Basic Battery Questions

richrich Solar Expert Posts: 62 ✭✭✭✭
Hello, im new here, not sure if its ok to ask a battery question here(or if the mod would prefer I start a thread...???)...here goes it...im having problems finding what the" at rest" voltage reading should be , these batteries(x4) are excide E 3600 6 volt commercial deep cycle batteries. Any info would be great. Also, is the at rest voltage specific to a battery brand or the same across the board..thanks, Ive been a bit of a lurker here..

Comments

  • BB.BB. Super Moderators, Administrators Posts: 29,485 admin
    Re: Basic Battery Questions

    Welcome to the Forum Rich.

    I moved your question to its own thread... Hopefully, that will help you to guide the discussion towards your ends.

    First, a few Battery FAQs:

    http://www.windsun.com/Batteries/Battery_FAQ.htm
    http://www.batteryfaq.org/
    http://batteryuniversity.com/

    There is some more battery information scattered throughout this thread (and some battery history too):

    Working Thread for Solar Beginner Post/FAQ


    The problem with measuring battery voltage to estimate its state of charge is there are many variables that affect the battery voltage... Here is an interesting set of graphs that indicate the issue:
    leaf wrote: »
    Am trying to upload the charts I am using...

    Attachment not found.Attachment not found.

    attachment.php?attachmentid=3655

    attachment.php?attachmentid=3654

    I don't quite a agree with the resting voltage line (I think the voltage is a bit low)--But it shows how to estimate a battery's state of charge while operating.

    Note, where the charts "flatten out"--the room for error estimating state of charge is pretty high.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BB.BB. Super Moderators, Administrators Posts: 29,485 admin
    Re: Basic Battery Questions

    SG factory levels are "variable":
    BB. wrote: »
    Here is a thread on Hydrometers and how best to use them.

    I understand that some tropical locations will use a bit weaker electrolyte (batteries will have a longer service life?).

    From this thread, the range of Electrolyte Specific Gravity seems to be:
    Specific Gravity vs Applications
    1.285 Heavily cycled batteries such as for forklifts (traction).
    1.260 Automotive (SLI)
    1.250 UPS – Standby with high momentary discharge current requirement.
    1.215 General applications such as power utility and telephone.

    As mentioned earlier, the specific gravity (spgr.) of a fully charged industrial battery, or traction battery, is generally 1.285, depending on the manufacturer and type. Some manufacturers use specific gravities as high as 1.320 in an attempt to gain additional Ah capacity, but at the cost of a shorter cycle life.

    ...

    Higher Gravity = vs Lower Gravity =
    More capacity / Less capacity
    Shorter life / Longer life
    Higher momentary discharge rates / Lower momentary discharge rates
    Less adaptable to "floating: operation / More adaptable to "floating" operation
    More standing loss / Less standing loss
    So, where do your readings fall in the above scale... And I would guess that a difference of 0.030 SG or less is nothing to panic over.

    And while there is a formula for converting from SG to Cell voltage:
    Specific gravity = single-cell open-circuit voltage - 0.845 (example: 2.13v – 0.845 = 1.285)
    Or
    Single-cell open circuit voltage = specific gravity + 0.845.

    Battery temperature, additives to battery plates, voltage measured when battery has not "rested" for 3 or more hour, etc. can all affect the readings.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Basic Battery Questions
    rich wrote: »
    Also, is the at rest voltage specific to a battery brand or the same across the board.

    Basically it's specific to a type of battery: one "cell" of a lead-acid battery produces about 2.125 Volts. Lithium-ion is different per cell, nickle-cadmium is different per cell, et cetera.

    So just about any lead-acid battery "6 Volt" battery would have an ideal resting Voltage of 6.375. This will vary a bit as things like temperature, age, actual specific gravity, and quality of the meter taking the reading will enter in to it.
  • richrich Solar Expert Posts: 62 ✭✭✭✭
    Re: Basic Battery Questions

    Wow thanks for such a quick reply from All...im just second guessing my batteries based on a new crappy-tire charger, when my batteries (two strings of two)are at rest at 12.6 volts the charger says they are below 50 % they seem to only show full right after being charged...then within an hour it says 80%....and the next day they say below 50 %....my 10 second load tester shows them to be good ...im confused, I will be getting the specific gravity thingie later today....thanx All.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Basic Battery Questions

    Yes, to accurately take an at rest Voltage the batteries have to sit with no current in or out for a long time. Preferably over night.

