Using UPS Batteries

Copperking
Copperking Registered Users Posts: 17
OK--as always thanks to this Forum. Got my Bld Permit and as the weather allows getting it done.
Ran accross a large data room UPS with all new Batts. This system is all sealed UB12180 batterys, 12v, 18ah, --51 total batts in 3 cabinets of 18, 18, and 15 (the guy used 3 for his motorcycles). I can't test sg but the voltage looks good. When/if I decide to use this system for a short time --couple years--I would have 4 batts in series and 12 parallel strings. Everything I have read says keep the parellel strings to a minimum. Presently the batts are wired with 14awg. Some of the wire could still be used but it seems the best way to parellel this system would be a buss bar. This should equalize the charge for so many batts better.
Now my system is grid tied and the battery backup is as much for the Outback FP 1-4 which requires batteries as it is for the few times the juice fails from the local co-op. So really once charged these batts should be on trickle at least until I finish my phase one solar install and go onto phase 2 which will require real batts to take the house off grid. Oh --don't tell the Wife there is a phase 2.
So what do you think? Am I wasting my time and I should just recycle this system?

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Using UPS Batteries

    Actually, smaller gauge cabling sort of helps paralleling batteries. The additional resistance will keep the current a bit better balanced (the resistance of the wiring will be higher than the battery resistance). You can double check the expected amperage discharging/charging and make sure the wiring is heavy enough that it does not overheat.

    You should probably research/measure DC current into the UPS system at light/no loads and make sure that you don't end up with a large portion of your solar power just ticking over the UPS (standard UPS systems are not always the most efficient devices out there--they assume grid power/backup generators).

    I am not sure how long your batteries will last--Most UPS systems are designed to run at highe for 30 minutes and take the batteries pretty flat (emergency use, not daily use). So UPS batteries seem to last just a couple years between replacements. Also, the battery bank AH capacity is usually a lot smaller than we would normally design for an off grid system (lower peak power at many hours per day).

    These batteries appear to be AGM--But the charging current is limited to a maximum of C/5:
    [SIZE=-1]Cycle Applications: Limit initial current to 3600mA. Charge until battery voltage (under charge) reaches 14.40 to 14.70 volts at 68oF (20[/SIZE][SIZE=-1]o[/SIZE][SIZE=-1]C). Hold at 14.40 to 14.70 volts until current drops to approximately 180mA. Battery is fully charged under these conditions, and charger should either be disconnected or switched to "float" voltage.

    "Float" or "Stand-by Service": Hold battery across constant voltage source of 13.50 to 13.80 volts continuously. When held at this voltage, the battery will seek its own current level and maintain itself in a fully charged condition. [/SIZE]

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Copperking
    Copperking Registered Users Posts: 17
    Re: Using UPS Batteries

    A clarification---the only thing I am going to use would be the cabinets and the batteries. The electronic and controller part of this UPS is in an additional smaller 4 cabinets that contain another 20 small 5ah hour batts. I was thinking of just selling that intact.

    Bill - when you post of charge rates, is that each batt or the whole bank? What would you use to charge with? Just set the rate in the FM80 or do you have a pretty fancy charger? I may well need such a charger since I have extra batts for the system. And no I don't intend to use this batt system as an end all. But at the moment the batts are here and the price is right. Everytime I go to the orange or blue big box store at this stage of my installation 100s disappear.

    That is interesting on the wire guage, i have a lot of 10awg I may use for the parallel connections to the Buss.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Using UPS Batteries
    Copperking wrote: »
    A clarification---the only thing I am going to use would be the cabinets and the batteries. The electronic and controller part of this UPS is in an additional smaller 4 cabinets that contain another 20 small 5ah hour batts. I was thinking of just selling that intact.

    For a "true off grid system"--I would not use batteries that are so small--I like large cells which could be from 100 AH to 1,000 AH or more. Basically, I am probably the big proponent here of reducing the numbers of paralleled battery strings to ONE... Possibly 2 to 3 maximum parallel battery strings based on a specific install and what batteries are available locally.

    My reasons are many--But break down into a couple of groups:

    Costs--There are more wiring (and should be a fuse/breaker per series string) to prevent short circuits in one string from being fried by the other parallel strings. "Big" wiring and fusing/breakers are not cheap.

    Maintenance--If flooded cell, more cells to check electrolyte levels in... 3 parallel strings, 3x as many cells to check. Also, it becomes more difficult to monitor for "bad cells" (shorted/open) and poor electrical connections to ensure that everything is working well. If you are up for the maintenance, there are now "cheap" DC Current Clamp Meters which make checking current sharing (under heavy loads and heavy charging) much easier... Such as this "good enough" $60 unit from Sears (is actually a decent DMM--digital multi meter too). I would suggest once a week to once a month to check current flow, and individual cell voltages (or battery block voltages) under different conditions (charging/discharging/no current flow). It should be pretty quick--you are looking for "differences"... If there is one reading that is quite low or quite high--Then investigate further.

