6/2/2011 7:44 PM, d...@foxfire-energy.com wrote:
What I like best about Mark's set up (the retired phone co. dude w/
half a hand), is that he can select individual strings at random. he
can eq an individual string, or top off a few strings and park them.
he can even run strings of T 105s, or even nicad (individually of
course) in the same system as L-16s and the like.. he just reprograms
the chargers (and logs it). I think he got the design from his days
in the Navy.
So boB, how about a controller that can be user programed to charge
multiple battery configurations with a soft switch? i.e. Bank A, Bank
B...? and while you're at it, maybe a multiple string DC box?
Something with a shunt and a breaker for each string? A four string
set up would be nice.
I could use 2% of your first million.
db
Dan Brown
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