• Gel batteries vs liquid (lead-acid). What are the pros and cons of each?

    GEL BATTERIES are rechargeable valve-regulated lead-acid with a gelified electrolyte. They are maintenace free, so no need to keep them upright. As they are sealed there is no risk of spillage or evaporation. They are more resistant to extremes of temperature, shock or vibration. They require a stabilised, regulated charging system. They are slower to charge and must never be over-charged. They have a lower capacity for given dimensions and have less ability to dissipate heat. 

    LEAD-ACID BATTERIES are fine with a conventional charging system and are less expensive for any given capacity. They are excellent at dissipating heat. They need to be kept upright and need the electrolyte (water) to be topped up from time to time. 

  • How is Endurance calculated?

                   ENDURANCE (hrs) = CAPACITY (Ah) x DC VOLTAGE

                                                          CONTINUOUS POWER (W)

        Capacity is a measure of the charge (available energy) stored in a battery.

  • What does an inverter-charger do?

    While mains power is on, the inverter-charger charges the battery (or batteries). When mains power fails the inverter-charger instantly switches to drawing power from the batteries and converting that power into AC power. Thus any appliances connected to the system will have a continuous supply and will not be affected. For example computers will continue to run with no data loss, and sensitive medical equipment will operate perfectly. 

  • What is a deep cycle battery?

    A deep-cycle battery is a lead-acid battery designed to be regularly deeply discharged using most of its capacity. A deep-cycle battery is designed to discharge between 50% and 80% of its capacity, depending on the manufacturer and the construction of the battery. Although these batteries can be cycled down to a 20% charge, the best lifespan vs cost method is to keep the average cycle at about 50% discharge. There is a direct correlation between the depth of discharge of the battery, and the number of charge and discharge cycles it can perform.

  • What is load shedding?

    Load shedding is the process of switching off all but the essential items in order to maximise the endurance time of the most essential equipment. 

    So, switch off such things as oven, air conditioning, iron and electric heater. Only heat a kettle intermittently. 

  • What is the correct way to connect my UPS inverter/charger to the batteries?

    Here is the diagram for connecting two 12V batteries connected in series (to give 24V).

    You will need the connection marked “A”.


    Two battery connection for UPS system


    This diagram shows how to connect two banks of 2 x 12V batteries in parallel, connected in series.

    You will need the connection marked “A”.

    Four battery connection for UPS system

  • What is the difference between a lead-acid battery and a calcium battery?

    Both of these types of batteries are lead-acid. When Calcium is added to the battery plates it improves the performance of the battery and there is less internal gassing of the battery. Therefore the battery terminals require little or no maintenance.

  • What is the difference between pure sine wave and modified sine wave inverters?

    Alternating current (AC) has a continuously varying voltage that swings from positive to negative. This has great advantages in power transmission over long distances. Power from your power company is carefully regulated to be a perfect sine wave, because that is what naturally comes out of a generator. 

    On the other hand, a pure sine wave is expensive to make in an inverter. The most inexpensive way to make AC is to switch it on and off – a square wave. A modified sine wave is designed to simulate a sine wave in the most important respects so that it will work for most appliances. It consists of a flat plateau of positive voltage, dropping abruptly to zero for a while, then dropping again to a flat plateau of negative voltage, back to zero for a while, then returning to the positive voltage. 

  • What is the meaning of Ah?

    Ah stands for Ampere-Hour and is a measure for battery capacity. It is calculated by multiplying the current flow in amperes by the time in hours of discharge. (Example: A battery which delivers 10 amperes for 15 hours delivers 10 x 15 = 150 Ah).

  • Where can I find out more about self-reliance?

    There are many sources of information about self reliance, sometimes called ‘prepping’. 

    A particularly good site is found here. 

  • Which should I consider, a pure sine wave or a modified sine wave inverter?

    The following gadgets work well with a modified sine wave: computers, motor-driven appliances, toasters, coffee makers, most stereos, ink jet printers, refrigerators, TV’s, VCR’s, many microwave ovens, etc. 

    Appliances that are known to have problems with the modified sine wave are some digital clocks, some battery chargers, light dimmers, some battery operated gadgets that recharge in an AC receptacle, some chargers for hand tools. In the case of hand tools, the problem chargers usually have a warning label stating that dangerous voltages are present at the battery terminals when charging. 

  • Why do I need to consider an uninterruptible supply system (UPS)?

