What is the maximum current for my absorb cycle

Shawn-HShawn-H Solar Expert Posts: 107 ✭✭
I have 8 6 volt Rolls s-480 batteries on a 24V FW500 system for a total of 750AH/20hr. My 6hr is 275*2, and my 20hr is 375*2. What is the maximum number of amps I should send to those batteries. I'm coming up with 75A max but need to be sure.
100% Off-grid in the White Mountains of Arizona. 36 Kyocera 265w mounted on four DPW 9 module pole top mounts, midnite solar combiners, breakers, & lightning arresters, 1 midnight solar classic 150, & 3 classic 150 lights, 3 x 1574 AH GB Industries forklift batteries total of 4722 AH @24v. Feeding a Outback power systems FW500 with 2 x VFX 3624, with the x240. 2 Honda EU3000is gensets with the 240 combiner and control box running LP, and 1 Honda EU2000is Gas. 
System #2 is a off grid water system @ 1590w (6 Kyocera 265's) on a 6 module DPW top of pole mount. Feeding a Granfas deep well pump and pump controller at 580 feet. 2 x 2800 gallon above ground poly storage tanks, and 1 x 1200 gallon underground  cistern and a Granfas 24v booster pump feeding a 90 gallon carbon fiber pressure tank.
Vag woodstove for heat.
Follow our journey at
https://www.facebook.com/ShawnpHarvey

Comments

  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    A good rule of thumb is 10% of the 20 hr ah capacity. It's OK to go a bit higher, and depending on your consumption you may get away with half of that. Remember that the higher the charge rate, the less efficient the charging is and the more heat is created in the batteries.

    In the winter I often charge at 13% (with generator) because I want to heat up the batteries a bit. In the summer, I would rather charge slower, and the days are longer so I can get away with charging slower.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • Shawn-HShawn-H Solar Expert Posts: 107 ✭✭
    vtmaps wrote: »
    A good rule of thumb is 10% of the 20 hr ah capacity. It's OK to go a bit higher, and depending on your consumption you may get away with half of that. Remember that the higher the charge rate, the less efficient the charging is and the more heat is created in the batteries.

    In the winter I often charge at 13% (with generator) because I want to heat up the batteries a bit. In the summer, I would rather charge slower, and the days are longer so I can get away with charging slower.

    --vtMaps

    Thank you so it sounds like I'm right on
    100% Off-grid in the White Mountains of Arizona. 36 Kyocera 265w mounted on four DPW 9 module pole top mounts, midnite solar combiners, breakers, & lightning arresters, 1 midnight solar classic 150, & 3 classic 150 lights, 3 x 1574 AH GB Industries forklift batteries total of 4722 AH @24v. Feeding a Outback power systems FW500 with 2 x VFX 3624, with the x240. 2 Honda EU3000is gensets with the 240 combiner and control box running LP, and 1 Honda EU2000is Gas. 
    System #2 is a off grid water system @ 1590w (6 Kyocera 265's) on a 6 module DPW top of pole mount. Feeding a Granfas deep well pump and pump controller at 580 feet. 2 x 2800 gallon above ground poly storage tanks, and 1 x 1200 gallon underground  cistern and a Granfas 24v booster pump feeding a 90 gallon carbon fiber pressure tank.
    Vag woodstove for heat.
    Follow our journey at
    https://www.facebook.com/ShawnpHarvey
  • PhotowhitPhotowhit Solar Expert Posts: 4,996 ✭✭✭✭
    Check with Rolls info, I believe 13% maybe 15%, I have my classic lites set so they shouldn't send more than 15% to my forklift battery. It's a rare day when they could. I don't think boB has the Whiz Bang software setup so it can limit based on what is going into the battery, but I haven't checked this year. That would be the idea way.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
  • Shawn-HShawn-H Solar Expert Posts: 107 ✭✭
    Photowhit wrote: »
    Check with Rolls info, I believe 13% maybe 15%, I have my classic lites set so they shouldn't send more than 15% to my forklift battery. It's a rare day when they could. I don't think boB has the Whiz Bang software setup so it can limit based on what is going into the battery, but I haven't checked this year. That would be the idea way.

