Charge rate, is faster better?

machinemanmachineman Solar Expert Posts: 129 ✭✭✭
First off, here's my off-grid cabin system: Magnum 4024 AE Inverter/charger, XW60 MPPT, 440Ah at 24V flooded batterys, 820watts of panels. Sometimes when I get down to 50% battery I turn on my 8Kw generator to boost them up. On the magnum inverter/charger I set the max charge rate to 80% and the shore(generator) current to pull 30amps. At this setting the charger pushes ~90amps into the batterys in bulk mode. Is this OK or is that to much to fast? Or can I set it to 100% charge rate and do it faster?

Thanks...

Off Grid Cabin, 24V 440ah 6V GC battery bank, Xantrex MPPT60-150 CC, Magnum MS4024 inverter-charger, >1200w Solar bank

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Charge rate, is faster better?

    Do not exceed a C/8 charge rate: 13% of the Amp hour rating of the batteries.
    Very high charge rates cause excessive heating of the plates, which can warp and distort them to the point of failure. In addition, the higher rate will 'boil off' more water and you run the additional risk of exposing the plates.

    You really shouldn't exceed 44 Amps charge rate on a 440 Amp hour bank.
  • mike95490mike95490 Solar Expert Posts: 8,497 ✭✭✭✭✭
    Re: Charge rate, is faster better?

    well, if the batteries are not gassing too much, and not heating, you might be able to go past the C/8 rate somewhat, but once they come up on bulk, they will start gassing and heating, and it can happen fast.
    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

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • machinemanmachineman Solar Expert Posts: 129 ✭✭✭
    Re: Charge rate, is faster better?

    I've done this about 5 or 6 times and running about 30min each time. Hope I didn't mess up the batterys. The water level is OK, I've only added once in 6 months.

    Off Grid Cabin, 24V 440ah 6V GC battery bank, Xantrex MPPT60-150 CC, Magnum MS4024 inverter-charger, >1200w Solar bank

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Charge rate, is faster better?

    Back it down to where the maximum current to the batteries is at 13% - 57 Amps. Really, even at 50% SOC it shouldn't take more than 5-6 hours to recharge. But habitually running the rate at 2X the recommended is bound to damage something sooner or later.
  • RCinFLARCinFLA Solar Expert Posts: 1,280 ✭✭✭
    Re: Charge rate, is faster better?

    When battery is discharged to 50%, you are okay at 25% C charge rate. Charging is very efficient when battery is less then 85% SOC.

    Current should drop quickly once absorb voltage is achieved.

    If you have batteries in more then one series string just make sure parallel groups don't end up greater then 25%. It is common to have some unbalance in parallel strings.

    When running from generator you want to load generator to at least 50-70% capacity to get best fuel efficiency.
  • Dave AngeliniDave Angelini Solar Expert Posts: 4,862 ✭✭✭✭✭
    Re: Charge rate, is faster better?
    machineman wrote: »
    First off, here's my off-grid cabin system: Magnum 4024 AE Inverter/charger, XW60 MPPT, 440Ah at 24V flooded batterys, 820watts of panels. Sometimes when I get down to 50% battery I turn on my 8Kw generator to boost them up. On the magnum inverter/charger I set the max charge rate to 80% and the shore(generator) current to pull 30amps. At this setting the charger pushes ~90amps into the batterys in bulk mode. Is this OK or is that to much to fast? Or can I set it to 100% charge rate and do it faster?

    Thanks...

    If you want the batteries to last a long time, if you know that the 20 hour rate is 440 AH, then current limit the charge rate to a maximum of 10% or 44adc if they are 440AH. 13 amps AC max seems about right.

    It is either lifting/buying extra fuel or replacing batteries, your call!
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Charge rate, is faster better?

    the 13% upper limit was really a factor set by trojan and some generic batteries. many quality batteries out there can take 20% or even as much as 30%, but don't assume yours can if you don't know. even at the 13% level it is a bit more maintenance involved over time, but nearly all batteries should be fine at the 13% rate. this will stir the electrolyte better than say 5% or 6%. 90a is over a 20% charge rate and may do harm unless the manufacturer gives the ok. the 13% rate for 440ah is 57.2a. 10% is a good level to be at for a lead acid battery as it is a good compromise to gassing, stirring electrolytes when applicable, speed of charge, and probably a few more points that i'm not thinking of right now, but the world isn't ideal and circumstances can differ to move off of that ideal at times.
  • BB.BB. Super Moderators, Administrators Posts: 29,812 admin
    Re: Charge rate, is faster better?

