Battery bank voltage question...

MaineCabin
MaineCabin Solar Expert Posts: 29
Hi,

With the help from this forum I've been able to set up an off-grid cabin. My basic system consists of :

- (2) 15+ year old soalex PV panels
- Morningstar MPPT Sunsaver Charge Controller
- (4) Trojan T-105 batteries
- Xantrex dr1512 Inverter
- Honda 3500 generator

So far the system is working well but I'm concerned about the battery voltages. When I first installed the new batteries they were at 12.60 volts. I ran the system a few weeks with using the generator to charge the batteries and never saw voltages above 12.62.

Now having the Sunsaver going for a week (with very little inverter use) I'm getting voltages of 12.78 and 12.80. This is after resting the batteries overnight.

Is there a problem? Or is this a good thing? Thanks in advance...

I guess I should add that I'm concerned the voltage is too high, I thought a fully charged battery bank is 12.60V

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Battery bank voltage question...

    Sounds pretty good... It is possible that you where undercharging before...

    Wind-Sun has a very good Battery FAQ--if you have not read it yet--do read it in detail. Not only because it has numbers--but it also discusses philosophy of battery operation and care. Understanding what you are trying to achieve can help you figure out how to do that with the equipment you have...

    So, some suggestions... More or less in order of importance (in my humble opinion knowing nothing else about your system):

    1. Get the remote battery temp sensor for the Morning Star controller
    • This will ensure your batteries are accurately charged to 100%
    2. Get a hydrometer and thermometer...
    • This will tell you very quickly the health of your battery bank--both overall level of charge/discharge and if individual cells/batteries are failing. Also can tell you when to force equalization. You will not use this every day--but checking a cell once a week (after you have checked/logged all cells for a day or two of use/charging to make sure everything starts out good) will help you keep the batteries in-charge.
    3. Review your AC Battery Charger... Possibly get one that is designed for deep cycle batteries (and has remote temperature sensor, if IOTA--get the extra board).
    • Many folks use just a plain old multi-purpose battery charger... Many do not output a high enough charging voltage to really fully charge a deep cycle battery. They also cannot equalize (although, usually the solar charge controller + panels will be able to on a sunny day). A good deep cycle battery charger will also, typically, output higher current for more time--so faster/better charging and less fuel wasted on running a gen set at low power usage by your charger.
    4. How much battery water are you using... If a lot every month--you may be over charging (at times). If none--then you probably are not charging enough. If you think you are charging OK--but using excess water/mess on battery top--then look at some sort of "water miser" caps.

    5. Sort of optional (because solution could be more money than you want to spend)... Get a Kill-A-Watt meter and put it on your generator output when charging your batteries...
    • See if a eu3500i may be too large of generator for daily charging of your batteries--perhaps you are using a lot of fuel to only output a few hundred watts. Jacking up the charger size/output and/or using a smaller generator (like the eu2000i--although not electric start) may save you a bunch of money in gasoline. --If you only charge a little bit (during bad weather or when you are using other large loads--like washer/drier/saw/tools/etc... then you are using the generator probably to capacity (as a rough rule, using a generator below 50% capacity is not very fuel efficient--using the Honda euX000i family, if used below 25% capacity--with ECO Throttle On would not be fuel efficient).
    Basically, the Honda family gives you, roughly, around 5,000 to 5,500 Watt*hours (5-5.5 kWhr) per gallon of fuel... Connect the kill-a-watt meter and run your load(s)... See how much power you use, how many kWhrs, and how much fuel you use...

    6. I would also add--look at a battery monitor. Highly recommended, but not cheap. Allows you to see your battery state of charge at anytime under any condition... If it even saves you killing your battery bank once (and early replacement)--you will probably break even at the very least.
    • The Trimetric TM2020 Battery Monitor System has had some love here (good $$/performance). The Xantrex LinkLite/LinkPro family I like a lot because you can set it up to turn off your loads (with a relay, control the inverter) or turn on a Red Light / Alarm on State Of Charge below XX%--really useful for the friend/worker that does not want/need to know to run your fancy off-grid system.
    Home that this is useful--probably pretty repetitive for anyone that has been reading my "rants" over the last couple months (sorry)...

    -Bill

    PS: Probably I should answer your original question ( ;) )--12.70 volts after the battery has rested for a few hours, and at 77F -- is 100% charged---And this also requires that you have an accurate/calibrated voltmeter. You will need to temperature correct the voltage up (if batteries are colder) or down (if batteries are warmer).
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Battery bank voltage question...

    > Xantrex dr1512 Inverter

    Does your inverter have a charger in it also ? The first 70% of the charge goes quickly into the battery, and that's good for a generator to do (efficient loading and fuel use) It's the last 30% that can take several hours (up to twice as long as the first 70%), but that's the important part, to fully charge your batteries. If your weren't running the generator for hours and hours, you never fully charged the batteries. After a week of sun, the PV's got them completely full.
    Now it's time to check the water level, some may have bubbled away. Undercharged batteries seldom need water.


    PS: Battery FAQ says 12.7V = 100% @ 77F
    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 ,

  • shortfatguy
    shortfatguy Solar Expert Posts: 42
    Re: Battery bank voltage question...
    • The Trimetric TM2020 Battery Monitor System has had some love here (good $$/performance). The Xantrex LinkLite/LinkPro family I like a lot because you can set it up to turn off your loads (with a relay, control the inverter) or turn on a Red Light / Alarm on State Of Charge below XX%--really useful for the friend/worker that does not want/need to know to run your fancy off-grid system.

