What setting for battery charging from grid?

experimenter
experimenter Registered Users Posts: 20 ✭✭
I have 4 12V AGM Concorde 104AH batteries in series so they total 48v nominal. I also have a Morningstar MMPT charge controller. And, a Magnum MS4448PAE inverter. The inverter has a ME-ARC remote controller attached.

Using the remote, I can set the inverter to use grid power to charge the battery bank by voltage, state-of-charge, time of day, or auto. I want the solar cells to run the loads most times, until the batteries are discharged to 80% or so, then for the inverter to use grid power to charge the batteries back up to full.

Which of the above settings should I use? I've been using the voltage setting, with the grid disconnecting once the batteries reach 54.8 volts. But I don't want to overcharge the batteries.

Comments

  • PNjunction
    PNjunction Solar Expert Posts: 762 ✭✭✭
    Re: What setting for battery charging from grid?
    I have 4 12V AGM Concorde 104AH batteries in series so they total 48v nominal. I also have a Morningstar MMPT charge controller. And, a Magnum MS4448PAE inverter. The inverter has a ME-ARC remote controller attached.

    Has each been charged individually with a 12v charger to help ensure balance before you placed them into the 48v series string service? This is essential at least once!
    Using the remote, I can set the inverter to use grid power to charge the battery bank by voltage, state-of-charge, time of day, or auto. I want the solar cells to run the loads most times, until the batteries are discharged to 80% or so, then for the inverter to use grid power to charge the batteries back up to full.

    Ouch! That's the most expensive way to do it, as you'll be replacing those expensive batteries much sooner than usual driving them below 50% DOD. Another factor is will your loads actually *run well* at the terminal voltages presented when you are under 50% DOD, ie like 11.5v or so?

    One way to start is by obtaining the users manual here. Choose your specific battery line, and at the bottom of the page you'll find a pdf of the manual. Be sure to review this.

    http://www.concordebattery.com/
    or more specifically for Lifeline:
    http://www.lifelinebatteries.com/

    This isn't a cold rtfm reply since we don't know what your load requirements are, nor the output of your solar array. We'll need to know your geographical location to get a handle on your solar-insolation hours (they are not just sunrise-to-sunset). This information is necessary to make sure the system is able to take care of those great batteries.
  • AuricTech
    AuricTech Solar Expert Posts: 140 ✭✭
    Re: What setting for battery charging from grid?
    I have 4 12V AGM Concorde 104AH batteries in series so they total 48v nominal. I also have a Morningstar MMPT charge controller. And, a Magnum MS4448PAE inverter. The inverter has a ME-ARC remote controller attached.

    Using the remote, I can set the inverter to use grid power to charge the battery bank by voltage, state-of-charge, time of day, or auto. I want the solar cells to run the loads most times, until the batteries are discharged to 80% or so, then for the inverter to use grid power to charge the batteries back up to full.

    Which of the above settings should I use? I've been using the voltage setting, with the grid disconnecting once the batteries reach 54.8 volts. But I don't want to overcharge the batteries.

    It's very important for the life of your batteries that you clarify what you mean here, as your statement is quite ambiguous. Which do you mean: batteries discharged to 80% depth-of-discharge (very bad, as you've left them nearly dead by this point; even Miracle Max can only revive the mostly-dead so many times) or batteries discharged to 80% state-of-charge (a bit shallow, but workable)?
  • experimenter
    experimenter Registered Users Posts: 20 ✭✭
    Re: What setting for battery charging from grid?

    Sorry, I meant that I want to bring the batteries down to 80% of capacity before using grid power to recharge them fully. (batteries discharged to 80% state-of-charge)

    AuricTech wrote: »
    It's very important for the life of your batteries that you clarify what you mean here, as your statement is quite ambiguous. Which do you mean: batteries discharged to 80% depth-of-discharge (very bad, as you've left them nearly dead by this point; even Miracle Max can only revive the mostly-dead so many times) or batteries discharged to 80% state-of-charge (a bit shallow, but workable)?
  • experimenter
    experimenter Registered Users Posts: 20 ✭✭
    Re: What setting for battery charging from grid?
    PNjunction wrote: »
    Has each been charged individually with a 12v charger to help ensure balance before you placed them into the 48v series string service? This is essential at least once!

    No, this was not done.

    ...

    One way to start is by obtaining the users manual here. Choose your specific battery line, and at the bottom of the page you'll find a pdf of the manual. Be sure to review this.

    Believe me, I have read the manuals. But I am confused between the best way to use grid-connected power for recharging. The current panel set i have cannot keep the batteries charged (well, it can in the summer, but not in the winter). I am using battery voltage output now but hear that is not reliable because temp differences can change the voltage output. I have used SOC in the past but don't know how the inverter calculates that, so am not sure that is the best method. I could use AUTO, but not sure what the algorithm is behind that one either. Or i can just hook up the grid juice for a specific period of time each day.

    Which will maximize the life of the batteries?
  • Marc Kurth
    Marc Kurth Solar Expert Posts: 1,142 ✭✭✭✭
    Re: What setting for battery charging from grid?

    It would seem to me, that topping your batteries off using grid power, should occur after giving solar a shot at it. If solar alone was able to do the job, then the inverter/charger will see a full battery and go to float rather quickly. If the battery bank needs a charge, it will take care of it. Edit to add: So, maybe time of day - as long as you keep an eye on the depth of discharge.

