General AGM Battery SOC/Overnight Guidelines

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JPSolarZap
Forum Member
Posts: 13
Joined: Tue Feb 27, 2018 10:06 pm
My RE system: 7800w of array, flexpower 2 vfxr3648, 16 6v AGM 400ah

General AGM Battery SOC/Overnight Guidelines

Post by JPSolarZap » Thu Oct 25, 2018 8:48 am

Hi All, This is an amazing forum, thankful to have it. I'm looking for - and not finding - general guidelines for AGM SOC. As we head into the winter months, I'm wondering the frequency with which to run my generator. I thought this would be easier to find - happy to be slapped upside the head and sent a link.

Question: With AGM batteries overnight going to usually no more than 80%, should I run my generator if they don't get back to 100%? On cloudy days, they sometimes only get back to 90-95%, I guess that in the winter this could go on for a few days before I get close to %50DOD and HAVE to run my generator.

Info:
Completely off grid (solar, septic, well)
830AH, 48V AGM Batteries, 58.8 bulk/absorb, 54.4 float, 3hr absorb
7.7kW 17% eff 24v Panels (probably going to add ~1.7kw more - it's sitting in my garage doing nothing...)
Asimuth 205 deg, panels at both 20 and 45 degree to sun in 98329
VFXR3648/Mate3s w/ Rapid Shutdown

Thank you for the advice.

Mike Curran
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Posts: 1785
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My RE system: Outback - Garage roof:
- 8 (2x4) Evergreen 180's into one FM80 (2007/2020 - replaced MX60)
- 6 (2×3) ALEO S79-300's into one FM80 (2017)
- 2 grid-tied GVFX3524's classic stacked for 120/240VAC (2007)
- 12 Surrette/Rolls 2V x 1766Ah (2007)
- Hub10.3, Mate3s, FNDC, RTS, OpticsRE. Tigo Energy ES maximizers on each PV module.

Westinghouse Solar - Barn roof: (2012)
- 30 (2x15) 235W panels with Enphase M215 microinverters, grid-tied

Outback Skybox - Barn roof: (2019)
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Enphase M215 microinverters, normally direct grid tied

All self-designed and self-installed
Location: Chagrin Falls, Ohio

Re: General AGM Battery SOC/Overnight Guidelines

Post by Mike Curran » Thu Oct 25, 2018 10:05 am

I'm guessing your SOC numbers are coming from a FlexnetDC or similar device, which bases SOC on comparing current flows in vs. current flow out, or more likely (current in) ├À charge factor vs. (current out). Without specific gravity measurements to back up these type of SOC measurements, they are not the best way to judge SOC.

Rolls Battery has a section on operation and maintenance of AGM batteries in their battery manual, which basically uses battery voltage to judge whether an AGM battery is fully charged. Check it out, especially pages 24-27: http://rollsbattery.com/wp-content/uplo ... Manual.pdf
http://www.tigoenergy.com/site.php?95b2dca2-ca6c
https://enlighten.enphaseenergy.com/public/systems/Hctc107221

JPSolarZap
Forum Member
Posts: 13
Joined: Tue Feb 27, 2018 10:06 pm
My RE system: 7800w of array, flexpower 2 vfxr3648, 16 6v AGM 400ah

Re: General AGM Battery SOC/Overnight Guidelines

Post by JPSolarZap » Thu Oct 25, 2018 10:54 am

Thanks Mike for the response. I will look through the manual. Are there more absolute measurement "set it and forget it" devices you (or anyone) is aware of I can use to continuously monitor in better ways that the FlexNet that I have built in? I really value the online monitoring component of OpticsRE.

My batteries are Fullriver (16 ds400's). I assume the chemistry is the same as those rolls AGMs.

blackswan555
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My RE system: Other peoples, VFX "E" versions, FLA`s, Generators.
Location: Ibiza Spain,

Re: General AGM Battery SOC/Overnight Guidelines

Post by blackswan555 » Thu Oct 25, 2018 11:07 am

Are there more absolute measurement "set it and forget it" devices you (or anyone) is aware of I can use to continuously monitor in better ways that the FlexNet that I have built in?
Sadly no, The FNDC is one of the better ones but no battery monitor takes into consideration all on the variables that there are in battery charge, Discharge cycle, Have a look at https://en.wikipedia.org/wiki/Peukert%27s_law,
Bit like " I put 40l of petrol in my car, how far will it take me" without knowing what car, how fast you drive, load, traffic, temperature, etc etc,

Tim
My comments are based on my experience and research, They are not endorsed or checked by Outback.I am an independent British electrician living in Spain, So please take this into account when reading /acting on my post`s.

JPSolarZap
Forum Member
Posts: 13
Joined: Tue Feb 27, 2018 10:06 pm
My RE system: 7800w of array, flexpower 2 vfxr3648, 16 6v AGM 400ah

Re: General AGM Battery SOC/Overnight Guidelines

Post by JPSolarZap » Thu Oct 25, 2018 12:39 pm

Thanks Tim and Mike - for the good of the forum, I thought I'd extract this out of the Rolls AGM Battery charging section of the PDF Mike sent:
VRLA CHARGING GUIDELINES
To maintain good health, VRLA battries should be brought to a full charge on
each cycle or, at minimum, once every 6-7 days. Charge should be completed
in a ventilated area as gasses may be released through the pressure relief
valve if the batteries are excessively over-charged. Never charge a frozen
battery. Ideal charging temperatures: 0┬░C-40┬░C (32┬░F-104┬░F).


There's also a bunch of other great stuff in there on his referenced pages.

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