    The thing about charging deep cycle batteries is that they have to be held at the Absorb Voltage for long enough to complete the charge. Not all chargers will do this. I had one of those "intelligent" chargers from CT; took it back as it was dumber than a manual charger.

    The other thing about Voltage as a SOC indicator is that it can be "correct" but the batteries may be sulphated and lack actual capacity. You can't beat a hydrometer reading specific gravity for really knowing what's going on inside.
  • richrich Solar Expert Posts: 62 ✭✭✭✭
    Re: Basic Battery Questions
    Yes, to accurately take an at rest Voltage the batteries have to sit with no current in or out for a long time. Preferably over night.

    The thing about charging deep cycle batteries is that they have to be held at the Absorb Voltage for long enough to complete the charge. Not all chargers will do this. I had one of those "intelligent" chargers from CT; took it back as it was dumber than a manual charger.

    The other thing about Voltage as a SOC indicator is that it can be "correct" but the batteries may be sulphated and lack actual capacity. You can't beat a hydrometer reading specific gravity for really knowing what's going on inside.
    .. OK well noted , the batteries in question were purchased about a week ago..im starting to think this charger may be the same one U had....hmmm.I will be returning it today, any charger You can recommend? that has long term viability and is proven , my budget is around a hundred loones...
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Basic Battery Questions

    Unfortunately off-the-shelf 3 stage deep cycle chargers tend to cost quite a bit. Example: http://www.solar-electric.com/ioen12vo15am.html

    Try finding one of those up here for that money!

    What are you expecting to do with these batteries long-term?
  • richrich Solar Expert Posts: 62 ✭✭✭✭
    Re: Basic Battery Questions

    To make a long story short ...A few years ago I got laid off in the oil patch when the slowdown came.I lost my house,my truck and many of my life long posessions ..I ended up living in a jeep Cherokee with my dog, I swore I would never be homeless again.Im back on my feet again(man its hard without credit) and am converting a heavy-duty enclosed car hauler into sort of a bug-out or survival trailer, hey if it goes from bad to worse ill still have my paid for ram 3500 and trailer...I was hoping to be able to power lights / chargers and maby an efficient fridge....c.b. radio, things of this nature, I also have 735 watts in panels and a cobbled togeather diy control board,(mostly Chinese and indian components) ill try post pics soon if anyone is interested...I came to this forum in hopes of fine tuning my UTUBE knowledge of solar...from ,well the experienced and knowledgable...oh by the way, I ordered the 30 amp model(with IQ4 control) of the charger link u posted...thanks
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Basic Battery Questions

    Fair enough. :D

    The thing about off-gridding is ... buy the batteries last. That way you already have the charge source in place and they don't start going sour on you right away due to lack of charging. 735 Watts of panels ought to do it, providing your cobbled together charge controller works. If it doesn't ... well you're looking at roughly 40 Amps of uncontrolled current hitting those batteries (assuming a 12 Volt system).
  • richrich Solar Expert Posts: 62 ✭✭✭✭
    Re: Basic Battery Questions
    Fair enough. :D

    The thing about off-gridding is ... buy the batteries last. That way you already have the charge source in place and they don't start going sour on you right away due to lack of charging. 735 Watts of panels ought to do it, providing your cobbled together charge controller works. If it doesn't ... well you're looking at roughly 40 Amps of uncontrolled current hitting those batteries (assuming a 12 Volt system).
    LOL.bzzzzzt!!!..yup the import junk seems to be working ...eats up 3/4 of a volt somewere tho, only time will tell its true potential. I cycled it for two weeks with a couple old giant tugboat batteries ive had for several years...they still held charge and load tested not bad(very surprised)...using battery chargers to simulate wind and solar, I will connect my new exides tomorrow. Damn U guys have an awesome site here!
  • richrich Solar Expert Posts: 62 ✭✭✭✭
    Re: Basic Battery Questions
    BB. wrote: »
    Welcome to the Forum Rich.

