Energy Matters

WIND ENERGY & SOLAR POWER AUSTRALIA
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A guide to power inverters

In the context of renewable energy, an inverter is a device that will convert  DC battery voltage into mains type AC power.

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Most medium to large scale solar power systems are designed to power everything from mains type AC voltages "inverted" from the DC battery bank. The advantage this gives us is that we can purchase conventional appliances from the local electrical store. For example, an energy efficient light globe can be somewhat expensive in a 12 Volt DC version. Having a 24 or 48 volt lighting system makes finding a suitable light bulb even more difficult. 

If you get all your power from an inverter you can scoot off to your electrical store and choose from a great selection of super efficient, low power consumption light globes that will cost a fraction the price of anything that is only DC rated.

• Inverter ratings
• Modified sine wave and true sine wave inverters compared
• Modified sine wave inverters
• Sine wave inverters
• Converting a modified sine wave inverter into a true sine wave inverter?
• Inverter Tips

Inverter ratings

The three ratings that you should look at when buying an inverter are:

1. Continuous Rating: This is the amount of power you could expect to use continuously without the inverter overheating and shutting down.
   
   
2. Half Hour Rating: This is handy as the continuous rating may be too low to run a high energy consumption power tool or appliance, however if the appliance was only to be used occasionally then the half hour rating may well suffice.
   
   
3. Surge Rating: A high surge is required to start some appliances and once running they may need considerably less power to keep functioning. The inverter must be able to hold its surge rating for at least 5 seconds. TVs and refrigerators are examples of items that require only relatively low power once running, but require a high surge to start.

Modified sine wave and true sine wave inverters compared

There are basically two types of inverters: modified sine wave (aka modified square wave) and true sine wave. The differences between these two types of inverters are subtle but significant in the way they operate.

Examples of modified "sine" wave vs  true sine wave:

Modified sine wave inverters

A modified sine wave inverter can adequately power some household appliances and power tools. It is cheaper, but may present certain compromises with some loads such as computers, microwave ovens, laser printers, clocks and cordless tool chargers. Virtually all low cost inverters are "modified sine wave". A modified sine wave is easier and cheaper to produce than a sine wave inverter. 

It is also a fact that cheaper modified sine wave inverters have given this type of inverter a bad name. These low cost inverters are generally available from electrical stores, hardware stores, automotive store and electronic suppliers. They usually lack many features such as auto-start or any type of tweaking ability. The devices are usually about 70% efficient, so expect some significant power losses if you are using a modified sine wave inverter in your system. We do not sell such devices.

Sine wave inverters

A sine wave inverter is designed to replicate and even improve the quality of electricity supplied by utility companies. To operate higher-end electronic equipment, a sine wave inverter is recommended. Efficiency has reached up to about 94% and the electricity from these devices is of a higher quality than grid power almost anywhere in the world. We only sell this kind of inverter.

A high quality inverter will include:

• An auto-start system. An auto start allows an inverter to switch to a low power consumption standby state when nothing is connected and turned on. This will save you a lot of manual switching and/or wasted power
• Tweaking ability. An ability to adjust parameters such as auto-start and battery depth of discharge is also helpful.
• High quality heavy-duty power transformer. A heavy inverter usually means a high quality heavy-duty power transformer.

Converting a modified sine wave inverter into a true sine wave inverter

If you have an modified sine wave inverter and suspect you need a true sine wave inverter, please note there is no ‘filter’ or ‘retrofit’ you can apply to the output of an modified sine wave inverter to ‘clean up the output’ or ‘turn it into true sine wave’.

Inverter Tips:

In general, any device that senses either voltage peaks or zero crossings could have problems when running from modified sine wave.  Devices such as these should be run from true sine wave inverters.  

Ham radio and CB radio operators may notice RF noise from modified sine wave inverters; in that case do not run the radio and the inverter at the same time. Electronics that modulate RF (radio frequency) signals on the AC line will not work and may be damaged. You may notice hum or buzz in the audio of TV’s, radios and satellite systems used with modified sine wave inverters.  Audiophiles or professionals using sophisticated audio, remote measurement, surveillance or telemetry equipment should use true sine wave.

Examples of problem devices are motor speed controllers employing triacs, and some small battery rechargers that do not incorporate a transformer between the utility power and the load.  To help you visualize this, if there isn’t a ‘wall wart’ between the battery charger (or the battery in the device) and the AC plug, don’t use modified sine wave. 

Please note two other common problem loads, electric shavers and emergency flashlights.  Both of these items have batteries in them but connect directly into the wall to charge, without an external transformer.  Don’t use items like these with an modified sine wave inverter.  If you do use an modified sine wave inverter with a transformer-less charger, your product will likely be damaged.   

Garage door openers, laser printers and large strobes used in photography have all been reported as trouble loads for modified sine wave inverters; they either don’t work at all or stop working entirely, so don’t take a chance – use true sine wave.

As a general rule, products operating through an AC adapter will work fine from an modified sine wave inverter.  These include laptops and cell phone chargers, video games, camcorder and digital camera chargers.  Televisions generally work well; some VCR’s with inexpensive power supplies run poorly. Consider switching to another brand of VCR in that case.   

A potential solution for RV’ers or off-grid cottagers is to purchase our smallest true sine wave inverter to run TV, VCR and audio equipment, and a larger modified sine wave inverter (such as the XPower 1750 Plus) for the coffee maker, hair dryer and microwave.

Check out our range of inverters you can buy online and if you have any questions, please email or call our friendly team on 1300 727 151