Dynamote's "Brutus" a 2.3kW. Sine Wave Inverter tested by Richard Perez Brutus makes 2,400 watts of pure sine wave power. This large inverter's 120 vac output remains stable under brutally inductive loads like 3/4 horsepower electric motors. At 96› a watt, Brutus is affordable by those whose work requires ultrastable sine wave electricity. Shipping Container and Documentation Brutus arrived in fine shape. The shipping box is rugged enough to support Brutus's 65 pound bulk (8 inches high, by 15 inches wide by 15 inches deep). The documentation is straight- forward and gives enough data for proper installation and operation of Brutus. Dynamote builds Brutus for use in vehicles. The manual reflects Brutus's mobile heritage and could use wiring diagrams for photovoltaic, wind, and microhydro systems. The manual contains sections on batteries, power cables, and even a list of required tools. We had no trouble installing the inverter. Brutus's Specifications Brutus converts 12 Volt DC power into 120 vac, 60 Hz., sine wave power. Dynamote specifies output at 20 amperes at 120 vac. Output surge amperage is rated at 90 amperes at 120 vac. Brutus is rated for 2400 watts continuous operation and 10, 800 watts under surge. This is a large inverter. Dynamote rates power purity at less than 3% total harmonic distortion (THD), and places NO limitations on the power factor of loads. In nontechie terms, this means that the output power is a constant peak, pure sine waveÄthe same as utility power. No limitation on power factor means that Brutus will power big inductive loads like electric motors and still maintain this pure sine wave output. This is a feat that utilities have yet to accomplish. With specs like these, we couldn't wait to test Brutus. The Test System We installed Brutus in Home Power's inverter room. Brutus is connected via 6 feet of 0000 gauge cable to a fused disconnect and then to the power center. We used a 500 Ampere, 50 mV. shunt for measuring current into the inverter. The battery is composed of 150 pocket-plate nicad cells yielding a capacity of 1,500 Ampere-hours at 12 VDC (18 kiloWatt-hours of storage). We connected Brutus to our home/office's power distribution grid. This gave the inverter access to all the appliances in the home and office. We used three Fluke 87 DMMs and one Beckman 2020 DMM for true rms voltage and current measurements. We installed an oscilloscope watching the inverter's power output. We then proceeded to operate our household and business using Brutus power. Brutus's Performance The first stage of our testing was 3 months of just plain ole' user type testing. We immediately noticed that all our problem appliances stopped buzzing. We had become so used to hearing the buzz in the computers, the printers, the microwave, the swamp cooler, that their silence was deafening. We noticed other distinct performance improvements in our large appliances. Our swamp cooler uses a 1/3 horsepower, shaded pole, electric motor to turn the fan. This motor barely ran on slow speed when plugged into any mod sine wave inverter. On Brutus's sine wave power, we can use the slow speed on this blower and it spins just like downtown. The 800 watt microwave oven cooks about 30% faster. All the computer equipment (and there lots of it) runs silently and much cooler. Performance on our video and audio systems is flawless. There is no sign of 60 cycle hash and trash on sound, and no dark lines marring the video displays. Brutus also worked speed- controlled tools, like a Milwaukee 1/2 hp. drill flawlessly. This inverter is large enough to run a rock band, and clean enough to run any laser printer! Brutus is powerful enough and stable enough that we can do things we never dared to do before. Activities such as operating all the computers and the microwave oven and a power saw on the same inverter at the same time. We really had to work to get Brutus to shut itself off from overloading, which it did at about 3,000 watts output. Brutus protected itself against output over current, overtemperature, and low battery voltage. All these fault modes are manually reset by turning Brutus off then on again. We have operated Brutus at 16.3 VDC input, which makes this inverter compatible with alkaline battery systems. Brutus is very radio quiet. It is the only large inverter we have ever used that is not audible on our VHF FM radiotelephone. Karen spends half her life on the phone and loves Brutus for its silence alone. It is also quiet on AM radio, FM stereo, 2m Ham FM, and broadcast VHF TV bands. Brutus is a large sine wave inverter. It extracts a price for its power and purity. The price is efficiency. Brutus does have an effective sleep circuit that reduces its no load power consumption to 0.7 Watts. But once up and running, Brutus requires about eight