    I moved your question to its own thread... Hopefully, that will help you to guide the discussion towards your ends.

    First, a few Battery FAQs:

    http://www.windsun.com/Batteries/Battery_FAQ.htm
    http://www.batteryfaq.org/
    http://batteryuniversity.com/

    There is some more battery information scattered throughout this thread (and some battery history too):

    Working Thread for Solar Beginner Post/FAQ


    The problem with measuring battery voltage to estimate its state of charge is there are many variables that affect the battery voltage... Here is an interesting set of graphs that indicate the issue:



    attachment.php?attachmentid=3655

    attachment.php?attachmentid=3654

    I don't quite a agree with the resting voltage line (I think the voltage is a bit low)--But it shows how to estimate a battery's state of charge while operating.

    Note, where the charts "flatten out"--the room for error estimating state of charge is pretty high.

    -Bill

    Funny thing...seems that the graph would show resting at a low 12.6 ish, that's were mine seem to be sitting after a night of rest....it was the charger for sure , as was mentioned by the other Mod, it says my batteries are low while resting (below 50%)....Ive ordered a 30 amp deep cycle friendly charger from the site sponsors...they have a really good sale right now, it was approx. half price...I also see charge controls and inverters on sale....god my g/f/.is gonna kill me!...I would like to thank the mods here and the resident experts.....great site!
  • BB.BB. Super Moderators, Administrators Posts: 29,485 admin
    Re: Basic Battery Questions

    When ordering trans-national boundaries... Be sure you understand the costs at the border (and any local GST taxes).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • richrich Solar Expert Posts: 62 ✭✭✭✭
    Re: Basic Battery Questions

    Yup good point...it seems I usually pay aroud 20 bucks for two panels ,but varies, I can get a similar panel from china and never pay any duty, not sure why..As it is I see it as part of doing business...thanx for the advice..
  • richrich Solar Expert Posts: 62 ✭✭✭✭
    Re: Basic Battery Questions
    Unfortunately off-the-shelf 3 stage deep cycle chargers tend to cost quite a bit. Example: http://www.solar-electric.com/ioen12vo15am.html

    Try finding one of those up here for that money!

    What are you expecting to do with these batteries long-term?
    Hey Cariboocoot, the 30 amp version of the charger that You so kindly linked Me too, have You ever heard of any issues with having it hooked parallel to existing equipment or would You recommend not doing so .Also,:D reading further into some of your thread advice to others I may be in trouble the way I have wired my set-up, as regarding the additional wind turbine input, I will try to draw up a basic diagram and pics before I pose some questions...anyway thanks so far for Your input.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Basic Battery Questions

    As a rule parallel charge sources are not a problem. The difficulties that will arise stem from two things: inability to get the different regulators to agree on Voltage and set points; problems with excess current in Bulk stage if the total of all sources exceeds the max recommended for the batteries.

    Both of these can be dealt with. In the case of the first issue the charger with the most power tends to "win out", so you have to think about which is going to give you that power and hold Absorb at the right level long enough, et cetera. As such you end up with a primary charge source and the others just contribute to the Bulk stage. Since this is normally done just with solar & controllers the current issue usually doesn't exist as you would be planning on running all at the same time anyway.

    The current problem usually arises from the combination of solar operating in good sun and a generator being used to power heavy loads. If that gen is also set to do full charging when there is no sun you can have full current from solar + full current from AC source charger. If this is a likely problem to recur then you need some method of interrupting one charge source or the other so that the batteries can't receive 2X maximum Bulk current. The simplest way is to have the AC activate a relay that interrupts the solar panels to the charge controller.

    But since ever situation is different generalizing like this can lead to wrong conclusions. So let's see that diagram! :D
  • richrich Solar Expert Posts: 62 ✭✭✭✭
    Re: Basic Battery Questions

    Hello forum, in the last few weeks Ive read an amazing amount of stuff and averted certain disaster with my 3 phase AC conversion, ( another mislead consumer with a dangerious amount of electrical k(no)w-how )lol...Ive ditched the wind turbine idea in favor of gearing in a water wheel on a boom type set-up(will be a different thread).....anyway.....

