[RE-wrenches] FLA battery setpoints with larger arrays

[Ray Walters]

Hi Folks;

In our area, below 0F cold is definitely an issue, but I agree it does 
extend battery life if it doesn't freeze.  From a design stand point you 
can end up with a really large battery: double the size to account for 
only discharging it 50% for freeze protection, then double it again 
because it will only have half its capacity when cold.  Freezing is a 
very real problem in subzero weather, and many charge controller's 
default LVD (low voltage disconnect) settings are too low to adequately 
protect the battery.  By the time we see the system, the acid has thawed 
back out, leaked everywhere, and caused all sorts of additional havoc.  
To be fair, this usually happens in systems with DC loads and no LVD.  I 
once saw an indoor battery froze, it was the cell right next to the 
battery vent, which was just a pipe straight through the wall.

Here's some #s for thought from the HUP manual:
Battery acid at 55% discharge can freeze at -15F, which corresponds to a 
steady state voltage of about 12.0 v, on a 12 v system.  A standard LVD 
set to shut off at 11v is too low in this case.

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

On 5/22/2015 6:07 PM, jay peltz wrote:
> Hi Ray,
>
> Cold isn't a problem.  It reduces capacity and yes they could freeze, 
> but it doesn't shorten life ( I mean besides the freezing part) in 
> fact cooler batteries last longer.
> But hot is a problem. Those max temps are not the same thing as 
> reduced life from running at a hotter temperature.
>
>