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  • offgrid battery questions

    This is a series of questions for all the experts about a power problem that needs solving:

    My colleagues and I are working on an off-grid sustainable construction project. We are not going to be near any source of electricity. For budgetary and logistics reasons, solar panels and generators are not an option. What we do have access to is industrial/forklift batteries. We need to be able to power several tools and possibly some small appliances. Our estimated power use is 5kWh a day. The plan is to charge batteries with this amount of power every day at a project management office in a town near the site. The project will only last from several months to a year, so a particular brand or whether the batteries are new/used is of little concern. We have done just enough research to realize we don’t know enough to know where to begin solving this on our own.

    That being said, here are our questions:

    - Is there a preferred type of battery that works well for being used 12-18 hours at a time? Deep cycle? Golf cart? Forklift?
    - For power tools and lighting equipment, is there a particular voltage the battery needs to be? 12V, 24V, 48V?
    - Our project office will likely be in an industrial park. When looking for space, what electrical specs should the building have?
    - Can most of these large batteries recharge within a 24 hour period?
    - Weight: we will have to haul these batteries to the site daily after charging. Which batteries are light enough to reasonable pack up every day and carry to the site (50 lbs or less)?
    - Wiring: for sustained use, should we wire the batteries as series or parallel?
    - Safety: what are the real dangers of handling the batteries and what precautions can we take to protect ourselves?
    - Does the charger have to be the exact same voltage and Amp-hours (Ah)?
    - What type of inverter do we need? 5kW? Does the type of inverter we use depend on the type of batteries?

    I thank you in advance if you are able to provide any answers or offer advice.

  • #2
    Ummm. Well, to get 5Kwh from a battery bank each day, you're talking about a 10Kwh capacity battery bank (about 500lbs of batteries). Usually it would need to be larger but you say you'll be there less than a year so it would be ok to drain them down to 50%. I'd get 6V batteries if you're going to have to haul them in and out each day and yes, you can recharge them in about 5 hours if you can put 20 amps into them. I'd configure them into a 48V string and buy a 1500W pure sine wave 48V inverter.
    The danger is going to be in assembling and disassembling the battery connections each day. Be sure you use rubber tools or some sort of good insulation on the tools because doing it twice a day greatly increases the odds of a mistake being made where you drop a tool across contacts and create a short circuit.
    1150W, Midnite Classic 200, Cotek PSW, 8 T-605s

    Comment


    • #3
      Well you are playing with FIRE.

      Forklift, golf cart, RV, Marine, Liesure batteries are all hybrids and not true deep cycle. However for your application you do not want Deep Cycle batteries because they are not capable of delivering the very high discharge currents you will need nor can the be charged in 4 or 5 hours.

      If you are looking to use 5 Kwh per day at a minimum will require IMO a 15 Kwh battery because you will be discharging at a high current rate in excess of C/20. A 15 Kwh battery is going to weigh in around 900 pounds and cost a small fortune of around $3000 to $4000.

      You will need to operate at 24 or 48 volts and 15,000 wh / 48 volts = 312 AH or anywhere around 300 AH will work. Or 600 AH at 24 volts. That means a minimum of using 4 to 8-Six Volt Batteries wired in series. Some good industrial batteries in your sizes are Trojan L16P-AC,

      You can use 24 volt like a Crown 24 volt 625 AH Fork Lift battery made from using 4-6 volt batteries. These are really top of the line Fork Lift Batteries with a 5 year warranty and made to be deeply discharged.

      For batteries this size and to be able to charge in 4 to 6 hours is going to mean using a 240 VAC commercial Forklift battery charger and a good 160 amp 24 volt charger.
      MSEE, PE

      Comment


      • #4
        Well, if you have access to forklift batteries, that's the best thing to use. And you will need a very strong trailer to carry them on.

        Going with Sunkings suggestion of 15KWh of batteries, in a 24V battery, that would be 625Ah or in a 48V battery, it would be 300ah.

