Emergency Power Options

Emergency Power Options
Logan Storehouse ERC Net Training Topic for May 20, 2012
Rick Hughes, K7YPR

Gas powered generators have been the mainstay of emergency power particularly for heavier electrical loads sustained over an extended length of time.  There are alternatives to this more traditional form of backup power for applications requiring smaller amounts of power or intermittent moderate loads.   One such option is comprised of a heavy-duty deep cycle battery and inverter which provide convenient AC power for various applications.  These integrated power packs facilitate indoor use and can easily move from room to room in contrast to the traditional gas powered generator which must remain outside.

The Duracell PowerPack 600 [1] was shown at the January Share Fair. There are other manufacturers such as Black & Decker, Stanley and Xantrex who make similar products.  Some target automotive roadside emergency applications and may include air compressors and jumper cables.  Xantrex offers a 1500 Watt version with a retractable handle and airport style rollers.  The Duracell product is rated at 600 Watts, includes an AM-FM radio, utility light and jumper cables.

At the Share Fair, a very good question was raised concerning the quality of the AC power generated by the power pack inverters.  The Duracell’s inverter generates what’s termed a modified sine wave AC output.  Some manufacturers may use the expression “step sine wave approximation” which essentially means the same thing.  Most of the lower cost inverters which convert 12 Volts DC to 120 Volts AC are of this type and do not generate a pure sine wave output which looks the same as the wall outlet in your house.  These modified sine wave inverters are also more efficient, smaller, lighter and cheaper.  Virtually all home UPS backup systems are of this same modified sine wave type.  By in large most electronic equipment such as radios TV’s, stereos and computers will work satisfactorily given the less than perfect sine wave AC input.  With today’s technology, large power transformers and linear regulators have mostly given way to transformerless switching supplies which are less critical of the input waveform.  For the more critical applications, pure sine wave or “true sine wave” inverters are available typically at higher costs.
You might ask if the modified sine wave output generated by these power packs is a problem and are there certain types of equipment that should not be used with such inverters.  Xantrex [2], who makes the Duracell PowerPack, suggests avoiding equipment  using a zero-crossing detector sampling the AC power such as inexpensive clocks and timers which derive their timebase from the AC power.  Xantrex also suggests many models of electric blankets, laser printers and other devices that regulate heat using a microprocessor and may not operate correctly if connected to a modified sine wave inverter.

If you are interested in determining the quality of a given power source, you might consider the Fluke 345 [3] clamp on power quality meter which will display the waveform and identify harmonic components out to the 30th.  The Fluke meter is a professional quality instrument and a little pricey selling for something on the order of $2500.  Sears sells a product manufactured by Kaito Electronics, Inc., the Sinometer MS2208 [4]  Power Factor Clamp Meter.  The Sinometer has less functionality than the Fluke and does not display any waveforms, but will measure harmonic distortion which relates directly to sine wave purity.  The cost of the MS2208 Sinometer is on the order of $250.
Essentially all the Ham Radio gear offered today has been designed to operate from a 12 Volt DC source, thus, eliminating the need for an AC inverter.  However, some support gear and other critical household items may not be provisioned to operate on DC power.  For those appliances, the AC inverter power pack has great utility for emergency backup.

[1]  Duracell Powerpack 600:  http://www.duracellpower.com/backup-power/power-packs/powerpack-600.aspx
[2] Xantrex Tech Doctor; Sine Wave vs. Modified Sine Wave  technical:  http://www.xantrex.com/documents/Tech-Doctor/Universal/Tech1-Universal.pdf
[3] Fluke 345 Clamp Power Quality Meter: http://www.fluke.com/fluke/usen/power-quality-tools/troubleshooting-power-meters/fluke-345.htm?PID=56070
[4] Sinometer MS2208: http://www.sinometer.com/pdf/MS2208.pdf