    Here goes my set-up.....Is anybody famliar with trak-max, sold by windy nation, ???. I am using a trak-max 40 amp MPPT regulator, 8- 1oo watt pannels ,4 exide gl3600 traction batteries and all applicable fusing and shut-offs...the pannels will run series of 2 and 4 parallel inputs to the buss, I have upgraded to 24 volt charging and system.....This will be required to run a 75 watt bar fridge from an ineficcient noisy Chinese inverter 24/7...it will also need to power photo controlled exterior lights up to ten hours a night, 30 watts.this hasnt been commisioned yet..IT will have genny back-up. Any ideas?

    My 12 volt equipment will be used in a separate system with two smaller battereis and a 135 watt pannel, it runs the computer and all inhouse lighting of up to 25 watts for short periods. this set-up is now tried and true....I will be ditching the giant commercial marine battery for two small 12 volt type RE units in the near future.

    Here is the question i pose to the members, Will i need to keep the 24 v system ground separate from the trailer chassis ground?..is there any reason I "need" to ground either system to the chassis ground,(over and above electricle boxes and pannel mounts) I see the experts agree to disagree on some seemingly simple grounding issues/advice......any input would be great and any experience with the for-mentioned windy nation charge control would be great!.... and 1 more thing, I hope We are all having fun and staying safe...summer is winding down.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Basic Battery Questions

    I see no reason why the grounds of two systems of two different Voltages can't be tied together.

    But, if they are also grounded on the AC side you could run into problems with different inverter types. Notoriously MSW inverters do not like their AC output grounded.

    So you have the negatives of the two systems both tied to Earth ground: no problem.
    Start tying other wires of the same two systems together: problems can arise.
  • richrich Solar Expert Posts: 62 ✭✭✭✭
    Re: Basic Battery Questions

    Were are all my posts and replies going??????.....thanx Mods! all fixed!
  • richrich Solar Expert Posts: 62 ✭✭✭✭
    Re: Basic Battery Questions

    Yes, no other wires tied...the chassis ground will be only dc and dc equipment.....thats a go then...now bieng shy to ground the ac side would it be safe to say that i can use a ground to earth rod?..im wondering also why my thread seems to be broken up and fragmented, i cant seem to see it all in one"thread".......
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Basic Battery Questions
    rich wrote: »
    Yes, no other wires tied...the chassis ground will be only dc and dc equipment.....thats a go then...now bieng shy to ground the ac side would it be safe to say that i can use a ground to earth rod?..im wondering also why my thread seems to be broken up and fragmented, i cant seem to see it all in one"thread".......

    Hmm. It's looking perfectly normal here. :confused:

    Grounding the AC side is going to depend on what the particular inverters want. For example one with a built-in GFCI outlet will want its case grounded, but no connection between neutral and ground after the GFCI because there's already one inside. Likewise an MSW inverter may not be able to take an N-G bond at all.

    If the AC is left "floating" (neither side tied to ground) it should be protected by a dual common-trip breaker so that any over-current condition will disconnect both sides; "hot" and "neutral".
  • BB.BB. Super Moderators, Administrators Posts: 29,485 admin
    Re: Basic Battery Questions

    Rich,

    There are various thread display options... I have set you to the old tried and true:

    Thread Display Mode
    • Linear - Oldest First
    • Linear - Newest First
    • Hybrid
    • Threaded

    Linear, oldest first. You had "Hybrid" selected.

    There is a "SETTINGS" link in the upper right of the screen. You can click through there and go to GENERAL SETTINGS and play with the various options... Or click on this link:

    http://forum.solar-electric.com/profile.php?do=editoptions

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • richrich Solar Expert Posts: 62 ✭✭✭✭
    Re: Basic Battery Questions

    Thank You Bill, ....im old tried and true so it will work....;)
  • richrich Solar Expert Posts: 62 ✭✭✭✭
    Re: Basic Battery Questions

    At this point i am sure the GFCI thing is not the case...but in all simplicity i will go with the dual breaker, one at each end- hot and nuetral, it seems an easier solution, possibly the safest to address this, thanks again to coot/bill....u guys are true leaders and helpers....and they give Oh blamma a peace prize....sheesh...thanks again I will go back to lurking.....;0
  • BB.BB. Super Moderators, Administrators Posts: 29,485 admin
    Re: Basic Battery Questions

    And a big thank you to the rest of the folks on the forum. A very nice/well behaved bunch that answer way more questions than us moderators could ever do by ourselves (oh--You want correct answers too? :p).

