[RE-wrenches] 24 volt Battery Bank comparison

[Ray Walters]

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 <ray at 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, dan at 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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