[RE-wrenches] FLA battery setpoints with larger arrays

Fri May 22 12:56:14 PDT 2015

Hi Bill;

If the battery is in an insulated box indoors, it definitely can over 
heat.  Also if ambient temps get into the 90s, the additional heat from 
charging can push the battery into the danger zone.  In hot desert or 
tropical climates, it may actually be difficult to keep the battery 
below 105F.
I'm very glad to hear Midnite added the high temp disconnect to their 
system.  They may have saved a life.
Bob, is battery temp logged, so we could see how often a system quits 
charging for high temp, and just what the battery temps are running?  
Many of our systems may need additional cooling.  A recent HUP install 
in Haiti comes to mind.....

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

On 5/22/2015 8:28 AM, frenergy wrote:
> Hey Jay,
>         From what I've heard form battery manus, the C rates likely 
> even in a well PV-ed system still will not produce C-rates high enough 
> to approach a high or "longevity reducing" internal battery temp, 
> assuming a typical bulk, absorb, float cycle.  Of course, battery 
> environmental location (typical temps) would set a baseline from which 
> batt temp would rise from.  Here in the Sierra, ambients are not very 
> high 95% of the time.
>         Just curious, how does the wiz bang account for all loads...2 
> shunts?
> Thanks,
> Bill
> Feather River Solar Electric
>
>     ----- Original Message -----
>     *From:* jay peltz <mailto:jay.peltz at gmail.com>
>     *To:* RE-wrenches <mailto:re-wrenches at lists.re-wrenches.org>
>     *Sent:* Thursday, May 21, 2015 8:07 PM
>     *Subject:* Re: [RE-wrenches] FLA battery setpoints with larger arrays
>
>     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 <mailto: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 <mailto: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 <tel:505%20780-2738> cell*
>
>
>
>     -- 
>     Jay Peltz
>     Peltz Power
>     jay.peltz at gmail.com <mailto:jay.peltz at gmail.com>
>
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