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Inverters

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    Inverters

    I'm planning on getting an inverter, to hook up to the car, as an emergency power supply. Primarily for mains LED table light, TV, laptop. And possibly the fridge/freezer and Oil C/H system. I prefer this idea to getting a generator. (Most generators use an inverter to produce 240v anyway.)

    If the electricity was only out for a couple of hours or so, then I'd just run it off the car battery, and recharge the battery afterwards. If it was out for an extended period of time, then I'd leave the engine idling so the alternator keeps the battery charged.

    I bought a cheap one off eBay a few years ago but it went kaput after a few hours of use.

    1) can anyone recommend a reliable make of inverter?
    2) anything else I should consider eg. is pure sine wave necessary for powering electronic devices?
    Scoots still says that Apr 2020 didn't mark the start of a new stock bull market.

    #2
    You probably need to speak to an electrical/electronic engineer, but check the load you require - freezers can draw a bit.
    If you’re planning to run the car engine to generate, that’s one thing, if you’re hoping just to use the car battery, I don’t think you’ll get very long - again, speak to an IEEE type person, they should know
    As for pure sine wave, I think a lot of that is marketing. Laptops tend to have universal voltage transformers which can cope with a wide range, and there’s a battery in your laptop too. Having done some safaris where a generator comes on for a couple of hours every night, and the load on it varies (as does the quality of the output), I’ve never had an issue with phones, cameras, laptops, etc.

    But back to the start, I think your issues are going to be related to the load.
    …Maybe we ain’t that young anymore

    Comment


      #3
      Here you go:

      https://www.motorhomefun.co.uk/forum...verter.224308/

      The electronics are one thing, the fridge is something else.

      I'm not sure motors like modified sinewave:

      https://www.lifewire.com/modified-si...he%20equipment.

      If you deep discharge a carbattery it won't be at all happy.

      A leisure battery on the other hand is designed for this.
      Last edited by DoctorStrangelove; 18 September 2022, 11:45.
      When the fun stops, STOP.

      Comment


        #4
        Considerations ...

        Firstly, the battery in the car is designed to start the car, it will probably not be a deep cycle battery for sustained demand and is likely a relatively low capacity battery. Unless there is a fancy charging system in the car, the output of the alternator at idle speed won't keep up with the demand.

        Cabling. Assuming that the inverter is near the car, as would be needed for volt drop on the 12V side, then you'll need to run cables to the things your want to power up from the inverter. This could result in long and untidy cables.

        Safety. Earthing and circuit protection as per regulations.

        Power budget. Need to determine the total load and running time to estimate the battery Ah needed. Also ensure that the inverter can cope with motor starting current.

        Have you come across these Power Station gadgets?
        They provide charger, battery and inverter in a semi-portable package. Some can be enhanced with solar panels or small generators. This may better suit the requirement and you could speak to a manufacturer about one that would run the appliances you're considering. These are quite expensive, reflecting the high-tech batteries used.

        Examples. https://www.techradar.com/best/portable-power-stations
        Last edited by Protagoras; 18 September 2022, 18:15.

        Comment


          #5
          TV + LED table light + laptop < 100W

          Which is 8A @ 12V. Should be able to run these off just the car battery for a couple of hours.

          Anything extra sounds like it could be a problem, even with the engine idling.

          ----------

          We're on private water which would have been nice to keep going but the borehole pump is 1kW, and that sounds like a non-starter.
          Scoots still says that Apr 2020 didn't mark the start of a new stock bull market.

          Comment


            #6
            After some "research" it appears that the starting current of a 1kW single phase motor is 3x the run current so you'd need a 3kW inverter just to start the thing.

            Having perused various Septic offgrid sites in the past, they seem to go for 5kW and 6kW petrol/propane generators, presumably since what comes out of the alternator is something rather closer to a sinewave than what comes out of your average modified sine inverter.

            If I could be arsed, I'd fire up one or other of the generators in the shed & stick a scope on the output to find out.
            Last edited by DoctorStrangelove; 18 September 2022, 22:17.
            When the fun stops, STOP.

            Comment


              #7
              Originally posted by DealorNoDeal View Post
              TV + LED table light + laptop < 100W
              Are you sure (you’ve not mentioned make/model)?
              Are you reading the power usage of the laptop, or the power of the transformer.
              Also, you’ve gone from 100W at 230V AC to 100W at 12V DC and assumed 100% efficiency

              Speak to a qualified electrical engineer.
              …Maybe we ain’t that young anymore

              Comment


                #8
                Originally posted by WTFH View Post

                Also, you’ve gone from 100W at 230V AC to 100W at 12V DC and assumed 100% efficiency
                + 1

                Inverter efficiency varies with load, and could be very low for a lightly loaded inverter. On the other hand, a well matched high-quality inverter could be over 90% efficient. The inverter manufacturer should have a chart of efficiency vs load. The requirement to run a fridge motor is a complication owing to the high starting current, as noted above.

                PS - Writing as someone who doesn't have a TV, I was interested to see just how little energy a modern TV may use. https://ecocostsavings.com/tv-wattage/

                Last edited by Protagoras; 18 September 2022, 23:36.

                Comment


                  #9
                  Originally posted by WTFH View Post

                  Are you sure (you’ve not mentioned make/model)?
                  TV is 52W. Table lamp is 7W. Laptop charger is 65W (max) but I'd expect it to draw a lot less than this, especially as the battery would already be fully charged (laptop is always plugged in).
                  Scoots still says that Apr 2020 didn't mark the start of a new stock bull market.

                  Comment


                    #10
                    Originally posted by DoctorStrangelove View Post
                    After some "research" it appears that the starting current of a 1kW single phase motor is 3x the run current so you'd need a 3kW inverter just to start the thing.

                    Having perused various Septic offgrid sites in the past, they seem to go for 5kW and 6kW petrol/propane generators, presumably since what comes out of the alternator is something rather closer to a sinewave than what comes out of your average modified sine inverter.

                    If I could be arsed, I'd fire up one or other of the generators in the shed & stick a scope on the output to find out.
                    I think we'll stick with the bottled water.
                    Scoots still says that Apr 2020 didn't mark the start of a new stock bull market.

                    Comment

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