    Thank you photowhit. It's actually 15% of the 6 hour rate which comes out to a really low number they mention later in the literature to use 10% of the 20 hour rate this is why I'm asking it's where all the confusion is coming from for me
    100% Off-grid in the White Mountains of Arizona. 36 Kyocera 265w mounted on four DPW 9 module pole top mounts, midnite solar combiners, breakers, & lightning arresters, 1 midnight solar classic 150, & 3 classic 150 lights, 3 x 1574 AH GB Industries forklift batteries total of 4722 AH @24v. Feeding a Outback power systems FW500 with 2 x VFX 3624, with the x240. 2 Honda EU3000is gensets with the 240 combiner and control box running LP, and 1 Honda EU2000is Gas. 
    System #2 is a off grid water system @ 1590w (6 Kyocera 265's) on a 6 module DPW top of pole mount. Feeding a Granfas deep well pump and pump controller at 580 feet. 2 x 2800 gallon above ground poly storage tanks, and 1 x 1200 gallon underground  cistern and a Granfas 24v booster pump feeding a 90 gallon carbon fiber pressure tank.
    Vag woodstove for heat.
    Follow our journey at
    https://www.facebook.com/ShawnpHarvey
  • ApplesApples Solar Expert Posts: 39 ✭✭
    Too, max current should be only a concern during the charge cycle's "bulk" phase, before absorption (bulk up to about 80% SoC). "Absorption" phase charging should be voltage-dominated, and in the high 14s, not 14.4, as so many will prescribe. 14.8 volts is desirable for absorption, 14.7 V if using AGM batteries. Absorption-phase charging, using 14.7 or 14.8 volts, should be for several hours, with only limited current.

    I may be behind the curve by saying this, but the only safe way to charge in this manner is with a microprocessor-controlled charger/charge controller.
  • VicVic Solar Expert Posts: 2,970 ✭✭✭✭
    Apples wrote: »
    ... "Absorption" phase charging should be voltage-dominated, and in the high 14s, not 14.4, as so many will prescribe. 14.8 volts is desirable for absorption, 14.7 V if using AGM batteries. Absorption-phase charging, using 14.7 or 14.8 volts, should be for several hours, with only limited current.

    Speaking only about Flooded Surrettes, Surrette recommends 14.4 Vabs (per 12 V) nominal at 25 degrees F. This is 28.8 for Shawn-H's batteries -- Temperature Compensated. During Winter months, when days are short, and weather often inclement, then, increasing Vabs above what is recommended is often needed to get as much battery charging done, as possible with limited sun.

    Also, if batteries are not getting charged well, and SGs are lagging, then it can be OK to increase Vabs to get SGs back to where they need to be.

    None of the Surrette banks here have ever needed more than 58.4 Vabs (14.6/12V) (29.2 for 24 V), and that is on occasion in the Winter. Usually run at about 58 Vabs at other times +/-- 0.1 V. (all temp compensated).

    The above related more to the SG of the electrolyte used. Most Surrette Flooded RE batteries use 1.265 SG electrolyte, and this is one of the main reasons that high Vabs settings are not needed. Batteries with 1.277 - 1.280, and higher do usually need a bit higher Vabs.

    Really, using SG readings as a guide, one needs to set absorption voltage and time. Absorb time depends upon DOD, and Vabs. Using battery Finishing Current -- End Amps is a very good to terminate Absorb, especially on batteries that have variable DODs from one day, to the next.

    Just my opinions. Vic


    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • ApplesApples Solar Expert Posts: 39 ✭✭

    Thanks, Vic!

    My limited experience comes from my use of AGM batteries and of one brand in particular which likes as much current as you could send it (far more than the current generated from photovoltaics) during bulk-phase charging but then a high voltage setting during absorption. My book-learned experience with flooded batteries in a solar battery bank comes from a man who has repaired and made work poorly-installed "factory" solar RV systems.

    Bottom line is, learn about the battery brand you've chosen to use. Talk to it's manufacturer's tech dept about how that battery likes to be charged then be sure you're using the necessary wire sizes to connect everything together.
  • PhotowhitPhotowhit Solar Expert Posts: 4,996 ✭✭✭✭
    Of course even Battery tech depts. can't get on the same page sometimes! As I've pointed out a couple times Trojan specifically says not to equalize unless they batteries SGs differ by more than a certain amount... But they have a Youtube video out that says equalizing is the secret to long battery life...

    I think Rolls suggests evry month for some of their batteries and every 6 months for others...
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
  • Shawn-HShawn-H Solar Expert Posts: 107 ✭✭
    Thank you all. With out you guys I would have never maid the leep to offgrid.
    100% Off-grid in the White Mountains of Arizona. 36 Kyocera 265w mounted on four DPW 9 module pole top mounts, midnite solar combiners, breakers, & lightning arresters, 1 midnight solar classic 150, & 3 classic 150 lights, 3 x 1574 AH GB Industries forklift batteries total of 4722 AH @24v. Feeding a Outback power systems FW500 with 2 x VFX 3624, with the x240. 2 Honda EU3000is gensets with the 240 combiner and control box running LP, and 1 Honda EU2000is Gas. 
    System #2 is a off grid water system @ 1590w (6 Kyocera 265's) on a 6 module DPW top of pole mount. Feeding a Granfas deep well pump and pump controller at 580 feet. 2 x 2800 gallon above ground poly storage tanks, and 1 x 1200 gallon underground  cistern and a Granfas 24v booster pump feeding a 90 gallon carbon fiber pressure tank.
    Vag woodstove for heat.
    Follow our journey at
    https://www.facebook.com/ShawnpHarvey
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