Battery Charging

TobyToby Solar Expert Posts: 56 ✭✭✭✭
How could I charge an AGM battery bank using commercial power?

I'm looking into using batteries for an emergency back up power system. Battery power will go though an inverter to supply AC power as needed in the event commercial power is lost.

What would I use to keep the AGM batteries properly charged? Do charge controllers accept AC power or just DC from panels, wind, etc.

Thanks.

Comments

  • mike95490mike95490 Solar Expert Posts: 9,320 ✭✭✭✭✭
    Re: Battery Charging

    You would need need an AC (mains) powered 3 stage battery charger.

    What voltage is your system ?

    Amp capacity of the charger, how often do you expect to loose and regain power, if only once a year, a small charger is fine, as long as it can recharge bank in 24 hours. If you expect 1 or 2 daily outages, you need a beefier charger, to recharge before the next outage.
    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 ,

  • TobyToby Solar Expert Posts: 56 ✭✭✭✭
    Re: Battery Charging

    Hi Mike,

    Battery bank and Inverter would be 24 volt.

    The system would be for those unexpected, "once a year" commercial power outages. An emergency generator that requires no liquid fuel.

    Can you recommend any particular brand/model of charger? Can you explain what you mean by 3 stage?

    Thanks.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Battery Charging

    If you're going to need the inverter you might as well buy one with a built-in charger. The Magnum's have 3 stage charging with very good Power Factor correction: http://www.solar-electric.com/maensiwainac.html

    You'll also want to peruse the battery FAQ's to get an understanding of the whole process: http://www.windsun.com/Batteries/Battery_FAQ.htm

    Do you have a figure for how much power you'll want to supply, both in terms of maximum Watts and total Watt hours? This is very important to picking an inverter and battery bank size.
  • TobyToby Solar Expert Posts: 56 ✭✭✭✭
    Re: Battery Charging

    I noticed this charger at W&S http://www.solar-electric.com/iodl24vo15am.html but I do see your point about charger/inverter in one package. That was going to be a follow up question. Separate charger and inverter or all-in-one.

    No specific watt hours selected just yet. Still studying.

    Does the battery FAQ address charger amperage vs battery bank size? I see that the Iota chargers are amp rated. Is there a correlation between battery bank amp hours and charger amperage size?

    Thanks.
  • BB.BB. Super Moderators, Administrators Posts: 31,875 admin
    Re: Battery Charging

    More or less, the rules of thumb we start with here are 5%-13% for solar; and you can go as much as 5%-25% rate of charge for solar/AC Battery Chargers. I.e., 100 AH battery bank, 5 amps to 13 amps to 25 amps.

    A 3 stage charger (with battery float stage) at a minimum (for grid connected AC charger). A Remote Battery Temperature Sensor is good if the batteries change temperatures a lot (not in climate controlled room, and/or charger not in same room as batteries) is nice--you can get quicker/fuller charge with a RBTS.

    If you are going to use a back up genset--then you need to size the battery charger + genset together.

    One suggestion--I am a big believer in matching generator to battery charger to battery bank--and optimize to use as small as genset as practical (while maintaining a minimum of 50% generator AC loading for good fuel economy).

    A lot of what you choose will depends on your specifications.
    • peak power
    • energy (watt*hours) per day
    • how many days of battery backup
    • usage (backup, off grid)
    • generator backup? Fuel type? Days of backup power?
    • etc.
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • TobyToby Solar Expert Posts: 56 ✭✭✭✭
    Re: Battery Charging

    Very good information. Thanks.

    A couple other questions.

    I read through the battery faq. Need clarifiation. If a battery is rated at 200 amp hrs @ 20 hours, how does that relate to the level of discharge? I believe I read that you do not want to draw down the battery over 50%. Does that mean that a 200 amp hr battery can only deliver 100 amp hrs with out going into a deep discharge? I hope that makes sense.


    Also, other than cost and wire size, are there any other advantages/disadvantages in using a 48 volt dc inverter over a 24 dc volt inverter? Seems like 24 volt dc inverters are used more than 48 volt.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Battery Charging
    Toby wrote: »
    Very good information. Thanks.

    A couple other questions.

