[RE-wrenches] FLA battery setpoints with larger arrays

[boB at midnitesolar.com]

On 5/22/2015 12:56 PM, Ray Walters wrote:
> 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?


No, but that is on the list as are other things to data log.

Hopefully the temperature is adjusted higher than it would ever get to 
under normal circumstances.

I could see some future systems wanting to be able to regulate Absorb on 
battery temperature mixed with other
parameters some day.   Could get REALLY complicated if you wanted to.  
We're learning more and more
about what is good for batteries.

boB



> 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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