New 24 volt system AGM question

topper Solar Expert Posts: 113 ✭✭
I recently acquired a used XW4024, midnite E-panel, and a set of 12 Enersys Powersafe 12v155f's(4 year old batteries in excellent condition). For the price I couldn't back away being a beginner and all. $6.00 per battery and $900 for the inverter, Dist. panel, controller, battery rack,and wiring. If I screw up, I spent more in fuel and time then parts.
The batteries are set up in 6 strings @ 155ahr per string for a total of 930 ahr @ 24 volts. I know less strings are better, but dirt cheap is good too.

I have all the specs programmed as far as charger rates, voltages etc. That much I'm OK with.

My AGM question is: Looking at the enersys performance spec sheet, They list capacities down to 1.60Vpc=9.6 Volts per battery=19.2 volts in my 24 volt system.
These would have to be voltages under load, Correct?
Cause if not, These batteries would be very very dead and ready for the crap yard after 1 or 2 deep discharges.



  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: New 24 volt system AGM question

    that's taking them quite far down in any case, but i think it is a loaded voltage.
  • topper
    topper Solar Expert Posts: 113 ✭✭
    Re: New 24 volt system AGM question

    Discharge Rates in Amperes to 1.60Vpc at 25°C/77°F
    Minutes Hours
    TYPE 5 10 15 20 25 30 35 40 45 50 55 1 1.5 2 2.5 3 4 5 6 7 8 9 10 12 24
    12V155FS 498.0 352.8 280.6 239.7 210.1 186.3 167.7 152.1 139.3 128.6 122.0 109.7 79.7 63.2 52.5 45.1 35.4 29.3 25.1 22.0 19.7 17.6 16.1 13.6 7.25

    Cut n Paste didn't worjk so well. Sorry.
  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: New 24 volt system AGM question

    there should be a whole set like that are starting at ~ 1.9VPC down to ~ 1.60VPC. they are meant for doing load (depletion) tests... you don't want to go there unless you are willing to lose the set if it is failing, read their manual about periodic tests.

    Good catch
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • BB.
    BB. Super Moderators, Administrators Posts: 33,479 admin
    Re: New 24 volt system AGM question

    At least 20 years ago when I was designing equipment for Telephone Company use--They wanted good quality product-But expected it to run to destruction in an emergency situation.

    We had many arguments about if our system should down down >55C (131 F) or keep running (phone guys told us to keep running--we decided to shut down).

    Eventually, one of our systems had an electrical fire (capacitor failed shorted). System did shut down (fire was right under our temp sensor). Fire department came, broke through (very expensive) fire/security doors at the unattended central office, and found our system had shut down and stopped burning long before.

    In the end, that battery specification is, probably, an emergency operational specification (discharge to destruction is OK).

    In general, discharging below 11.5 volts (23 volts for 24 volt system) is probably about as low as you would like to go in normal operation (perhaps a few second to few minute time delay to allow surge current). Going to 10.5 volt (21 volt) is pretty much going to shorten the life of a new battery bank, and probably will kill a battery bank with more than a couple of years of service.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • topper
    topper Solar Expert Posts: 113 ✭✭
    Re: New 24 volt system AGM question

    Thanks for your interpretations.
    I think I'll leave the low batt cut out at 22.5-23 volts. I wouldn't mind this set lasting me at least a few years. I'm running as a UPS/backup power only till I get solared up.
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: New 24 volt system AGM question

    Once you discharge a bank really deeply, you end us "reverse charging" the lowest capacity cell in the system.

    When that happens, the battery (however many cells in the case, 1,3, or 6) is killed, and you have to replace it,
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    gen: ,

  • topper
    topper Solar Expert Posts: 113 ✭✭
    Re: New 24 volt system AGM question

    Well. I am very happy with my purchase. We have had some wicked weather June 26th, June 28th and July 1st. 2 4-6 hr outages and a couple brown outs for an hour or so due to high winds, hail and twisters.
    Batteries performed extremely well. Inverter worked and the wife didn't even know the power went out.(except for the digital clock on the stove).
    Thank-you to you all.