MOTOR VOLTAGE

120V or 240V?

The question  "Will my saw motor run better or use less electricity if I switch it to 240V ?" is often asked and almost as often, an incomplete answer is given.
 

Let's stick with the facts.
First, a motor that can be wired to run using either 120V or 240V will draw half as many amps on 240V as it would on 120V. For example, a motor that draws 14A@120V would use 7A@240V. Likewise an motor that uses 12A on 240V would draw 24A on 120V, which is one of the reasons you don't see many higher HP motors run on 120V.
Second, a motor will typically draw anywhere between 2 to 6 times the rated amps at startup.

Will a motor run better on 240V than it does on 120V? The answer to that depends. If the 120V circuit is capable of providing the necessary amps, you will see no difference when you switch to 240V. But, if there are any inadequacies in the 120V circuit and it isn't able to provide the needed amps, you will see an improvement on 240V and it will be most noticable at startup since that's when the motor will place the highest demands on the circuit. For example, if you have a motor on a 120V-20A circuit, it might require more amps than circuit can provide when it starts up. On a 120V-15A circuit it almost certainly will need more than the circuit can provide. So you'll either get a tripped circuit breaker, or more likely, you'll just starve the motor of the increased amps at startup. You'll hear two sounds as the motor starts up. The first will be a sound of the motor coming up to speed and a second or two later you'll hear a difference sound of the motor running at full speed. Switch that motor to a 240V-20A circuit and now the motor draws halfs the amps. At startup it will be able to get the increased required amps from the circuit. And what you'll see is the motor that took a second or two to come up to full speed when it was on 120V, now SNAPS to full speed in a fraction of a second. It's not that the motor is any more efficient at 240V that it was at 120V, only that the shortcomings of the 120V electrical supply are no longer an issue. The first thing to do before you convert your 120V to 240V is to run the motor on a dedicated 120V circuit. Find a circuit that doesn't have anything else one it, not even lights. If you have a 20A circuit that's even better. That might be all you need to see an improvement in performance.

So will a motor use less electricty on 240V? The answer to that is no. The amount of electricty used is the voltage multiplied by the amperage. 14A muliplied by 120V is equal to 7A multiplied by 240V.

Click here for motor wiring information or how to have multiple 120V and 240V run off one circuit with a 120V/240V power strip. .

If you don't believe me then check out the woodbutcher.net website... and you'll see that he agrees with me. Which is a good thing... I think.

IN A PERFECT WORLD

In a perfect world, there is absolutely no performance difference in a motor running at 240V or 120V.

In a perfect world, our 120V circuits would be able to supply the amps required for the motor, which can be several times more than the rated amps on the motor plate at start-up. If the 12A motor required 36A (conservative) at startup the 120V circuit would not be able to supply it.

What typically happens is that a 120V circuit can't supply the necessary amps, especially at startup. So the motor experiences the symptoms of an inadequate circuit..... slower startup, etc.

When we switch that motor from 120V to 240V, we often move it from a 120V-15A or 20A circuit to a 240V-20A or 30A circuit, most often with the same or heavier gauge cable. That same motor that was sucking the 120V circuit dry at startup, is now only demanding half the amps. The 240V circuit can handle supplying the amps demanded by the 240V easily, but the 120V circuit couldn't.

So we see an notable "performance" improvement in a motor when we switch it to 240V. It snaps to life faster when it starts, compared to it delay it seemed to have when it was gasping for amps on the 120V circuit. What we are seeing is a motor that is no longer choking on an inadeqaute 120V circuit.

In a perfect world we would have 120V-60A circuits and a 240V-30A circuits and then we would see no difference at all between 120V or 240V. But how many of us are using a 120V-60A circuit before we switch to a 240V-30A circuit?

© 2008 Mark Goodall