Amperes at 12 VDC (96 Watts). This means that when we use Brutus, we should have a real job for it to do. After user testing, we took data on Brutus's performance. Here is a sample of our measurements of Brutus as it operated in our system. INSERT TABLE AND TWO CHARTS The table shows a variety of primarily resistive loads being powered by Brutus. From our data, Brutus meets Dynamote's specification for ñ5% rms voltage regulation. Frequency was a rock solid 60.00 Hz. on our Fluke 87. Even under full rated load, the waveform's peak voltage never fell below 160 volts. We also plugged a variety of large and nasty inductive loads into Brutus. We tried motors, transformers, and the switching power supplies used in computers. We watched the oscilloscope in fascination as the inverter never deviated from a smooth and regular sine wave. This inverter didn't care what we plugged into it! Efficiency below 300 watts is low, but between 300 watts and 2000 watts power output efficiency is well above 80% by our measurements. This is about 12% less efficient than modified sine wave inverters because Brutus makes sine wave power. Our actual measured peak efficiency is higher than the 83% claimed by Dynamote for Brutus. The rms voltage, peak voltage, and frequency data we collected from Brutus far exceeded our expectations. We checked the instruments and did the tests again. We could still not measure any deviation from the pure sine wave. We doubted our instruments until... Brutus meets the BMI Powerscope at SEER '92 George Patterson, an electron wizard and long-time home power fellow, showed up at SEER with a BMI Powerscope. This 25 kiloBuck instrument has only one mission in life: measuring electric power. Consider it a computerized connoisseur of commercial power (see sidebar). George hooked the BMI Powerscope to Dynamote's Brutus and started taking data. We at Home Power Central work very hard to collect accurate data with affordable instruments. Never in our wildest dreams have we ever been able to sick an instrument like the Powerscope on an inverter. The Powerscope verified Dynamote's claim of less than 3% total harmonic distortion (THD). The Powerscope measured less than 1% THD on most data runs, with a high of 2% THD when Brutus was running a 3/4 horsepower electric motor on an almost discharged pair of car batteries. The Powerscope also agreed with our measurements regarding rms stability, peak voltage stability, and frequency stability. George commented that Brutus delivers power which is more stable and better regulated than the grid... Putting Brutus to work Brutus is best for serious work in large systems. If you load this inverter to 400 watts or more, then the efficiency loss for using sine wave power is small. If you use Brutus to power a couple of 11 watt compact fluorescents, then the efficiency penalty is severe. Brutus consumes 90 Watts once operating, so you'd best have work for it to do. Use Brutus for large jobs that require clean, sine wave power. For example, the combined wattage of all our computers is about 500 watts. These computer operate just about all day every day. In the morning, we plug our home/office into Brutus for clean, silent power all day. After work is done, we plug ourselves into a mod sine wave inverter to run lighting and small appliances more efficiently all night. Brutus would be at home powering communications businesses, recording studios, video editors, computer based businesses, wood shops, and metal shops. Brutus will power loads like laser printers, laser based copy machines, and triac controlled appliances that will not function on modified sine wave power. A modified sine wave inverter costs about 70› per continuous output watt. The Brutus inverter costs 96› per continuous output watt. List price of a Brutus 2400 is $2295 with a one year warranty. Making a pure and stable sine wave at this high output power level involves electronic design compromises that lower the inverter's efficiency. We, at HP Central, have been using about 3,800 watt-hours of power out of Brutus each day. The efficiency penalty paid is 12%, or 580 watt-hours per day in our case. This is the amount of power produced by 2.5 standard 50 Watt PV modules. For us, the additional cost and power consumption is far outweighed by increased performance. Conclusions Brutus is a large, super stable, pure sine wave inverter that really works. Dynamote gets thumbs up for making downtown power possible and affordable for home power systems. The quality of Brutus's power is superb, better than the grid can deliver. Access Author: Richard Perez, c/o Home Power, POB 275, Ashland, OR 97520 ù 916-475-3179. Test assistance by Chris Greacen and George Patterson. Maker: Dynamote Corporation, 1200 West Nickerson, Seattle, WA 98119 ù 800-426-2838 ù 206-282-1000