[RE-wrenches] 24 volt Battery Bank comparison

Ray Walters ray at solarray.com
Fri Jun 3 10:53:57 PDT 2011


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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