    Also, more than ~13% of solar panel charge rate is Expensive for panels and charge controllers. And does not do much for you unless you (batteries will not take all of the available energy once they are 80-90% charged) have something that can take much of the power during the day...

    For example, when the charge controller hits "Float"--You could automatically (or manually) turn on a water pump and fill your cistern/irrigate your land.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • zeuspaulzeuspaul Solar Expert Posts: 59 ✭✭✭✭
    Re: Charge rate, is faster better?
    For example, when the charge controller hits "Float"--You could automatically (or manually) turn on a water pump and fill your cistern/irrigate your land.

    How would you automatically go about doing this? For example I would like to turn on an AC water feature pump to use excess power while the sun is shining and then turn it off at perhaps a 15 or 20 percent draw down of the battery.

    I was going to use a timer and an estimated pump run time.

    Thanks

    Zeuspaul
  • BB.BB. Super Moderators, Administrators Posts: 29,812 admin
    Re: Charge rate, is faster better?

    I believe Outback FM/FX series charge controllers have a programmable (digital) output that can be configured to turn on when the controller is in float.

    There may be other controllers that have similar options.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Dave AngeliniDave Angelini Solar Expert Posts: 4,862 ✭✭✭✭✭
    Re: Charge rate, is faster better?
    BB. wrote: »
    Also, more than ~13% of solar panel charge rate is Expensive for panels and charge controllers. And does not do much for you unless you (batteries will not take all of the available energy once they are 80-90% charged) have something that can take much of the power during the day...

    For example, when the charge controller hits "Float"--You could automatically (or manually) turn on a water pump and fill your cistern/irrigate your land.

    -Bill

    Bill,
    And I am with you on expensive except when offgrid and you get into non ideal solar weather. The cost then becomes running a genertor as oposed to having enough solar for most conditions in a location that supports it. Either way you are going to pay, so one might as well decide if it is BP solar or BP petroleum/gas/?

    To the OP, Keep in mind that batteries, most all of them, like to be charged/discharged slowly for longest life. The manufacturer really has a conflict of interest when they publish high charge rates. They really want you to exceed the warranty and then start getting ready to buy again. The 10 percent max charge for a liquid Surrette or Trojan/similar is a time tested number that goes back decades. If you look at old recomendations from either of those companies you will see that they are really not your new best friends.

    You easily can get 10 to 15 years or need new batteries in less than 5. Other factors like depth of discharge, maintenance all are part of it. You also may find that as you grow into your system, it may not be such a bad thing to replace them at 5 years with the idea that things may be unplannable now.
    Buenas Suerte!
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • machinemanmachineman Solar Expert Posts: 129 ✭✭✭
    Re: Charge rate, is faster better?
    BB. wrote: »
    Also, more than ~13% of solar panel charge rate is Expensive for panels and charge controllers. And does not do much for you unless you (batteries will not take all of the available energy once they are 80-90% charged) have something that can take much of the power during the day...

    For example, when the charge controller hits "Float"--You could automatically (or manually) turn on a water pump and fill your cistern/irrigate your land.

    -Bill

    I usaully chrage from 50% and shut off then gen charging when it gets to around 70%. I have my inverter low voltage cut off set to 23.4v or around 48% battery. The magnum inverter / charger has a setting for battery ah and the charge rate %. I would assume it usses the ah and charge rate inputs to deliver the correct charge amps? I think the charge rate % setting is in inciments of 5 or 10%.

    Off Grid Cabin, 24V 440ah 6V GC battery bank, Xantrex MPPT60-150 CC, Magnum MS4024 inverter-charger, >1200w Solar bank

  • RCinFLARCinFLA Solar Expert Posts: 1,280 ✭✭✭
    Re: Charge rate, is faster better?
    Bill,
    The 10 percent max charge for a liquid Surrette or Trojan/similar is a time tested number that goes back decades.
    Buenas Suerte!

