Batteries Choices

andy300zandy300z Solar Expert Posts: 39
Hello
I am in the process of purchasing batteries and we all know golf cart and forklift batteries are the best for solar projects.Due to budget constraint i am thinking
about getting the following deep cycle batteries

Costco: Kirkland Brand group24 85 amp hour $65 with 3yr warranty

Walmart : Everstart group 27 105 amp hour $70 with 2yr warranty

I know that you should always try to get True deep cycle battery but if i wait to get the funds it will take forever.

Any suggestions on the above choices.

Thanks

Comments

  • icarusicarus Solar Expert Posts: 5,355 ✭✭✭✭
    Re: Batteries Choices

    The suggestion is to avoid "ready, fire, aim!" Don't buy any batteries until you have defined your expected loads, and defined how you expect to recharge them on an ongoing basis.

    There is no real point in spelling out a number of hypothetical scenarios without knowing your intentions. In addition, the heart of any battery based system, is the batteries, and the balance between the loads the expected depth of discharge and the charging capacity will really decide for you. There is often false economy in buying a cheaper set because they are cheaper.

    Good luck, welcome to the forum, and let us know what it is you are trying to achieve, and there are those here who will proffer an informed opinion!

    Tony
  • andy300zandy300z Solar Expert Posts: 39
    Re: Batteries Choices

    I am trying to power up my home office which runs about in total of 125watts everyday. I am purchasing a morningstar 300w pure sine which will give me enough power to run the office and has a low stanby power consumption.
    I also have a sump pump which i need to run when i loose grid power or my basement will get flooded. The pump uses about 800watts. I am planning to buy 4 batteries for now which will give me appx 400 amp hours.
    Thanks
  • BB.BB. Super Moderators, Administrators Posts: 29,717 admin
    Re: Batteries Choices

    Get a Kill-a-Watt meter (if you don't have one)...

    125 watts * 1 hour or * 10 hours per day--big difference.

    One of the difficulties with Costco and Walmart batteries is they can change vendors every few years. So, if somebody said their 5 year old Mega-Mart batteries are still working great--It is not a guarantee that the batteries will even be made by the same company today.

    Also, sizing a battery bank is very dependent on how much charging ability you have... Solar, grid power, generator backup (probably not an issue in this case) all are affected by the sizing of your battery bank.

    As a start--perhaps get enough battery to power your office with about 25% power use per day (2 days of no-sun and 50% maximum discharge for long life).

    For example if you are planning on a 400 AH 12 volt battery bank, that would indicate:
    • 400 AH * 12 volts * 25% daily use * 0.85 inverter efficiency = 1,020 Watt*Hours per day
    • 1,020 WH per day / 125 watt constant AC load = 8.16 hours per day load
    For the AC Charger--would recommend around 5-13% (larger is OK--just don't pay a bunch of money for next size up charger):
    • 400 AH * 5% = 20 Amp minimum
    • 400 AH * 13% = 52 Amp maximum (useful)
    And for solar panels--if you intend to charge the battery bank with them:
    • 400 AH * 14.5 volts charging * 1/0.77 derating * 5% = 377 watts minimum
    • 400 AH * 14.5 volts charging * 1/0.77 derating * 13% = 979 watts cost effective maximum
    Assume sunny weather operation is 4-5 hours of sun or better per day:
    • 377 watts * 0.52 system derating * 4 hours sun = 784 WH per day
    • 979 watts * 0.52 system derating * 4 hours sun = 2,032 WH per day
    Or if you want to use 1,020 WH per day (from first calculation):
    • 1,020 WH per day * 1/0.52 eff * 1/4 hours per day = 490 Watts of solar panels (4 hours of sun per day)
    -Bill

    PS: Add that there is nothing wrong with buying an inexpensive set of batteries first--Most people make a few major mistakes with their first bank and killing the batteries before their time... It does not hurt to make your first mistakes with a "training bank".
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • icarusicarus Solar Expert Posts: 5,355 ✭✭✭✭
    Re: Batteries Choices
    andy300z wrote: »
    I am trying to power up my home office which runs about in total of 125watts everyday. I am purchasing a morningstar 300w pure sine which will give me enough power to run the office and has a low stanby power consumption.
    I also have a sump pump which i need to run when i loose grid power or my basement will get flooded. The pump uses about 800watts. I am planning to buy 4 batteries for now which will give me appx 400 amp hours.
    Thanks

    Sorry to beat this horse again, but loading means almost nothing unless you have a time element. For example, your 125 watts for one hour would be 125 watt/hours! The same 125 for 10 hours would be 1.25 kwh. Until you can define the loads, and their estimated durations, it is difficult to suggest a battery. As Bill suggests, buy a ~$15 Kill-A-Watt meter, and accurately log your loads .

    Good luck, and keep in touch,

    Tony
  • dhsoladhsola Solar Expert Posts: 38
    Re: Batteries Choices

    Yes, what icarus and BB said!

    But just to give you an idea of what your looking at useage-wise, I have two of the Kirkland 115 Ah batteries with two Interstate 105 Ah batteries under an inexpensive 10 amp PWM controller, under an inadequate 100 watt solar panel. These go through an Xantrex Pro-Watt SW 600 watt inverter. I can run my laptop from this setup for hours but the desktop computer/LCD monitor (170-200 watts) with no peripherals, will drop the battery voltage down from 13.1 volts to 12.4 in about 2-3 hours or less depending on how hard I run the quad-core CPU and how often I use the Operating Systems "sleep mode."

    I've only had the Kirkland batteries for a couple months, but they seem to be OK for a box-store battery.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Batteries Choices

    13.1v to 12.4v sounds about right. you are showing a 13.1v surface charge as the batteries are more likely to be about 12.6v or 12.7v after a rest period of 3 or 4 hours. remember that 170-200w is a great deal of current when talking about 12v. 185w/12v=15.4a. also note that those batteries should not be intermixed as only like batteries should be mixed and preferably of the same age and quality so all of your batteries are as good as the worst battery in the bunch.
  • dhsoladhsola Solar Expert Posts: 38
    Re: Batteries Choices
    niel wrote: »
    13.1v to 12.4v sounds about right. you are showing a 13.1v surface charge as the batteries are more likely to be about 12.6v or 12.7v after a rest period of 3 or 4 hours. remember that 170-200w is a great deal of current when talking about 12v. 185w/12v=15.4a. also note that those batteries should not be intermixed as only like batteries should be mixed and preferably of the same age and quality so all of your batteries are as good as the worst battery in the bunch.

    Yes, agreed. This little setup is basically made up of left-over, hand-me-down parts. I use it as often as possible to take loads off the main system and 'because it's there.' Hopefully, andy300z can get a quick-pic of just how much and how quickly computer stuff can pull juice from a small battery setup..

    My 20 year old, 900w laser printer would never work on this setup.. just kidding;)
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