    Really a forum that demonstrats the whole is more than just the sum of the pieces.

    Not to forget NAWS (Northern Arizona Wind & Sun) for hosting the forum + paying the bills. They set the ground rules years ago and pretty much let the forum run itself with volunteers.

    -Bill :-)
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • richrich Solar Expert Posts: 62 ✭✭✭✭
    Re: Basic Battery Questions

    we run 24 volt panels on a 12 volt battery bank using a MPPT CC. We have NO issues going into float and absorb daily. 740 watts solar on 900+ AH battery bank. We only pull 150 ah while we have been using power tools. thats less than 25% draw on batteries. We also have wind turbine charging on most days, We have 2 245 watt 24 volt panels not in use if required. Thanks for the information. I have been told by professionals I over built the solar and wind for our battery bank........would this be a correct statement..im trying to help a fella get this straight.......thanks
  • BB.BB. Super Moderators, Administrators Posts: 29,485 admin
    Re: Basic Battery Questions

    Loads define -> Batteries

    Batteries define -> Charging source Ampacity

    Loads define -> Solar array Watts

    So, using what you have told us... 150 Amp*Hours per day on a 24 volt battery bank. 1-3 days of "no sun" and 50% maximum discharge is the rule of thumb. Pick 2 days + 50% maximum discharge as a well balanced system:
    • 150 AH * 1/0.85 inverter eff * 2 days * 1/0.50 max discharge = 705 AH @ 24 volt battery bank

    Your 900 AH battery bank is a bit on the large side--But not by that much. In general, anything within ~10% of calculations is close enough for solar work.

    Since you have an existing 900 AH battery bank, use it for the next set of calculations. The size of solar array based on back capacity. Using the 5% to 13% current rule of thumb for solar charging:
    • 900 AH * 29 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 1,695 Watt array minimum
    • 900 AH * 29 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 3,390 Watt array nominal
    • 900 AH * 29 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 4,406 Watt array "cost effective maximum"

    The above is based on a "solar only" setup... If your wind is reliable (get significant wind power multiple days per week), you could cut back on the solar panel recommendations.

    Then there is the minimum array to replace the amount of energy used per day. Using PV Watts for Fort McMurry Alberta, fixed array tilted to Latitude (you may need to tilt to vertical if you get lots of snow--better shedding of snow and reflection from snow fields):
    Month      Solar Radiation(kWh/m2/day)
    1      2.57     
    2      3.62     
    3      6.03     
    4      5.48     
    5      5.21     
    6      5.31     
    7      5.48     
    8      4.89     
    9      3.96     
    10      3.78     
    11      2.70     
    12      1.80     
    Year      4.24
    

    Toss the bottom three months (assume wind/generator to make up for poor sun), February at 3.62 hours of sun per day.
    • 150 AH * 25 volts avg batt voltage = 3,750 Watt*Hours per day (DC side of inverter)
    • 3,750 WH per day * 1/0.77 panel+controller derating * 1/0.80 batt eff * 1/3.62 hours of sun = 1,682 Watt array minimum

    Your 740 Watts of solar, during October (this month) would produce around:
    • 740 Watts * 3.78 hours of sun * 0.77 panel+controller derate * 0.80 battery eff * 1/29 volts batt charging = 59 AH @ 24 volts per day

    At this point, I have no idea how much your wind or generator operate. And if the array is fixed tilt at ~57 degrees or something else. But for a solar only system, this is undersized given the assumptions I have made.

    Your thoughts/corrections to my guesses?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: Basic Battery Questions
    rich wrote: »
    We only pull 150 ah while we have been using power tools. thats less than 25% draw on batteries.

    How do you know that you are pulling 150 ah? The reason I ask is that there are several ways to measure/estimate/calculate ah.

    If your battery bank is 900 ah at the 20 ah rate, then your batteries can provide 45 amps for 20 hours. If your power tools draw more than 45 amps DC then you may (depending on how you determine your ah) be over estimating your state of charge.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
Sign In or Register to comment.