EXELTECH's SI-250 Sine Wave Inverter Tested by Richard and Karen Perez The big news is completely clean, glitch-free, audio, and video from inverter power. This inverter makes SINE WAVE power. In our test we powered a variety of stereos, radios, TVs, VCRs, and even a satellite TV system. All delivered noise free performance. Gone was the annoying audio buzz on the stereo, gone were the tiny black lines on the TV screen, all gone! It makes Sine Waves! The Exeltech SI-250 inverter takes battery stored 12 VDC and turns into 120 vac sine wave power. The SI-250 is rated at 250 watts rms continuous output (2.12 amperes rms). This inverter makes true, smooth, sine wave power, not the modified sine wave power produced by almost every other inverter. Modified sine wave inverters work well, are ultra efficient and reliable. But they ALL have one major problem. When delicate electronics like VCRs, TVs, radios,and stereo are fed modified sine wave power they have glitches. The sound portion of the program has a loud and obnoxious buzzzz that underlies everything. On the video screen, whether fed by a VCR, broadcast TV, or satellite TV, there are thin horizontal noise lines marring the picture. We've gotten used to the fact that modified sine wave inverters don't power entertainment electronics very well. We've learned to live with the noise and glitches. Well now we don't have to take it more! The SI-250 This is a small inverter designed for use with a 12 Volt battery. It measures 3.5 inches high by 4.5 inches deep by 9 inches wide and weighs 3.5 pounds. The supplied documentation is adequate and contains a full set of technical product specifications. The voltage operating range of this inverter is 10.5 to 16.5 VDC, making it nicad, nickel-iron, and lead acid compatible. We operated it at 16.8 VDC with no problems. The surge rating of the inverter is 350 watts for three minutes, but we got 380 watts out for 7 minutes and 7 seconds (room temp 78¡F.). The SI-250 is equipped with over voltage protection at 17.5 VDC, and under voltage protection at 10.5 VDC. It is fully protected against any output overload or short circuit. The Test System We wired the Exeltech SI-250 into a 600 Ampere-hour, 12 Volt nicad battery system. This system is sourced by a PV array of sixteen modules. During our test we set the voltage regulator to maintain a voltage of 15.15 VDC. Testing the SI-250 We used Fluke 87, true rms reading, digital multimeters to make the measurements. We inserted a 100 Ampere, 100 milliVolt shunt in series with the inverter's negative power line to the battery for DC current measurement. We also hooked up a Tandar oscilloscope so we could watch the inverter's output waveform. We used 120 vac incandescent light bulbs as loads for the generation of the data shown on the table. The very first thing we noticed was the inverter's waveform on the oscilloscope. It was a perfect, smooth, sine wave. To see this sine wave, produced by an inverter, was a thrill for all of us. We then proceeded to put the inverter through its paces, and produced the data in the table below. Insert Table The Exeltech SI-250's Performance This inverter exceed every specification of its maker. A quick look at the data will show that its voltage output (both peak and rms) was extremely stable. We have never tested an inverter with this degree of stability. We stared, fascinated by the inverter's waveform on the scope. Even during overload, the inverter's waveform stayed as smooth as a baby's behind. We also ran a variety of inductive loads, like a VCR, a 21" TV, and a satellite TV system. The inverter's waveform never varied from a perfect sine wave. In actual fact, this inverter puts out power that is far more pure and stable than any available from a commercial utility. We measured the inverter's no load current consumption at 0.74 Amperes. No load power consumption was 11.2 Watts DC. We were able to operate 280 watts of lightbulbs for twenty minutes without shutdown. We repeatedly overloaded the inverter with a 1,000 watt electric heater and the Exeltech protected itself against damage. We measured the inverter's peak output at 6.89 amperes rms with a Fluke 87 in 1 millisecond record mode. The efficiency of this inverter is less than the modified sine wave types. It's a case of we don't get something for nothing. Our data shows efficiency in the range of 65.7% for a 23 watt load, to 81.9% for a 132 watt load, and an efficiency of 81.3% for 281 watts output. This is about 15% less efficient than modified sine wave inverters. Performance on our delicate electronics was and is outstanding. In our opinion, the increase in pleasure produced by buzz-free music and glitch-free video far outweighed the SI-250's lower efficiency. When we watch a movie on the VCR and big 21 inch Sony TV, we use an additional 75 Watt-hours of power from our system by using the SI-250 inverter instead of a modified sine wave inverter. This is about the daily production of one-third of one of our PV modules. We think the increased power consumption is worth the noise-free performance. Applying the SI-250 This is not a whole-house inverter. It only puts out 250 watts. It has no sleep mode, and high no-load power consumption. This inverter is suited for one thing Ð powering noise sensitive electronics. It is best suited as a second inverter for those of us who already own large modified sine wave inverters. We use our SI-250 exclusively on our audio, radio, TV and video equipment. Here it gives us better music and better video than we have ever had from our PV/Wind system. Conclusions The era of sine wave inverter is here. The Exeltech SI-250 is the cleanest and most stable inverter we have ever tested. At a cost of $325, it is well worth having just as a second inverter to power just the audio and video gear. We use ours daily and sometimes plug our entertainment electronics back into one or other of the four modified sine wave inverters we use. We hear and see the noise and glitches that ruined our entertainment for years and immediately plug our fun back into the Exeltech! Access Authors: Richard & Karen Perez, c/o Home Power, POB 130, Hornbrook, CA ¥ 916-475-3179 Maker: Exeltech, Inc., 7018 Baker Blvd., Fort Worth, TX 76118 ¥ 817-595- 4969