Modified Sine wave Inverters differ from True Sine Wave Inverters in the way that the waveform output does not even look like a Sine wave inverter, it however have the same frequency and approximate same voltage values.
Fig 1 Output Wave for difference between a Pure Sine Wave and a Modified Sine Wave Inverter
You would often hear somebody tell you that you need a true sine wave power inverter to operate your computer…this is nonsense…true sine wave power inverters have their place, but the higher price you pay for them compared to modified sine wave power inverters must also be justified..and Is not always justifiable.
Ok, so where and why do we use Modified Sine wave power inverters?
Modified sine wave power inverters usually fall in the lower price range. Within the range of Modified sine wave power inverters, you get various quality, Good, Lower and really poor quality. Most of the “cheap & Nasty” units have a pure Square wave output and the output voltage is not regulated. This the output voltage can vary from 180V AC to 300V AC as the battery voltage vary.
We have recently found that certain TV’s,computers and coffee Machines do not operate with modified Sine wave inverters. They do not get damage, they simply do not switch on and the control software protect the unit.. This seem to becoming a bigger phenomena
So what is the reasons not to always use Modified Sine wave inverter , as they are cheaper ?
As mentioned earlier, you get quality and QUALITY in the range of modified Sine wave inverters, tests which we conducted our selves has shown
Motors, ie fridges swimming pool pumps etc run a bit warmer on mod sine (advanced Mod sine units has overcome this problem)
They do not start as easy as with Sine wave inverters, Units have to be overrated
Anything with a big capacitor as input phase SUCH as Fluorescent lamps, does not work on Modified Sine waveform
Small CFL lamps 8W,11W 18 W etc, have a reduced life time as the input capacitors damage with time
General Cell chargers , Camera chargers etc, seem to work fine, However we can make NO comment if it have an effect of reducing the lifetime of same…as it has the same input phase as CFL lamps, in my opinion in the long term it could be damaging- but the life time these days of Celphones and chargers, versus that time is probably of no concern
Keeping the above in mind, one need to consider that Most electronic equipment which have a pre power source, this is Computers, Laptops, MOST cell phone chargers, small electronic ballast lights... tills…all of this equipment, take your power as supplied by Eskom or a power inverter and rectify it…after it is rectified it becomes DC and then the DC is converted again to another level of DC …. So... if the power coming in is DC, AC or modified sine wave…it just doesn’t matter as it gets rectified to DC in anyway!!! So if you really just want to run a Laptop. You don’t need atrue sine wave inverterand if it is only occasionally the less of a problem.
Most UPS power backup systems, that act as backup power for hundreds of computers ARE NOT true sine wave power inverters they are indeed modified sine wave power inverters.
Further to this, certain equipment using “universal motors” such as vacuum cleaners and roof Fans, drilling machines…can operate just as well from DC as from AC and/or modified sine wave…however there are exclusions to this rule!!!
Some motors such as roof or ceiling fans (fans to keep your house cool), run well on modified sine wave inverters ….but they are noisy!! So too are some other motors…the noisy sound comes from the high frequency harmonics created by modified sine wave inverters... so yes it runs but sounds terrible. .and that buzzing noise is very irritating when you try to sleep.
Some chargers which use, thyristor controls at the input or which have “charge rating options” do need sine wave inverter outputs.
I wrote some articles earlier on the affect that Modified Sine wave inverters , it is a bit technical and perhaps this is not the forum for same, but if you interested please read attached:
Items which we would suggest not to run from modified Sine Wave inverter:
High precision chargers
Swimming pool pump
Fridges fitted with compressors
Fridge / Freezer
Camera equipment which use the Line signal for sync
Timing devices such as bed alarm clock which use the power signal as a timing base
Tropical fish tank pumps
If you are uncertain, please contact us for any further suggestions. We will be happy to assist you in your making the correct choice of power inverter.
Modified Sine Wave inverters are ideal for the smaller to Mobile kind of application, use for occasional backup , or intermediate power supply requirements. We would not suggest same for permanent fixed Solar system applications. Ideal for :
4x4 occasional power supply
Driving Laptops from Cars
Recharging occasional cell phone and cameras
Mobile Home applications etc
Fig 2 1500W Modified Sine Wave Inverter
Please feel free to contact us for any information or advice concerning inverters [email protected]
Copyright Dr Gawie van der Merwe , PlanMyPower PTY Ltd
Table 1- List of Omnipower Modified Sine Wave Inverters