Some useful questions to ask yourself to determine if you need a pure sine wave inverter include: 1. Does the device or appliance use a motor? 2. Is the device a delicate piece of medical equipment? 3. Does the device or appliance use a rectifier? 4. Can the device be powered by a DC. A modified sine wave inverter will work for most situations, but there are some cases where it might cause damage or be less efficient. Devices that use AC motors, like refrigerators,. If your electronic devices use rectifiers to convert AC to DC, you probably don't need a pure sine wave inverter. Don't be mistaken, it will still work just fine with these devices.