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+-- Thread: New to woodworking - table saw advice (/showthread.php?tid=7336136)
RE: New to woodworking - table saw advice - TDKPE - 01-20-2018
(01-19-2018, 10:56 AM)Cooler Wrote: I had a dedicated outlet installed for the saw and my electrician suggested that it be 220 volt. I agreed and he changed the motor wiring for 220 volts. I don't know if that improves the performance or not. My electrician said it should and it did not add any cost to the job so I went with it.
It's more like running it at the higher of the two voltage essentially removes any chance of the wiring causing a reduction in performance. Like running with the choke out, the engine itself hasn't changed, but the air flow restriction causes a reduction in performance. Voltage drop on the wiring disproportionately weakens the motor at the lower voltage (compared to the higher voltage) because the current for a given load is twice as high, and the source voltage is half as much, and the torque curve drops as the square of the actual to nameplate voltage.
Heavy circuit wiring that's reasonably short is usually all you need for 120V operation, but configured for 240V, the wire gauge and run length are much less of a concern. Remember that with a CS with small motor, you're likely to push it well beyond its 1.5 hp rating, which means it could be drawing 20 or 25A (with a 15A or so nameplate rating), and loading it to 2 hp or higher.
Folks tend to push low powered machines until they're on the verge of or well into bogging (which is the feedback mechanism to the operator for regulating how hard to push it), and saggy supply voltage will cause a large increase in current* to drive the same load, and subsequent reduction in all points along the torque curve, making it feel a bit wimpy. The higher voltage reduces that effect markedly.
Startups are just the extreme case of bogging, where low voltage starting current can be 75-100A, and is where the phenomenon is most noticeable with quicker starting on the higher voltage with starting current being half that. With twice the supply voltage, the percent voltage drop is 1/4 that of low voltage on the same wiring, and with the torque curve sag being the square of the ratio, the torque curve sag from saggy voltage is negligible. Or zilch, as the motor is nameplated 115/230V, and the nominal supply voltage is 120/240, plus 5V, minus 10V. Or at least it's supposed to be. So odds are, even with a little voltage sag in the branch circuit, the voltage at the leads at 240V will be close to the design 230V (NEMA did that intentionally).
If it cost you no more money, then it was a win-win for you. Like opening the choke, and taking out the dirty air filter, and letting it breeeeathe.
*This, plus the saggy torque curve, is the basis of the "runs stronger and cooler" argument for running a CS motor on 240V. It's not always, or even frequently, necessary if the wiring is short and stout and you don't push it until it's grunting, but it's technically true, and can be very relevant (disastrous even) for long wiring runs especially, and working it harder than you probably should doesn't help. Just try starting a 120V air compressor on a circuit next to the panel, then on 100 ft of extension cord to see the difference. It may not even start with a long cord - my pancake wouldn't when I built my shed (I knew better, but tried anyway), so I ran it off a generator. Better still would have been a long hose with no generator noise, since air nailers work on a short impulse and don't care about long hose runs.