    Maximum battery life will come with shallow cycling, always getting them back up to fully charged and a nice cool location.
    I always have more questions than answers. That's the nature of life.
  • experimenter
    experimenter Registered Users Posts: 20 ✭✭
    Re: What setting for battery charging from grid?

    I agree, solar should have first shot at recharging. But is that what the inverter or charge controller actually does? Does it "prioritize" solar over grid? Or is it programmed to say "Oh, there are 4 amps of current available from the solar panels and 30 amps form the grid, so grid will recharge the batteries faster, so I will use that"? The manuals don't explain this.

    Also, with both a Morningstar MMPT charge controller and the inverter's own charger in the circuit, which one actually controls charging?
  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: What setting for battery charging from grid?

    A thought, if you were off grid and using a gen set you would do the bulk with the gen as you get the best $ bang for the run time and let solar finish of the slow charge of Absorb and Float.

    With grid it is less of an issue.
     
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: What setting for battery charging from grid?
    I agree, solar should have first shot at recharging. But is that what the inverter or charge controller actually does? Does it "prioritize" solar over grid? Or is it programmed to say "Oh, there are 4 amps of current available from the solar panels and 30 amps form the grid, so grid will recharge the batteries faster, so I will use that"? The manuals don't explain this.

    Also, with both a Morningstar MMPT charge controller and the inverter's own charger in the circuit, which one actually controls charging?

    Without a very complex unit like an Outback FNDC or Xanbus system the controller and inverter do not share any info on battery charging. What happens, happens. The inverter (or charge controller) has no way of knowing anything about other charge sources except what it sees as battery Voltage. I expect the Magnum's SOC is based on current in/out through the inverter unless there is a separate external shunt measuring all current too/from the battery. Often these are used as battery-only back-up systems so other charge sources would not be taken into account.

    To give solar "first shot" at charging use a low Voltage as a trigger for the inverter-charger; if the solar can't keep it above that minimum the inverter-charger will do it (once charging starts it will continue until done). So long as the Absorb and Float Voltages are set equally the batteries will not over-charge. One issue may be length of Absorb time; if I recall correctly both the MS controller and Magnum inverter have 'fixed length' Absorb times with no End Amps function and no count-up/down timer.

    Usually when there is grid available solar will be used to charge only when grid goes down.

    Question: is there a battery RTS for the Magnum? That will compensate Voltage for temperature variations.
  • experimenter
    experimenter Registered Users Posts: 20 ✭✭
    Re: What setting for battery charging from grid?

    No gen in this setup, but I think if I did have a generator the question would be the same -- how to you set the inverter to prioritize gen power, panel power, or grid power?
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: What setting for battery charging from grid?
    No gen in this setup, but I think if I did have a generator the question would be the same -- how to you set the inverter to prioritize gen power, panel power, or grid power?

    You don't.
    Inverter has no way of knowing what the PV is doing unless there is a communication system like I mentioned.
    Inverter detects AC on input, it uses it regardless.
    With Automatic Generator Start circuitry you can program control of AC input to meet desired criteria. Depending on the system this can include mandatory run time, mandatory no-run time, regular use, Voltage start/stop, et cetera. The difference is with grid instead of the AGS starting a generator it engages a relay to connect the AC to the inverter's AC IN.

    Other than problems with running the inverter's charger at the same time as the PV is charging at full power (possibly 2X max current to batteries - not good) there's no reason the two charging systems can't operate together but independently. The batteries get charged just the same. BTW, the 2X current problem can be avoided with an AC activated relay disconnecting the PV from the controller so that any time the inverter is doing the charging the PV is not.
  • experimenter
    experimenter Registered Users Posts: 20 ✭✭
    Re: What setting for battery charging from grid?

    "Question: is there a battery RTS for the Magnum? That will compensate Voltage for temperature variations. "

    Yes, there is a temperature sensor at the battery bank location.

    And OK, I can set the minimum voltage as 49.0 volts or something close to that to start charging, but what should the grid disconnect voltage be for charging?

    Alternatively, I have been thinking of setting the grid connect to 9 PM to 5 AM and let the inverter charger have its way during that time period. There wouldn't solar power then, and the inverter charger can then use its fancy bulk, absorb, and float algorithms to get the batteries back to 100%.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: What setting for battery charging from grid?

    I think you've answered your own question. 49 Volts triggers charging, then let it charge. It will stop when it is done.

    This is not like with a generator where you're trying to maximize fuel economy by not running it lightly loaded to finish Absorb and Float.
  • experimenter
    experimenter Registered Users Posts: 20 ✭✭
    Re: What setting for battery charging from grid?

    Thanks to all, especially Cariboo, for the good guidance. Just for my own ultimate clarity, I will set the inverter to connect to the grid power and start recharging the batteries when the battery bank reaches 49.0 volts. I will set the inverter to DISconnect form the grid power once the battery bank reaches 58.0 volts. (I need to set the disconnect voltage as well or the inverter will stay connected to the grid forever.)
  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    Re: What setting for battery charging from grid?
    I will set the inverter to DISconnect form the grid power once the battery bank reaches 58.0 volts. (I need to set the disconnect voltage as well or the inverter will stay connected to the grid forever.)

    The disconnect point will depend on your loads and how much solar power you have available. I would adjust the disconnect point through experimentation, e.g. if the grid connects at 49V, then it could bulk up the batteries to 54V for example, and if you have enough solar available (and aren't drawing too much through your loads), then the solar will take care of finishing bulk and absorb.
    But if you're hammering the system with loads and the solar can't keep up, then you'll need a higher grid disconnect setting.