    Due to a variety of factors mains electricity supply is getting less and less reliable.  While the national demand for electricity is increasing steadily, the generation capacity is not keeping pace.  The supply of the fossil-fuels required by the power stations is also getting less certain.  As fuel prices continue to rise the reserve stockpiles of fuel held by the power companies is being reduced to critically low levels.  Also the incidence of extreme weather events is increasing, and these too, often result in power cuts (e.g. winter snow storms of 2011 and 2012, hurricane force winds of Oct 2013). 

    There is more information Read this article. 

  • What I’m trying to do is set up a backup power system for my house in the event of a mains power cut. Ideally a seamless automatic switch-over of some sort. Maximum power requirement would be about 5225W. Am I correct that your Heavy Duty Kit can do this?

    Yes.  The continuous rated power for the Heavy Duty kit is 3000W, peak power is 6000W.  It is very unlikely that you would have everything switched on when the power failed, but even if you were drawing 5000W+ you would do some load-shedding in the first few minutes.  The inverter can cope with 3000W indefinitely as long as the batteries hold out.  The 6000W limit is constrained by the possibility of it overheating so while it can produce that output power it is only recommended for a few minutes.

  • How is your UPS system connected to the house’s mains circuit? Would I need an automatic transfer switch (ATS)?

    You do not need an ATS as the inverter acts as an ATS itself.  Our recommended method is to install a second consumer unit, for all the circuits that you want to be uninterruptible, i.e. lights, plug sockets, central heating boiler,  whilst the high power appliances (cooker, immersion heaters, power showers etc) stay on the original CU.  The uninterruptable CU is powered via the inverter.

  • Can more than four 110Ah batteries be attached to the inverter-charger to extend endurance?

    Yes, you can attach as many as you feel are required.  As you add more they need to be in parallel to maintain the voltage. (Better to use a higher voltage DC input i.e. 48V which reduces the DC current and hence reduces the cabling size required.)

  • Do you know if a Sky box works with a modified sine wave inverter-charger?

    Yes, they are essentially the same as computers and are tolerant of modified sine wave.

  • Do laptops generally work OK with modified sine wave inverter-chargers?


  • What are the advantages of a 24V versus 12V inverter-charger?

    If you are intending to utilise four or more batteries you are best advised to use a higher DC current inverter.  This enables the batteries to be connected in series and this keeps the current lower.

  • We would like to site a UPS system in the garage next to the fuse box. Is there any way to tell from inside the house that the system has switched to battery power?

    The lights will flicker on switch-over.  Then you can check any appliance on the standard consumer unit.

  • What’s your typical lead time to deliver a UPS Kit?

    Delivery of the inverter-charger usually takes around three weeks as it is made to order. The batteries are usually delivered within a few days.

  • I want to put RCDs on the inverter output. I have tried with standard ones but they keep tripping. What type do I need?
    There are three common types of RCD (ELCB):

        Type A   - Detects AC and pulsating DC fault currents,  - This type can only be used with single phase drives.

        Type B   - Detects AC, pulsating DC and smooth DC fault currents - This type must be used with three phase drives.

        Type AC - Detects AC fault currents only - This type should never be used with an Inverter.

    For use with an inverter Type A should be used.

  • I’m looking to buy the 2000W UPS set up. How many hours does it take to fully charge the battery. Is it possible to use the gel batteries with this set up?
    The charge time for the batteries depends how many batteries are connected.  Our 2000W kit uses 2 large batteries with a total capacity of 220 Amp hours. The max charge current is 8A.  So if these were completely discharged it would take about a day to recharge them completely.
    In practice however it is very rare that they would be completely discharged.  With normal use if the battery power were used for 4 hours it would normally take a similar period to recharge.
    The inverter/charger has options to select which type of battery is being used so that the charging pattern is optimised for the battery type.  Gel batteries are one of the types provided for. So yes these can be used.
  • What size UPS kit would I need for 2 or 3 chest freezers?

    A modern chest freezer will have a power consumption of less than 100 W (when the compressor is running) and should consume less than 1 kWh per day.  Our basic 600 W inverter/charger would be sufficient to power 3 freezers.  The battery would support 5 hours continuous running at 300 W, but would probably be good enough to keep the freezers running for 8-10 hours (since the motors do not run continuously).  If you need a back up to last longer just add additional batteries.



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