Sir:
I had purchased two Schumacher brand Portable Power packs-essentially a [gel cell] battery with [just] an inverter without the extra buzzers and bells from a company that makes quality battery chargers. 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. After some Internet research, I found that most units used the modified sine wave because it is a less expensive design. Unfortunately, it may or may not supply power to the unit that you need to turn on and it could damage some electronics.
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. These are not portable. Even the the top end Xantrex unit uses an inverter with a modified sine wave output. If anyone has any advice on where to find a portable unit with an inverter with a pure sine wave output. 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. Any ideas? – Alan W.
JWR Replies: From what I’ve read, the term “pure sine wave” inverter is a bit of a marketing myth. Even the best inverters produce AC power with a slightly clipped or distorted waveform. (And for that matter, even utility grid power doesn’t have a perfectly symmetrical waveform.) But both Xantrex (formerly Trace) and Outback manufacture sine wave inverters that produce very “clean” power that works very well with even the most finicky electronics such as desktop (AC transformer) computers and laser printers. Some of their small, low-wattage models are ideal for small photovoltaic, wind, or microhydro power systems. To save money, look for sine wave inverters in used condition, via eBay or Craigslist. But be sure that they are guaranteed to be working. (Commonly called a “No DOA” Warranty.) Also, when sizing your system remember that the larger the inverter, the higher its “idle” current draw will be. Even without a load, they put a load on a battery bank. Again, the higher the wattage rating, the bigger the idle current draw.