[RE-wrenches] FLA battery setpoints with larger arrays

[jay peltz]

Hi Allan,

I like the classic/wiz bang jr.  This allows really good end amp control as
all loads are accounted for.

Higher C rates equal higher internal temps which definitely will shorten
the life.

On Thu, May 21, 2015 at 10:56 AM, Allan Sindelar <allan at sindelarsolar.com>
wrote:

>  Wrenches,
> In the last few years I have changed my approach to off grid system
> sizing, primarily due to higher battery costs and lower module costs.
> Rather than shooting for a traditional 80-90% of winter load profile
> target, I will size a larger array and smaller battery bank, figuring
> (especially here in the sunny Southwest) that batteries will recharge more
> quickly, will spend more of their time full (and thus last longer), and
> will be at least partially charged during cloudy weather. This even allows
> for smaller battery banks that are cycled more deeply (as long as there's a
> backup gennie in the mix); the lower cost of a smaller size may allow for a
> set of higher-quality industrial cells.
>
> I first began to rethink my design approach after reading Christopher
> Freitas' Solar Pro article on large battery banks a few years ago. Being
> able to refill in a day was part of his strategic approach to battery bank
> design. I used and wrote about this approach in my tiny house article in
> the current Home Power. However, I'm just beginning to get owner feedback
> about greater water consumption and the need for more frequent watering.
> This is especially the case when I add array to an existing system, and the
> old watering schedule is suddenly not enough.
>
> When I design new systems I now encourage larger arrays and smaller
> battery banks, as the batteries spend more of their time happily full and
> recover more quickly after a discharge period. But I am thinking that I
> will have to begin changing charging setpoints in response. Flooded
> batteries have a range of recommended bulk setpoints, from 28.8 to 29.6
> volts on a 24V system. When arrays were smaller we set to the higher end of
> the range to take advantage of topping off when available, and a two hour
> or longer absorption was considered beneficial, as long as the CC could
> transition to float at 2% of capacity or so. With a larger array a better
> approach may be to lower the bulk/absorption setting, as well as reduce
> absorption time and raise the float transition current ("done amps").
>
> I'm writing to encourage a discussion among off grid Wrenches. Are you
> changing the relative relationship between array and battery capacities? If
> so, how are you adjusting charge controller setpoint programming? For
> example, how would you program a Midnite Classic, Outback FM or Schneider
> XW if you could achieve a C/10 or C/15 charge rate?
>
> Thanks, Allan
>
> *Allan Sindelar*
> allan at sindelarsolar.com
> NABCEP Certified PV Installation Professional
> NABCEP Certified Technical Sales Professional
> New Mexico EE98J Journeyman Electrician
> Founder (Retired), Positive Energy, Inc.
> *505 780-2738 <505%20780-2738> cell*
>
>
>

-- 
Jay Peltz
Peltz Power
jay.peltz at gmail.com
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org/attachments/20150521/aac03863/attachment-0002.html>