Pure sine wave or Modified Sine Wave – that is the question and I’m sure many people have differing views.  I don’t want to get into an argument on benefits and differences of either version, each to their own as always.  I just want to relay my personal experiences over the past 15 years of using a variety of Inverters and point out my rationale for choosing my particular type.   I’ve also included a statement from a well known supplier to justify my choice.

So first of all – what is the difference?

True or Pure Sine Wave

Pure Sine wave is the same as the power you have in your home. It is very clean and is the optimum for performance.  Therefore, appliances such as TVs, computers and stereos run cleaner and easier. Also, Pure Sine wave generates less heat than other waveforms.

Quasi or Modified Sine wave

Modified Sine wave is an output that tries to imitate pure sine waves but comes up a little short, its not as clean as Pure Sine Wave.   Nevertheless, modified sine wave inverters have their advantages.   The main downside to modified sine wave output is slight interference. This interference can be seen on some older televisions and computers. It will not cause any damage, but can be a little annoying. The upside to modified sine wave inverters is they will run most appliances, and are very affordable.   Modified sine wave inverters are great to run appliances and equipment such as power tools, non-digital microwave oven, lights, and other motor driven loads.  The bottom line is that over the past few years electrical appliances now use switch mode power supplies in there design that are a lot more tolerant than of old and work fine with Modified Sine Wave Inverters.

A well known supplier of electrical equipment says:-

“Sterling has invested in a new range of quasi-sine inverters because they are smaller, lower cost, offer better performance, are more efficient and more reliable than sine-wave. We at Sterling have always found the quasi-sinewave inverter more than adequate for general requirements in boats and vehicles. There is still the odd appliance, such as washing machines, where quasi-sinewave inverters simply do not work, but all in all they do a great job – especially considering their cost.   It’s still usually a lot cheaper to replace a £ 35 microwave to a different model which will work rather than spend £ 700 on a sine wave model to make it work”

What size inverter do I need?

This depends on what you want to operate. If you want to run a 600-watt drill, a 150-watt inverter will not do the job. When choosing an inverter determine what you want to run and then get the inverter that delivers the appropriate power you need. Most appliances have their power rating printed on them or their packaging.   Remember many electric motors will consume more power on start up than when running.  Most Inverters will quote two figures one is the constant running value and the other is the peak load value.  peak load is the spike or start up watts that the inverter will take without switching off.  So in our case we have a 2500W inverter with a peak value of 4000W.  This means during the initial start up period our inverter will provide a current up to 4000W for a brief period before cutting out.  In general terms this period is sufficient to allow electric motors start up and settle down to their normal running wattage.

A simple equation to help determine the power you need is as follows:

Volts (230 or 240) x Amps = Wattage

Now all inverters consume a little power themselves, after all you don’t get anything for nothing in this world, so inverters will run at around 90-95% efficiency meaning when switched on but not powering anything they will drain amps from your battery(s).  The larger the inverter the more power they will consume.  For example our 2500W inverter consumes 0.2amps just on standby and that is quite good.  Many will consume up to 0.5 amp on standby.  leaving it switched on for 24 hrs ours will consume 4.8amps, some could consume up to 12 amps so remember to switch it off when not in use.

Most inverters have built in safeguards such as low voltage cutoff meaning that the inverter will shut itself off if your battery gets low.  Other safeguards are polarity cutoff, overheating cutoff and overload cutoff.  Many of the larger inverters have remote control switches with LED lights so you can tell if the unit is switched on or off.  In our experience a remote control switch is essential as many if not all inverters are hidden away and it is easy to forget whether they are on or off.

Nobody will argue that a pure sine wave is better than a modified sine wave, however just bear this in mind:-

Modified Sine Wave inverters are very much cheaper than Pure Sine Wave inverters – by a factor of up to 4:1

Most electrical equipment is more tolerant these days than a few years ago so can cope with the variations in power – as anyone living in an area that suffers from poor distribution will testify (dimming lights, resting of UPS units etc.)

There are few appliances these days that need a Pure Sine Wave and are usually limited to sensitive medical equipment and certain microwave ovens.  We have owned Modified Sine Wave inverters now for over 15 years and never had a single problem.  The biggest issues always seem to be that folks buy a 200W inverter and complain when their 3000W kettle won’t work.  Others criticise inverters because their battery is always flat (single 110AH) – after watching a 240volt tv for 6 + hours and leaving the inverter on 24/7 then boiling the low watt kettle (850W) three of four times a day.  I mean a low watt kettle is the answer as they don’t use any power – right?????? – I don’t think so.

Remember these golden rules:  Inverters are only part of the set up – available battery power is also essential.  Many tv’s these days will run on 12 volts so there is no need to turn on the inverter so you can use the 240 volt adaptor to power the tv.  Always turn the inverter off when not in use.  Never overload the inverter and if you are planning on going wild camping then be frugal with battery power as a whole.


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