    I read through the battery faq. Need clarifiation. If a battery is rated at 200 amp hrs @ 20 hours, how does that relate to the level of discharge? I believe I read that you do not want to draw down the battery over 50%. Does that mean that a 200 amp hr battery can only deliver 100 amp hrs with out going into a deep discharge? I hope that makes sense.

    Yes, that's pretty much what it means.

    Also, other than cost and wire size, are there any other advantages/disadvantages in using a 48 volt dc inverter over a 24 dc volt inverter? Seems like 24 volt dc inverters are used more than 48 volt.

    There's advantages and disadvantages to both. In general terms you go up in system Voltage when maximum Watts needed or daily Watt hours needed rise above a practical threshold.
    Basically the problem is that as power needs increase, so does current. Higher current is harder to handle, more of it goes to heat, and wiring becomes problematic. So if you have a particular power level in mind you should look at the lower and the higher Voltage set-up and see what the difference is. As a guideline, ever 2 kW of peak power or 2400 Watt hours daily you should at least consider the next level of system Voltage. For really high power requirements you should consider splitting loads off into separate autonomous systems.
  • TobyToby Solar Expert Posts: 56 ✭✭✭✭
    Re: Battery Charging

    Ok, that makes sense on the battery question.

    So, in simplest terms is this correct?

    0 - 2400 watt hours = 12 volt
    2400 - 4800 watt hours = 24 volt
    4800 - 7200 watt hours = 48 volt
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Battery Charging
    Toby wrote: »
    Ok, that makes sense on the battery question.

    So, in simplest terms is this correct?

    0 - 2400 watt hours = 12 volt
    2400 - 4800 watt hours = 24 volt
    4800 - 7200 watt hours = 48 volt

    Let's say that within those parameters you have the thresholds where you need to consider one system Voltage over another.
    For instance, using the least-cost batteries (golf cart type) you need two minimum for a 12 Volt system. At 225 Amp hours that will provide up to 1200 Watt hours (more or less - disregarding efficiency factors) at 50% DOD. Double those batteries to get 2400 Watt hours. Now you've got four which can also be wired in series for 24 Volts. Same batteries, same over-all power potential in Watt hours. But at 24 Volts you have simplified the battery wiring (all in series; less difficulty with keeping current flow even) and reduced the charge current from what would be (ideally) 45 Amps on the 12 Volt system to 22.5 Amps on the 24 Volt system. Less current = less problems handling the current. Higher Voltage allow for longer and/or smaller wire sizes with less power loss.

    It's a balancing act, and admittedly a very complex one.
  • BB.BB. Super Moderators, Administrators Posts: 31,875 admin
    Re: Battery Charging

    And the borders are a bit fuzzy... You might consider 1,200 watts maximum for a 12 volt system (>100 amps of power from battery bank).

    Many times, you end up designing the same system in both 12 and 24 (or 48) volts to see what the trade-offs are (different vendors cover different voltage ranges, different current ranges, different options, etc.)...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • TobyToby Solar Expert Posts: 56 ✭✭✭✭
    Re: Battery Charging

    Just when I thought I starting to understand this solar stuff ........

    Give me a few days to digest the info you have just provided.

    Again, thanks for the help.
  • BB.BB. Super Moderators, Administrators Posts: 31,875 admin
    Re: Battery Charging

    Not trying to confuse you... We try to give "hard numbers" as rules of thumb/guidelines to make things easier as a starting point... But, of course, everything is a set of gray areas.

    Doubly true when you start to look at things like an engineer and take "extreme conditions" into account.

    In simple terms, Power = Voltage * Current... So a 1,200 watt running on 12 volt battery bank would take:
    • 1,200 watts / 12 volts = 100 amps
    The details... The low voltage cutoff for the typical 12 volt inverter is 10.5 volts (11.5 volt battery voltage and ~1 volt wiring/fuse drop). Add 85% for inverter efficiency and a 1.25 NEC safety factor (wires and breakers need to be 1.25x larger than "continuous current load"--fuses and breakers are designed to eventually trip at rated current/load):
    • 1,200 watts * 1/0.85 inverter eff * 1/10.5 volts cutoff * 1.25 NEC safety factor = 168 Amp Circuit/Fuse/Breaker rating
    So--you are now looking at 175-200 amp wiring to manage "worst case" maximum current. Not the "100 amps" that we would have first thought using P=V*I

    Also, when "picking" a bank voltage--we are looking at inverter which are designed for 12, 24, or 48 volt battery banks. If you up the battery voltage, you need to purchase a new inverter.

