Friday, January 19, 2018

PM Yearbook Projects Part 2

So here are a couple more projects and an article from the PM 75-82 yearbooks. So I will start off with a clear but too short article on Ohm's law.

The 1 HP = 746 watts statement can be deceptive and would have benefited from further explanation. This only applies to a 100% efficient system. A heating element is 100% efficient. Most other electrical equipment is not. Motors are generally 65% to 75% efficient at the shaft output. Some claim efficiencies as high as 82 or 83%.

As a general rule I look for a 10 Amp draw at 115 Volts per HP give or take a bit. This gives you 1150 watts, which equals 65% efficiency. Also be aware that starting loads can be two or three times higher. Modern breakers usually have built in time delays to compensate for this. Imports will often only include voltage and HP on their labels. Their's a very good chance they are using Ohm's law to determine HP disregarding the actual efficiency of the motor. The only motor which can approach 100% efficiency would be one constructed from superconductive materials, and superconductivity at room temperature is still many years if not decades away.

If you have a small lathe and basic welding equipment the next project is very useful around the shop. You can make quick and easy scroll work, hooks, brackets, and decorative metal work with this solid metal bender.

The next project is also very useful in the shop and around the house for producing accurate square cuts in  many different materials from glass to photo mats, and this cutting board conveniently folds up for storage.

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