    You you believe 10% C recharge rate is max. then you must also believe 10% C discharge rate is max.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Charge rate, is faster better?
    RCinFLA wrote: »
    You you believe 10% C recharge rate is max. then you must also believe 10% C discharge rate is max.

    Charge and discharge rates are not comparable. Charging is a sustained application of current; discharging is nearly always varied and intermittent.

    If you were to survey the off-gridders here you'd probably find that on average discharge rates don't come close to 10%. Since we try to avoid discharging the batteries more than 50% over 20 hours, this is pretty obvious. That's an average of 2.5% per hour.

    A few calculations based on my own system: average sustained discharge rate; 4%. Highest discharge rate: 15% (pump start-up). Highest sustained discharge rate; 11%. Not really a strain on 10%, is it?

    In general, if you want real-world info about off-grid systems ask the people who use them.

    And as always, everyone is free to completely disagree with me and/or disregard my advice. :D
  • Dave AngeliniDave Angelini Solar Expert Posts: 4,862 ✭✭✭✭✭
    Re: Charge rate, is faster better?

    The 10% charge rule really has little to do with what I believe. It is based on what I was told by Mr. Surrette in 1978. I am too old to try anything new with charging a battery that I live off of. ;)

    Hey Marc! winter is coming! We had the nastiest lightning storm Sunday night.
    I was worried about the ultimate discharge rate!
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • SlappySlappy Solar Expert Posts: 251 ✭✭✭✭✭✭
    Re: Charge rate, is faster better?
    Hey Marc! winter is coming! We had the nastiest lightning storm Sunday night.
    I was worried about the ultimate discharge rate!

    Hummmm, (concord Sun Xtender batts claim a 300% charge rate), well lets see, make note to thy self. build lighting rod, connect to battery bank, wait for storm ;)
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Charge rate, is faster better?
    The 10% charge rule really has little to do with what I believe. It is based on what I was told by Mr. Surrette in 1978. I am too old to try anything new with charging a battery that I live off of. ;)

    Hey Marc! winter is coming! We had the nastiest lightning storm Sunday night.
    I was worried about the ultimate discharge rate!

    We've already had the first snow fall - two days before Autumn began! :confused:

    And I should have mentioned that the "4%" rate is actually during the day, when the panels are producing so it isn't really a discharge. Also, at night with just the inverter & 'frige running it's more like <1% average.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Charge rate, is faster better?
    Slappy wrote: »
    Hummmm, (concord Sun Xtender batts claim a 300% charge rate), well lets see, make note to thy self. build lighting rod, connect to battery bank, wait for storm ;)

    Igor! :p

    (If you don't read Terry Pratchett you won't get this.)
  • icarusicarus Solar Expert Posts: 5,391 ✭✭✭✭
    Re: Charge rate, is faster better?
    We've already had the first snow fall - two days before Autumn began! :confused:

    And I should have mentioned that the "4%" rate is actually during the day, when the panels are producing so it isn't really a discharge. Also, at night with just the inverter & 'frige running it's more like <1% average.


    We on the other hand are having the same fall that was spring. Temps 20c, with over night lows about +4. We should be maybe +4 during the day and -4 at night! Beautiful fall days though, I'm sure we will pay the price.

    Tony
  • machinemanmachineman Solar Expert Posts: 129 ✭✭✭
    Re: Charge rate, is faster better?

    Update: So I set my Magnum inverter/charger to a rate of 40% which equals about 40amps. So this is <10% of my 440ah capacity (24v bank) and I assume a safe condition.

    It appears that the charge % rate setting on the Magnum is not calculated based on the battery capacity (which is another input value) but likely 10% of the chargers max capability which is around 105aDC. So when I had it set to 80% it charges around ~85adc and at setting 40% it charges around ~40adc.

    With winter coming and being cloudy I'm doing a lot of charging.

    Off Grid Cabin, 24V 440ah 6V GC battery bank, Xantrex MPPT60-150 CC, Magnum MS4024 inverter-charger, >1200w Solar bank

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