    However, most charge controllers are designed to manage 12 or 24 volts, and some even 48 volt battery banks. And they are rated at maximum output current. So, as you go with higher battery bank voltages, they charge controller can actually manage a larger array without having to purchase a second or larger controller.

    For example, 60 amp 12/24/48 volt output MPPT charge controller and using a 0.77 derating factor. Roughly, the maximum solar array such a charger can (cost effectively manage) is:
    • 60 amps * 14.5 volts charging * 1/0.77 derating = 1,130 watt array @ 12 volt bank
    • 60 amps * 29.0 volts charging * 1/0.77 derating = 2,260 watt array @ 24 volt bank
    • 60 amps * 58.0 volts charging * 1/0.77 derating = 4,519 watt array @ 48 volt bank
    Note that I am carrying lots of figures--the numbers are not really that accurate/set in stone--Just doing this so you can reproduce my math.

    So, depending on the size of your loads, and/or inverter loads--May push you up to higher voltage battery bank.

    Or, you could have low peak current, but running your smaller loads 24 hours per day... So the solar array needs to be large to recover all of the charging current in 4-6 hours of sunlight--so you may want a higher battery bank voltage so you can use one controller instead of two (or four) and save money that way.

    There are lots of other rules of thumbs/recommendations that can discuss too... But starting with your loads and battery bank helps guide the rest of the design process (maximum current, bank voltage, etc.).

    Hope this is more helpful--rather than more confusing.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • TobyToby Solar Expert Posts: 56 ✭✭✭✭
    Re: Battery Charging

    This is all great information and I really appreciate the time you guys take to type the lengthly explanations.

    I learn something each time I read a post here. Most times they make me step back a bit with what I thought I understood. That is a good thing, at least for me. I don't want to start my power project until I really understand it.

    The best part is, I know a lot more now than when I started! So yes, what you wrote below Bill cleared up some other questions I had.

    Thanks!
  • TobyToby Solar Expert Posts: 56 ✭✭✭✭
    Re: Battery Charging

    In another reply, a Magnum Energy inverter was recommended. I'm looking at the 48 volt model:

    http://www.magnumenergy.com/Literature/Data%20Sheets/Inverters/64-0275%20Rev%20A%20(MS-PAE%20Series%20Data%20Sheet).pdf

    In the future I may decide to add solar panels which would require a charge controller. Since the inverter includes a battery charger, does the inverter know which to use to charge the batteries?

    If there is sufficient sun light for the panels/charge controller to operate, the batteries are charged off the panels? And if insufficent sun light the batteries are charged from line voltage power?

    I may need to dig into the product manual but was wondering if this charging scenario is standard for most inverters.
  • BB.BB. Super Moderators, Administrators Posts: 31,875 admin
    Re: Battery Charging

    Solar PV systems are getting more complex all the time... But from a basic point of view, the inverter/charger has a straight forward 120 (or 240) VAC battery charger built in... It will charge the battery bank if there is 120 VAC power on the inverter input... Really just the electrical part of a UPS without the internal batteries.

    If you have solar panels, you will need to add a Solar Charge Controller between the panels and your battery bank. Depending on how the inverter/charger is designed, you may be able to (or not) turn off the AC battery charger portion.

    You can parallel multiple battery chargers inverter/CHARGER, Solar Charge Controller, Wind Turbine, genset, etc... For the most part, they will play OK together (the Wind Turbine charger is typically a shunt/bypass/dump controller--if setup incorrectly, it could dump power from your AC mains to the resistor bank and cost a large power bill).

    It does get even more complex... There are Hybrid Inverters--Really Grid Tied / Off Grid / Inverter / Chargers that can take the excess charge current from the solar array/battery bank and send it out through its Grid Tied Interface (Xantrex XW Hybrid Inverter System, some Outback units, etc.).

    But, normally, you would need building permits and utility approval for any sort of Grid Tied system (selling power back to the utility).

    Normally, I suggest going back to basics... What is it you want from your system (power, backup, solar, grid tied, how much money, etc.) and then design from that point out.

