Three Letters Re: Small Scale Alternative Energy in Suburbia

Mr. Rawles:
In a recent SurvivalBlog post, Alan W. wrote:

“It has a 400w inverter with a modified sine wave output. During Hurricane Irene the
only thing that I could get it to power was a standard lamp with an incandescent light bulb! It wouldn’t run tools or electronics.”

I believe he is drawing the wrong conclusion from this experience. Instead of blaming the (admittedly inferior) “modified sine wave” inverter, he should have blamed himself for not testing his equipment before the emergency struck.

I own a number of inexpensive inverters with “modified sine wave” ranging from 175 watt to 1000 watt ratings, and have found they run almost everything I have tried to power with them. I have run lights, both incandescent, CFL, and long tube fluorescents with both old magnetic and modern electronic ballasts. I have run sound reinforcement equipment
including mixers and power amplifiers (with a slight buzz but no damage).

Every night I run my CPAP [sleep apnea breathing] machine and charge my cell phone using an inexpensive 200 watt rated “modified sine wave” inverter running from a deep cycle battery that is charged by a small solar electric system.

One way to be almost absolutely sure that an electronic device will be happy running from a “modified sine wave” inverter is to look at the acceptable power voltage range. Many electronic devices today have “universal” power supplies that will accept any voltage from 100 to 250 volts. Such universal power supplies have zero problems using the less than great output waveform of inexpensive inverters. Both my CPAP and my cell phone charger have such universal power supplies.

As far as the tool issue, most motors require 7 to 10 times their running power to start. It is possible that the 400 watt inverter was simply not big enough to run the device he tried to use.

It is also very possible that he had a defective inverter.

He also stated:

“An inverter with a pure sine wave output is a much more expensive design
(and is the same output as your house electric) and is typically larger. It
is often used in back-up power supplies for computer systems.”

Most reasonably priced computer UPSes sold in the home and small business market, have “modified sine wave” outputs, not “pure sine wave”. Our computers at home are running on four different APC brand UPSes, all of which have “modified sine wave” outputs. This is another example to disprove the common myth that electronics can’t run on “modified sine wave” inverters.

And, regarding:

“I realize that the typical generator uses a cheaper inverter and that may
be fine for a few lamps and a refrigerator, but I want to run medical
equipment, Televisions and a laptop during outages.”

The “typical” generator does not use an inverter. The modern inverter generators popularized by Honda with their very quiet EU series of generators do use inverters, and the Honda models have a pretty good “pure sine wave” output.

There may be medical equipment that has a problem running on “modified sine wave” inverters, but I suspect many dealers and manufacturers claim pure sine wave is required for liability reasons rather than any actual technical reason. Again my CPAP is perfectly happy running on “modified sine wave” power.

Laptops mostly have universal power supplies these days which don’t much care how good the power is you feed to them. In the case of a laptop a better solution is to use a power supply that runs directly from the 12 volt DC battery. This is much less wasteful of energy.

Televisions and radios may pick up noise when running on any inverter because even the best “pure sine wave” inverter has RF trash on its output. Try this before hand and see how much of a problem it is in your situation.

JWR wrote in reply:

“Even the best inverters produce AC power with a slightly clipped or distorted waveform.”

This is true. You can largely clean the power up by using a Harmonic Neutralized Constant Voltage Transformer such as the models made by Sola. I have both a small 50 watt and a large 1,000 watt Harmonic Neutralized Sola and use them to provide clean power to very finicky “power prima donna” electronics. The downside of these transformers are that they are large, heavy (my 1000 watt transformer weighs 80 pounds), waste some of the power, and are expensive even if bought used.

JWR Also mentioned:

“Also, when sizing your system remember that the larger the inverter, the
higher its “idle” current draw will be.”

That is a very important point. That is why I use a small 200 watt inverter to power my CPAP machine and my cell phone charger. Nothing larger is required. Regards, – R.R.


As a former truck driver, I have used inverters to power all sorts of things in the truck for about 10 years.

I have run various power tools, laptops, desktop computer, and even a deep fryer,cooker combo on my inverter.

The little cigarette lighter plug style inverter puts out around 50-70 watts. It would not power my laptop, but it would charge the battery, it works great for the little household adapters. They usually run around 30-40 dollars at a chain truck stop.

I used a Cobra 800 watt inverter that powered a desktop computer and CRT monitor. This was back in 2000 when laptops were still very expensive compared to desktops. It was mounted in the truck where the television normally goes. I could go many hours on the four batteries in the truck while still being able to start the engine later.

I later upgraded to a 1000 watt inverter to power my cooker, after having problems with my truck mounted diesel genset. With the high maintenance costs of running that little diesel generator, I would have been better off buying 6 or 8 additional deep cycle batteries and installing a second alternator. I spent nearly as much on the little generator as I did on the care of the 500hp Detroit diesel that got me down the road. – M.B.


Instead of spending a lot of money to get a pure sine wave generator or inverter, I’d like to remind SurvivalBlog readers of something that has been mentioned here before: You can place a UPS power backer in the line between the generator/inverter and your electronics. Let the generator charge the UPS battery with squarish sine waves and run the electronics off of the inverted battery power by the backer which is made to run sensitive electronics. I started using UPS seriously when our local power company (famous for high voltage spikes) kept burning out high quality spike protectors. The UPS power backers, take spikes, browns and square waves all the time providing clean power to your electronics. A power drop won’t even drop the satellite TV connection. The down side is that you have to replace the battery every few years or so. I’ve had the internal batteries last for as long as 5 and as few as 2. Almost every electronic device I own is on one except for large current drain items like laser printers and appliances. Those items stay on surge protectors which I do replace as they fail. – F.B. (15 Miles From Asphalt)