        If you can get a 48V battery from 300 - 500 ah that would be great. If you are stuck with only a 24v battery, then you need 600-800ah

        Once you decide on a battery, the same shop should be able to provide you with a charger. It will be at least 240V, or maybe 480V 3 phase (we have a 120ah, 48v charger that runs on 480V 3 phase, for our forklift)

        You will need a strong tow vehicle to get the trailer with the battery to and from the job site daily, and you will need to recharge the battery every night. Once a week, check and add distilled water.

        And then you will need an inverter to convert the DC into AC power the tools will use. Tools are Very Power Hungry, and the motors in saws will need a large inverter to start them. You will need good extension cords, 12ga, not cheap 16 ga cords.
        A good 4Kw inverter will weigh about 60 pounds (USA #) A 6Kw inverter a bit more.

        None of this will be cheap.
        If someone forgets to charge the battery at night, you might be able to do some work the next day, but will damage the battery vy deeply discharging it.

        You will need someone qualified to wire up the high power DC and the inverter output AC lines., 6Kw tool starting surges on a 24V system will pull 250A from the batteries, so all crimps need to be hydraulic crimped, or they will be likely to fail. And all the fuses and circuit breakers needed too.

        Not sure why you can't use a conventional generator, but this is what it would take for a battery system
        Powerfab top of pole PV mount (2) | 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

        Comment


        • #5
          Originally posted by Mike90250 View Post
          Not sure why you can't use a conventional generator, but this is what it would take for a battery system
          A genny would be smaller, lighter, cheaper, and work better. . Commercial Industrial grade gennies even have an air compressor for real air powered construction tools.
          MSEE, PE

          Comment


          • #6
            Have been in the same exact boat back in the day when we had
            fixed Locations and 'air conditioned gypsy' satellite Locations going
            at the same time.

            Your less dan 15 bucks per month of electric (at my present
            'country-fied' utility company rate) means little.

            What your peak requirement is at any given time
            (during your daily half bucks worth of electric)
            is the real game.

            Once we know that we can employ the secrets of the ancients
            using the most minimum amount of fuel known to man
            in a hybrid configuration with Legendary portable batteries
            that can snap any winch cable
            and climb any mountain.

            Do some charging at the home base and some at the remote site.
            Make no difference to this system.
            All of it Guaranteed 100% for years except for one cheap
            component.

            No, old Bill isn't talking Lu Lu or Lithium or pro-rated.

            Bill Blake


            Originally posted by offgridnoob View Post
            This is a series of questions for all the experts about a power problem that needs solving:

            My colleagues and I are working on an off-grid sustainable construction project. We are not going to be near any source of electricity. For budgetary and logistics reasons, solar panels and generators are not an option. What we do have access to is industrial/forklift batteries. We need to be able to power several tools and possibly some small appliances. Our estimated power use is 5kWh a day. The plan is to charge batteries with this amount of power every day at a project management office in a town near the site. The project will only last from several months to a year, so a particular brand or whether the batteries are new/used is of little concern. We have done just enough research to realize we don’t know enough to know where to begin solving this on our own.

            That being said, here are our questions:

            - Is there a preferred type of battery that works well for being used 12-18 hours at a time? Deep cycle? Golf cart? Forklift?
            - For power tools and lighting equipment, is there a particular voltage the battery needs to be? 12V, 24V, 48V?
            - Our project office will likely be in an industrial park. When looking for space, what electrical specs should the building have?
            - Can most of these large batteries recharge within a 24 hour period?
            - Weight: we will have to haul these batteries to the site daily after charging. Which batteries are light enough to reasonable pack up every day and carry to the site (50 lbs or less)?
            - Wiring: for sustained use, should we wire the batteries as series or parallel?
            - Safety: what are the real dangers of handling the batteries and what precautions can we take to protect ourselves?
            - Does the charger have to be the exact same voltage and Amp-hours (Ah)?
            - What type of inverter do we need? 5kW? Does the type of inverter we use depend on the type of batteries?

            I thank you in advance if you are able to provide any answers or offer advice.

            Comment

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