    If we discuss all possibilities with aiming at an end goal--it gets real confusing/ugly real fast.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Battery Charging
    Toby wrote: »
    In another reply, a Magnum Energy inverter was recommended. I'm looking at the 48 volt model:

    http://www.magnumenergy.com/Literature/Data%20Sheets/Inverters/64-0275%20Rev%20A%20(MS-PAE%20Series%20Data%20Sheet).pdf

    In the future I may decide to add solar panels which would require a charge controller. Since the inverter includes a battery charger, does the inverter know which to use to charge the batteries?

    If there is sufficient sun light for the panels/charge controller to operate, the batteries are charged off the panels? And if insufficent sun light the batteries are charged from line voltage power?

    I may need to dig into the product manual but was wondering if this charging scenario is standard for most inverters.

    Yes, and then again no. The batteries don't care if they get charge from two sources; each will regulate itself against the other. The inverter will try to charge any time it senses AC IN has proper Voltage present. Fully integrated systems like Outback allow inverter and charge controller to communicate and share data like charge set points, battery Voltage, and battery temperature. Most of the time this is not a big issue as the generator charging is used for the Bulk stage and the more precise solar power can "finish the job" even on cloudy days. It's just a bit less "automatic" with mixed components. It's also less expensive.
  • TobyToby Solar Expert Posts: 56 ✭✭✭✭
    Re: Battery Charging

    Once I thought about it after posting the questions, I was almost sure it would work as I explained it.

    I realized that the solar charge controller (example MS Tristar MPPT) is between the panels and the battery. Likewise the inverter battery charger is between the line voltage and the batteries. Inverter charger and solar charge controller would both be wired to the battery and both could feed battery charge voltage.

    I read both of your replys to concur that mixing those two components to charge the batteries will work, and as Cariboocoot mentioned, would be cheaper than an integrated battery charger/charge controller inverter?

    Right now I have a 200 amp manual transfer switch to which I can plug-in a 7500 watt gas generator. I just switch off the breakers for the high watt items like water heater, HVAC, stove, etc. I can turn On anything in the house I want as long as I have fuel!

    So, the next plan is a battery powered emergency backup for the house.

    Somewhere around 4kw.
    Initially connected to utility power to keep the batteries charged. Solar eventially.

    But, just like gas fuel for the generator, I also need battery fuel for the inverter. Nothing is ever simple or inexpensive!
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Battery Charging

    I don't want to sound like that English teacher everybody hated but ...

    There's no such thing as an "integrated battery charger/charge controller inverter".

    Charge controllers are separate entities.
    Some inverters have built-in battery chargers and can be called Inverter/Chargers.
    Some inverters don't, but you can use a stand-alone battery charger.
    Batteries don't care how many charge sources there are, and neither do the charge sources; they self-regulate, with whichever one has the highest Voltage settings inevitably taking over.
    There are integrated solar power systems where the charge controller and inverter (usually an inverter/charger) "talk" to each other so that important data like charge set points and battery temp are shared.

    Lots of words and confusing terminology I know.

    As for AC switching, if you have an inverter/charger it will detect incoming AC and transfer loads to that source while operating as a battery charger.
    More complex switching can be done with AC sourcing from generator or grid (why are we talking solar off-grid if the utility is available? I don't know!) so that a line from the gen can feed the inverter/charger and another can power high-demand loads that otherwise would be left off-line.

    Lots of possibilities. All of it technical. :cry:
  • TobyToby Solar Expert Posts: 56 ✭✭✭✭
    Re: Battery Charging

    Ok, I misunderstood when you wrote, "Fully integrated systems like Outback allow inverter and charge controller ...."

    I'm in the planning stage so I have lots to study, question, comprehend, and then make a decision.

    I'm planning for a standby system. No AC switching. I'll conncet it to the transfer switch if needed. Grid power is to keep the batteries charged until I decide if I want to add solar. Maybe AC switching in the future too.

    This probably sounds like a strange set-up, but that is what I'm planning for right now. Taking small steps.

    Please understand I'm learning and will make wrong assumptions. That's why I'm here asking and learning.

    I do appreciate your time and I know it can be frustrating answering similar questions from beginners.

    Again, thanks.
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