    Reliability--This is a tough one... You can argue that parallel strings let you pull a string if there is a problem with a failed battery. On the other hand, with 2 or more parallel strings, you have 2 or more chances for things to go wrong. Single string systems generally are more "obvious" when there is a failure somewhere, it is easy to see just with a quick glance at the bank voltage. With paralleled strings, an open/shorted cell (or open wiring) is not so obvious, and if you don't do the weekly/monthly maintenance checks (above), a "hidden" failure can take out an entire string or bank.

    In the end, there are lots of people that are very happy with more than 3 parallel strings of batteries and they get long life out of their banks. Just my two cents on why I would try to avoid paralleling as much as possible.
    Bill - when you post of charge rates, is that each batt or the whole bank? What would you use to charge with? Just set the rate in the FM80 or do you have a pretty fancy charger? I may well need such a charger since I have extra batts for the system. And no I don't intend to use this batt system as an end all. But at the moment the batts are here and the price is right. Every time I go to the orange or blue big box store at this stage of my installation 100s disappear.

    It is Amps per Battery or Batteries series string (volts add when you connect batteries in series).

    For a bank, it is times the number of parallel strings (amps add when batteries/battery strings are connected in parallel).

    Numbers for solar are pretty "soft"... The batteries will not be "happy" at 20% and die at 25% rate of charge. However, at over ~C/8 (12.5%) rates of charge (normally a rate point for flooded cell batteries, AGM can take higher rates of charge in general), and especially if batteries are deeply discharged, then thermal management becomes more important as the batteries can overheat with high rates of charging current (and/or high voltage charging when over ~80-90% state of charge--more charging current is turned into hydrogen/oxygen gases and into heat). If you have "day time" loads (i.e., water pumping), those will reduce current flow into the battery bank, so programming a limit on the charge controller can be counter productive (need that new option to measure current flow into battery bank, not just out of charge controller).

    If you have a very large solar array, you could program the FM80 to reduce charging currents--But I probably would only do that if you see >20% rates of charge for sustained hours and/or dramatically over 20% (say 25-40% or more). I would recommend using a Remote Battery Temperature Sensor on the battery bank if a) you have high rates of charge current available, b) the batteries have a wide swing in temperature due to climate, or c) if the charge controller is in a different room/space than the battery bank (internal controller sensor reads different than back temperature).

    I keep going back to loads--Define your needs there first, then design the rest of the system. It is very easy to buy hardware then figure out that you don't have a good match--Or once you get the system fired up, it is over/under kill for your needs.

    A starting system, I would suggest golf cart batteries--They will last you ~3-5 years--And at that point, you can decide where to go next (bigger/smaller/better batteries, etc.).
    That is interesting on the wire gauge, i have a lot of 10awg I may use for the parallel connections to the Buss.

    The downside is more losses (I2R heating) and the fact that most UPS systems are designed to only run for 15-30 minutes or so at rated power--You starting running them for hours to days at a time--And you may find their thermal management issues to be a big problem (everything slowly cooks). Remember the equation for aging of 1/2 the life for every 10oC (18oF) increase in temperature applies to "everything"--Batteries, wiring insulation, corrosion, electronics, etc... If the unit "runs" hot, it will age faster--Plus thermal cycling can become an issue too (hot/cold/hot/cold cycling can pop components off of circuit boards, loosen electrical connections, etc.).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Copperking
    Copperking Registered Users Posts: 17
    Re: Using UPS Batteries

    Thanks BB
    No I know this is just a temp fix---but I got it for near free, and my attitude is that I can recycle it now or later if/when it fails.
    The long term plan is to get forklift batts and reduce the number of batts by a factor of 10.

    But --at the moment the system is going to be grid tied and whatever drain is placed on these UPS batts will be at a minimum once or twice a year.
    Your point on maintaining these is well taken and I believe I will start a baseline log on each series/parallel point as I set this up.
    Todays task is to get this dirt work/conduit task done before the next big snow.
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Using UPS Batteries
    Copperking wrote: »
    But --at the moment the system is going to be grid tied and whatever drain is placed on these UPS batts will be at a minimum once or twice a year.
    Your point on maintaining these is well taken and I believe I will start a baseline log on each series/parallel point as I set this up.
    Todays task is to get this dirt work/conduit task done before the next big snow.

    There is a very big difference between batteries designed for UPS or backup use and batteries designed for constant daily cycling of the type needed for truly off grid systems.
    If you are truly only going to rely on the batteries once or twice a year (plus occasional testing to a shallow discharge to make sure the system will work when you need it), then any kind of battery that can supply the peak power and the total energy that you need will be fine, even if in that service they are only good for 20 charge/discharge cycles. And recharging them quickly will not be an issue either.

    I would say that as long as the batteries you have are in good enough shape that their capacity meets your needs, you should go ahead with them. And plan to charge them with a float charger running off grid AC while your panels are connected only to the Grid Tie Inverter (GTI).
    SMA SB 3000, old BP panels.