fiftyohm

david tigwell, Houston, TX, US
member


Birthday: 09/01/1955



Recent comments


Re: STL 49: Power Tool Power

Hey Ed- I wouldn't call it 'blather' at all. You apparently just misspoke. Either way, the podcast is a staple of my Saturday mornings. I enjoy it immensely, laugh, cry, hurl, and always learn something. Keep it up, Buddy!

BTW: I caught Mike's video on ammonia fuming with 'regular' ammonia. Guess that answered the question we discussed last year. Talk to you soon.

Re: STL 49: Power Tool Power

Hey gentlemen. Don't let our pal Ed do any wiring for you. 230 volt equipment does indeed require two circuit breakers on each 115V leg - but there is no "neutral"! The third wore is the Ground! Current does not, (or should not under normal operations), flow in that wire. It flows only between the 115V legs. The voltage in these is out of phase by 180 degrees, so the voltage across them is 2 X 115 or 230V. As the current flowing out of one leg must return through the other, the breakers see identical current. Therefore, if you have a pair of 20 amp breakers on your 230V circuit, you have a 20A circuit - not 40 amps.

Also, with motor ratings, efficiency is a huge issue as alluded to in the podcast. Universal motors, (really AC/DC motors), have efficiencies at load on the order of 60%, or even less. This means that when loaded, they not only slow down, but they get HOT. Table saws, Matt's big jointer, and other stationary equipment use induction motors. These run at constant speed, regardless of load, and are much more efficient - on the order of 85-90%. Very large, 3-phase motors achieve better than 95%. All this means they run far cooler at a given mechanical output than universal types.

All this is why we use induction motors for table saws. If you substituted your 3 HP router motor in your table saw and tried to rip 8/4 oak stock with it, you would shortly see smoke coming from the stock as the blade slowed down, and shortly thereafter from the motor. After that, it would billow from the base of the saw cabinet as the molten metal from the motor fell into the dust collection area.

Re: Video Sneak-Peek of New Groundbreaking Video Workshop Series

I loved the cabinet maker's triangle done with the Sharpie. Classic!



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