[RE-wrenches] Battery capacity testers

[Dan Fink]

Wrenches;

I have quite a bit of experience with flooded lead-calcium vs. 
traditional flooded lead-antimony battery banks in remote, off-grid 
locations, over the course of the last 15 years. As always, your mileage 
may vary.

On the positive side, lead calcium cells have a low self-discharge rate, 
   extremely low water usage, very long float service life, high 
discharge rate availability, and high DOD available (but not 
recommended). Adding water only every 1-2 *years* is common.

On the negative side, lead calcium cells are intended to live at 80%+ 
SOC for their whole lives, with only very rare DOD of 50%. If buying 
used Pb-Ca cells (for example from a utility or telco switching station) 
each DOD of more than 80% SOC is documented in writing. Banks must be 
sized much larger than lead-antimony to prevent this. Also, battery 
voltages are lower, and charging and equalization regimes are far 
different. Some charge controllers, inverters, other equipment, etc. do 
NOT have settings to use Pb-Ca, some do.

In the best case scenarios I've dealt with here (oversized battery bank 
of surplus cells), I've seen 10+ years service life from *used* cells. 
In the worst case scenarios, life of less than 2 years (too many deep 
DOD cycles).

DAN FINK
Buckville Energy Consulting LLC

Mark Frye wrote:
> Todd,
>  
> Can you give us a comparison of lead vs lead cadmium?
>  
> My understanding is that lead cadmium are suited for standby operations 
> such as telecomm back up.  That means spending most of the time in 
> float, with occasional short term high discharge rate with very high DOD 
> available.
>  
> How well do they cross over into a daily-cycle off-grid situation with 
> moderate daily DOD?
>  
> Mark Frye
> Berkeley Solar Electric Systems