[RE-wrenches] FLA battery set points with larger arrays

Fri May 22 11:38:57 PDT 2015

Hey guys…

I’ve attached a white paper link that I’ve been working on(below)… This white paper has to do with Rolls Batteries and starting set points… The WP is prerelease and frankly I’m done looking at it as I need to move on to the next.   I don’t think that I’ll ever be accused of being a writer!

The next one will be addressing the changes you will need to make to Off-Grid system settings based on SG, and Load test measurements…   Just a note, I’ve tried to keep the system examples as generic as possible, thanks.
If you have any constructive, or even destructive criticism I will be happy to accept off list at steve at surrette.com<mailto:steve at surrette.com>.

The majority of the systems I see, the batteries are in a state of severe deficit cycling, and undercharged… The root of the problem is, every system the end users are all different, thus if you install the same system in 10 different locations you can get easily 5 different setups.

Yes, I too like to undersize the battery bank, and yes that does tend to use up more water than you would if you had a larger battery bank.   I personally would rather “use up” the battery rather than under use it and have to replace early anyway due to undercharging.

This is where flooded batteries are best… that is if you have the time you can play with the settings…

Adjusting Float voltage a bit higher 2.3vpc instead of 2.2vpc.  This will lower gassing rates, but a higher float voltage could shorten absorb times.

Higher Absorb Voltages, with shorter absorb times.. This will shorten the overall cycle, but may use up water faster…  In colder climates this could be an option.

Lower Absorb Voltage for longer periods. This will lengthen your overall absorb timers, but won’t go thru water as fast.

The gist is… there are many ways to charge a battery….  The bottom line is on systems where you are cycling the battery bank hard  every 1-2 days it’s a good idea to run thru a full absorb cycle about every 7-10 days…  On a system where you are cycling every 4-5 days you can go about 20-30 days between full absorb cycles.

Link to White Paper!..

https://www.dropbox.com/s/bxm8x7456n7g5cg/Technote%20System%20Settings%20for%20Flooded%20Off%20Grid.pdf?dl=0

From: RE-wrenches [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Dan Fink
Sent: Friday, May 22, 2015 10:17 AM
To: RE-wrenches
Subject: Re: [RE-wrenches] FLA battery setpoints with larger arrays

Bill; The Whizbang can mount on the main shunt, and has an included mounting option that lets you piggyback the wires from another amp-hourt meter on it. I have mine with a magnum ME-BMK piggybacked on it.

Dan Fink
Buckville Energy
IREC Certified Instructor™ for:
~ PV Installation Professional
~ Small Wind Installer
NABCEP / IREC / ISPQ Accredited Continuing Education Providers™
970.672.4342

On Fri, May 22, 2015 at 8:28 AM, frenergy <frenergy at psln.com<mailto:frenergy at psln.com>> 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

Steve Higgins
Technical Services Manager
P: +1.902.597.4020
M: +1.206.790.5840
F: +1.902.597.8447
Surrette Battery Company
Exclusive manufacturer of
[cid:rolls656db1]<http://www.rollsbattery.com>

----- 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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