Care and feeding of a UPS-style backup battery bank

RandomJoeRandomJoe Solar Expert Posts: 472 ✭✭✭
For a few different reasons, I have pretty well decided to purchase an Outback inverter to add to my system. (Biggest being the 30% rebate on taxes from my previous purchases last year will pay for it! :cool: ) If I do that, my battery bank will go from being used / recharged each day (I'm pulling less than 10% per day, very rarely do I make it down to 80% SOC) to essentially staying fully charged all the time, as my loads will be switched to grid power whenever solar can't handle them directly. (Except in outages, of course.)

So is there anything I should do differently with the battery bank to maximize lifespan / health in this new configuration?

One thing I've seen suggested a few times is to exercise the bank periodically (monthly?) - easy enough, I can just kill line-in some evening and let the bank run critical loads until the sun comes up the next day. How far down should I take it when exercising? Is monthly sufficient?

I've heard float duty is best for battery life, but of course my experience with most floated batteries (computer UPSes, typically) suggests that may not always be the case. I've seen some thoroughly trashed batteries coming out of old UPSes, sometimes only a couple years old. But that may have more to do with the design of the UPS charging circuits, or how often the power dies and the batteries get fully drained... I just don't want to find I've abused my batteries after the fact!

Anything else to consider? Or am I worrying about nothing? :p

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Care and feeding of a UPS-style backup battery bank

    Do you already have an Outback charge controller? If so, get a Hub, Mate and cables to connect the inverter and controller. That way you program the 'inverter charging' to the same specs as the controller charging and both will read from one temp sensor. In that case, if the batteries are 'happy' with your existing settings they'll stay 'happy' even when charged from the grid because the settings will be identical - only the source changes.

    It can be done without the Hub (you need a Mate to alter the inverter's programming) but it's a pain and it won't share RTS input.
  • BB.BB. Super Moderators, Administrators Posts: 29,713 admin
    Re: Care and feeding of a UPS-style backup battery bank

    I would suspect that the "cheap UPS's" don't really float the battery but keep the voltage much closer to 14.2 volts vs closer to 13 volts--and there is probably no battery temperature compensation.

    Basically they just "cook" the batteries on standby. I failures I have seen, just don't make sense if the systems really where correctly floating the batteries.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • RandomJoeRandomJoe Solar Expert Posts: 472 ✭✭✭
    Re: Care and feeding of a UPS-style backup battery bank

    Coot: Actually, I already have the entire system *except* the OB inverter! :roll: The money I spent on my other inverters would have paid for the OB in the first place, but well...

    My goal is to maximize production from the panels / minimize utility usage, so I may even try having the inverter NOT charge the batteries until they are a certain amount discharged. (I don't have enough continuous loads to max out the solar panels by themselves, and don't want to go grid-tie at this point...) I think the OB has some settings for that sort of operation...


    BB: That's a definite possibility. Most of the UPSes I've seen were the smaller, cheaper ones. I currently have a couple of larger "server" ones that I replaced the batteries in (they were 5 years old and headed to the trash can!) and those were in considerably better shape. Primarily just a lot of corrosion on the terminals. Now I think of it, I got those from my last employer so the batteries I have in them now are at least four years old and still hold up okay when testing!

    I've also seen some batteries come out bulging, on a couple of occasions. Mostly just completely dead after only a year or two! And always corroded terminals - which struck me as odd, since they are AGMs... I've never had any of my AGMs get corrosion on the terminals!
  • BB.BB. Super Moderators, Administrators Posts: 29,713 admin
    Re: Care and feeding of a UPS-style backup battery bank

    Sounds like Over Charging... Excessive Oxygen on the positive grid from over charging (electrolysis). Causes cases to bulge and "positive posts" rise (and leak?).

    Also, the catalyst is eventually eroded by hydrogen/oxygen recombination... Over charging can over heat and cause early catalyst failures too (as I read around here and there).

    There is a thread around here about "rejuvenating" AGM batteries by adding new caps with catalyst and even adding a bit of water to the cell.

    As long as you don't have the positive plate corrosion (post elevation, bulging of cell walls)--sounds interesting to try (although to do the watering correctly--It sounds like you need to set up test gear to accurately measure cell impedance to get the water percentage correct).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • blackswan555blackswan555 Solar Expert Posts: 246 ✭✭
    Re: Care and feeding of a UPS-style backup battery bank

    Are you going to install a FNDC ? May be a good idea for your batteries, It has a "charge to full" setting that may be of use to you,
    As for your bat life ( what type of bat`s ? ) With an only occasional 20% DOD and looked after they should last for years anyway.
    Have a good one
    Tim
  • RandomJoeRandomJoe Solar Expert Posts: 472 ✭✭✭
    Re: Care and feeding of a UPS-style backup battery bank

    I already have the FNDC. Currently I have an FM80, FNDC and Mate tied together with a 10-port hub! Plenty of room for expansion... :p

    Spent some time reading through the manuals yesterday, and it does look like I should be able to do almost anything I want (a few things I may have to do myself, based on data retrieved from the Mate) but that's just part of the fun for me! :D

    I was a bit disappointed to see that (apparently) the Mate will use the FNDC data to enhance its decision when to start/stop a generator, but when deciding whether to go grid or not it just has bank voltage setpoints... May just have to "pretend" my grid connection is a generator! Gotta think more on that...

    My thought at this point is to make sure I keep the panels producing maximally during the day by using a bit of battery power overnight - or more likely in the morning just before dawn, spend as little time discharged as possible. I don't have enough continuous daytime loads to do that, and I'm not grid-tied so can't just push it that way. I do, however, have a couple of servers that stay on 24x7 and could handily contribute to some load-shifting overnight. But voltage settings really aren't anywhere near accurate enough. With the FNDC I can "count AH" and use that as a basis for when to switch.

    At this point the whole project has become more of a fun hobby / experiment for me! 8)
  • blackswan555blackswan555 Solar Expert Posts: 246 ✭✭
    Re: Care and feeding of a UPS-style backup battery bank
    May just have to "pretend" my grid connection is a generator! Gotta think more on that...

    You could do that using a contactor switched from the AUX (be a little careful, the FX aux is only 800ma @ 12v, You may want to use a relay > contactor coils) to fool it into thinking it`s a gen,beware if you have grid fail during "charging" It will throw an AGS error,
    Let FNDC control charge, Set SOC start to your desired level, End of charge parameters for stop (amp/V/Time) set return to full charge to what you like, Then aim for the panels to keep it in limbo between those settings, If they do not , grid kicks in and gives a full charge, If they do, bat`s get a full charge whenever, If they are FLA`s, discharge to 40% SOC recharge and EQ every 1 > 3 months depending on SG readings,

    Have a good one
    Tim

    ps, You may want to check your mate firmware, You need the latest for all FNDC & FM functions, It`s a free upgrade from OB
  • RandomJoeRandomJoe Solar Expert Posts: 472 ✭✭✭
    Re: Care and feeding of a UPS-style backup battery bank

    Yeah, that's an idea. Thanks!

    How "new" is the latest firmware? I'll have to check when I get home, I bought my Mate last spring. IIRC it had the "latest" at that point in time anyway...

    I have to say, I'm a bit gun-shy of getting it updated... I had a less-than-happy experience with Outback when I had to get the FNDC updated. Not real keen on repeating that...

    Edit: Okay, I see I'm a couple minor revisions behind on the Mate. I have version 4.1.4. Not sure if getting up to 4.1.6 will gain me much of interest yet.
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