[RE-wrenches] 4 ways to keep a battery for a long time

[Ray Walters]

Hi Larry and Jay;

I totally agree, that taking into account charge and discharge rates, 
DOD, and temperature, we should be able to more accurately model a 
battery's lifespan.   We already have temp sensors at the battery, so it 
seems just a matter of software to do this.  Also battery's nonlinear 
behavior is well known and easily modeled.

This is a huge issue with modeling software like HOMER, as well.  I 
tried to bring this discrepancy to HOMER staff's attention, and they 
said I needed to purchase their consulting package on top of the $400/ 
yr software license.  Such arrogance is really just ignorance: to not 
model battery temperature?  I was told that they assumed all battery 
banks would be in temperature stable rooms. (Boy, that's a Unicorn 
assumption, made by engineers that probably have never even seen an off 
grid system)
  I have systems in Wyoming at 20 below, and others in Haiti's 
sweltering heat, but according to all known software modeling and 
metering, the 2 systems' batteries are identical.  In reality of 
course,  one is going to freeze and crack the cells, while the other is 
going to boil over and die an early death from heat exhaustion. Neither 
outcome apparently is predictable, except by us grey haired old know 
nothings.  (I too have a degree in Engineering, and it took almost 10 
years of hard off grid experience to overcome the brain washing)

At least Midnite has included a high temperature disconnect for the 
batteries, which is a great idea.  Most batteries do not want to go over 
105F, and halting charging till the temp comes down will definitely save 
some batteries.  I just had a large forklift set that stayed on an 
uncontrolled charger too long. The entire pack was at 110F and it took 
several hours to cool down below 100F.  Room temp was 75F.
Its also very possible to predict a battery's freeze point, and 
disconnect the load  based on voltage, SOC, AND temperature.

I think everyone is afraid to throw too much brain power at modeling 
lead acid batteries that may become obsolete, but as far as I can tell, 
every other storage chemistry has similar characteristics: lower 
capacity at low temps, a high temp limit, non-linear cycle life 
depending on DOD,  Puekert's exponent relating capacity vs charge/ 
discharge rates, volt drop under hard discharge, etc.

R.Ray Walters
CTO, Solarray, Inc
Nabcep Certified PV Installer,
Licensed Master Electrician
Solar Design Engineer
303 505-8760

On 12/17/2015 8:26 AM, Starlight Solar Power Systems wrote:
> Jay,
>
> But that data does not consider the non-linearity of the DoD/Cycle life relationship.  One grossly neglected item in battery monitors is the tracking of operating temperature.
> By daily monitoring and logging temperature and DoD and charge rate and kWh removed and EQ cycles, days deficit charged, and, and... we should be able to model accurate end of life for any battery.
>
> Larry Crutcher
> Starlight Solar Power Systems
>
>
>