      I didn't know you could use LinkLite/LinkPro to control the inverter. Idiot pproofing is what I'm trying to do so too. Does Xantrex sell the relay setup? Can the same setup be used with the Link 10/20?
  • MaineCabin
    MaineCabin Solar Expert Posts: 29
    Re: Battery bank voltage question...

    Thanks everyone for the responses...

    I've only had the charge controller hooked up for a couple of weeks and I was just concerned the batteries were getting over charged. So far the water level hasn't changed, but it's only been a couple of weeks. I'll keep my eye on them. I do plan on buying a battery monitor in the near future, and a hydrometer.

    I guess the good news is that everything is working and I'm getting a surplus of power! Right now I'm just running a few CFL lights and a water pump, weekends only. I'm hoping to never run the generator!

    Rich
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Battery bank voltage question...
    The Trimetric TM2020 Battery Monitor System has had some love here (good $$/performance). The Xantrex LinkLite/LinkPro family I like a lot because you can set it up to turn off your loads (with a relay, control the inverter) or turn on a Red Light / Alarm on State Of Charge below XX%--really useful for the friend/worker that does not want/need to know to run your fancy off-grid system.
    I didn't know you could use LinkLite/LinkPro to control the inverter. Idiot proofing is what I'm trying to do so too. Does Xantrex sell the relay setup? Can the same setup be used with the Link 10/20?

    SFG,

    There is a "QUOTE" button at the bottom of each post--it will make it much easier to follow the cuts and paste between you and others... (you will see the world quote between a left and right bracket--and for the end [/quote] )

    Your question--while you can get a big relay and set it up to control the DC power to your inverter... You are better off getting an inverter that has an on/off input (usually 5 or 12 volt signal) that can be driven by the LinkXxx controller (the LinkXxxx controller is just a small signal--12 volts at a few 10's of mAmps--IIRC). Controlling a big relay can actually waste 10 watts or so of power just turning it on (depends on the size of your system if 10 watts or so of wasted power will hurt you or not).

    The older Link 10/20 does not have the external contact output--that I know off... I don't remember seeing this type of contact on any other of the Battery Monitors--but this was just recreational reading (:p)--I do not currently have any applications for this equipment--so I have not paid close attention (and I am not employed by NAWS or by anyone else in the solar industry).

    If your needs are small--MorningStar makes a very nice 300 watt true sine inverter with very low losses.

    Morningstar SureSine, 300 Watt Sine Wave Inverter 115VAC

    Other brands, with small and larger inverters also have the aux switch control... You will probably need to pick a size, and read through the manual for the details:

    For example, at least a couple Exceltech have a an AUX control (XP1100 & XP600 Complete Owners Manual + Specs PDF manual).

    The other brands (such as available at Wind Sun / NAWS, also a good inverter FAQ if you want to learn a bit more), you will have to look up a manuals and search the web/mfg. site for details.

    I do not have access to any of these devices--so I would be doing the same as you--picking a couple devices and reading the manual--Then make sure that the input/outputs are compatible--and calling the Mfg. if something is not clear.

    If you are unsure--calling NAWS or the Mfg. directly should get the exact answers you need. We can certainly direct you towards possible solutions.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Battery bank voltage question...
    MaineCabin wrote: »
    I've only had the charge controller hooked up for a couple of weeks and I was just concerned the batteries were getting over charged. So far the water level hasn't changed, but it's only been a couple of weeks. I'll keep my eye on them. I do plan on buying a battery monitor in the near future, and a hydrometer.

    If the batteries are not getting Hot and/or bubbling a lot (boiling more than just a gentile fizz--like an open soft drink)--you are probably not overcharging.

    For now, the flooded cell batteries are a good start for you... Even if you are somewhat overcharging--you can add water... The AGM and other sealed batteries--overcharge at all--and you kill them.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • halfcrazy
    halfcrazy Solar Expert Posts: 720 ✭✭✭
    Re: Battery bank voltage question...

    Rich i am guessing you have a cabin in Maine? what part of Maine? whe are in central maine and just stood our wind turbine today
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Battery bank voltage question...

    You should seriously look into initiating an EQUALIZE charge from your charge controller. The question is, do you have enough PV to generate enough power, to complete the cycle in one day ?

    I suspect the batteries have been deficit charging long enough, an EQ should happen soon.
    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 ,

  • shortfatguy
    shortfatguy Solar Expert Posts: 42
    Re: Battery bank voltage question...
    BB. wrote: »
    SFG,

    There is a "QUOTE" button at the bottom of each post--it will make it much easier to follow the cuts and paste between you and others... (you will see the world quote between a left and right bracket--and for the end
    )

    [/QUOTE]


    Thank you for the information.
  • MaineCabin
    MaineCabin Solar Expert Posts: 29
    Re: Battery bank voltage question...
    halfcrazy wrote: »
    Rich i am guessing you have a cabin in Maine? what part of Maine? whe are in central maine and just stood our wind turbine today

    Were in Downeast Maine. Marion Township in Washington County. Looks like you've got a pretty nice off-grid system. Good luck with your wind turbine...

    Rich
  • MaineCabin
    MaineCabin Solar Expert Posts: 29
    Re: Battery bank voltage question...
    mike90045 wrote: »
    You should seriously look into initiating an EQUALIZE charge from your charge controller. The question is, do you have enough PV to generate enough power, to complete the cycle in one day ?

    I suspect the batteries have been deficit charging long enough, an EQ should happen soon.

    I will try this thanks...