Woodworker's Journal 2006-30-2, страница 13
2 HP? Based on the selection of letters below, it's clear that even the experts disagree on the right answer to the question: 'Can you develop 2 MP on a 110-volt machine in the real world?" USA motor manufacturers' web sites. Grizzly has our own motor dynamometer capable of accurately testing motor HP-Further; a test lab in Taiwan independently tests our motors. Then we compare our test results to verify what we claim is indeed fact. Further still, had you looked at the motor label it clearly states our 2 HP motor will use 12 amps at 220V and 24 amps at 110V. Bill Crofutt Quality Control Manger Grizzly Industrial Inc. I recently read your review of contractor's saws. You mention in the article that you are suspicious of claims by the manufacturers that they have 2 HP motors. 1 am not a motor engineer, but I am an electrical engineer at Motorola, so I did some research. Motors in the l'i to 2 HP range can nowadays achieve efficiencies of up to 90% (see NEMA standards). Let's say we draw 15 amps from a 120-volt outlet (most are fused at 20 amps). The power delivered to the motor is then 15 times 120 or 1.800 watts: this is called Watt's Law. 1 HP equals 746 watts, so 2 HP would require 1,492 watts delivered to the blade. The efficiency of the motor would have to be 1.492 + 1,800 or 82.8%, which is achievable. So it is possible, with the right motor, to deliver 2 HP to a 120V operated table saw blade. Dave VanStone Arlington Heights. Illinois 1 shared Mr. Crofutt's letter with an electrician friend for another opinion. — Rob Johnstone Dear Rob, Mr. Crofutt is right. According to the NEC (National Electrical Codes) code book, you must have 24 amps to produce 2 HP on a motor at 110V. Furthermore, Part II of Article 430 requires that the conductors supplying a single motor used in a continuous duty application be sized at not less than 125 percent of the motor's full-load current rating, based on Tables 430.147 through 430.150. (Multiplying 24 by 125% means that a 30-amp circuit is required.) I have to say, that homes with a 30-amp, singie-pole circuit are rare as hen's teeth in my experience. Most people would need to get a special circuit with sufficiently sized (#10 minimum) wiring and a 30-amp breaker installed to meet these requirements. Mark Banks Jefferson Electric Company Beamount. Texas Final Thoughts And so 1 stand corrected. It is technically possible to get 2 HP from a 110-volt circuit. The larger point that I was making in the article, that a contractor's saw is not the saw to choose if you are after significant power, is still correct. I was able to stall out every saw in the test while cutting dimension lumber... including the Grizzly ... with ease. And by the way, the engineer 1 originally interviewed for the story, who happens to work for one of the companies in the test, stands by his statement that these motors do not, in the real world, develop 2 HP. (Circle No t on PRODUCT INFORMATION form) (Circle No 90 on PRODUCT INFORMATION form) Turning Point Studios presents yeung Chan in a hands-on workshop MAKING HAND TOOLS May 10-14, 2006 Make three elegant hand tools designed by Yeung Chan. Top photo by Aid Chnstnu CHRISTIAN BECKSVOORT in a hands-on workshop Build a wall cabinet April 17-21, 2006 678-438-0468 Woodworker's Journal April 2006 13 |
