Wattage

[Matheous-2]

If an electric AC motor consumes 600watts of power at 240volts- would the same motor consume a similar wattage at 110volts?
I do hope the question makes sense!

[bert_h]

Not unless it's got an automatic voltage adapter, and I've never heard of them on anything bigger than an electric toothbrush recharging stand. Naively, it will take half the current at half the voltage, therefore a quarter of the power. But realistically, if there isn't enough power to turn it, it coul take a huge current and burn out, because some motors depend on their rotation to increase their resistance and limit the current they take.

[KARL]

If you use a step-up transformer (basically a step-down in reverse) to power the motor at 240V from a 110V supply, then the motor will use more or less the same wattage. There will be a slight loss in the transformer so the total consumption will be higher than directly from a 240V supply. The transformer needs to be rated a bit above the 600W to prevent it from overheating and risking its destruction.

[jake-the-peg]

The thing about electric motors is that as the coils rotate in the magnetic field they generate a back emf opposing the driving emf.

This automatically regulates the current so that if there's no load very little current will flow, as the load increases the current and hence the power used will increase.

I recall my father once discovered this trying to cut down a tree with a circular saw attached to a drill - as the tree gripped the blade the current increased until the drill went - bang!

So the load is more important in the power that is used in an electric motor.

If it's the same load then we're really talking about the efficiency of AC motors at different voltages

Now that gets complicated as they're designed for a particular voltage. If you run a 240 Volt electric motor at 110 volts it will be pretty inefficient similarly the other way around

[jake-the-peg]

Type Your Answer Here...So in summary to these answers - Yes I think we understand

But it doesn't quite work like that

Electric motors are tricky things

[mibn2cweus]

The only thing that can be stipulated regarding the variety of different types of AC motors is that they all run on AC . . . and even that is not always the case.

[EDDIE51]

In theory volts x amps = watts
So 600 Watts @240v is 2.5 amp
110 x 5.45 =600 so 5.45 amps @ 110v

[Matheous-2]

Sorry guys, I got this slightly wrong- it should be the other way round -a 600w motor running on 110v.
Is this similar to a 250w motor running on 240volts?
I am not talking of converting the same physical motor- I am asking if I should expect the same amount of power from the 250w/240v motor?

[EDDIE51]

Watts are the power so a 600 watt motor produces 600 watts of power, a 250 watt motor produces 250 watts of power. The lower the voltage the more amps needed to produce the same watts.
As I said Volts x Amps = Watts
,( I remember this equation from my 1st year physics back in 1962)

[jomifl]

yes

[Matheous-2]

Thanks guys- It's so long since I worked with DC motors- I forgot that rule.....

[beso]

EDDIE51//
In theory volts x amps = watts
So 600 Watts @240v is 2.5 amp
110 x 5.45 =600 so 5.45 amps @ 110v
//

Eddie uses the simple formula that applies only to resistive loads. The nature of AC electricity and its load is far far more complex. The magnetic filed in the device become dynamic.

Magnetic field build up and decay on each cycle. The properties of the magnetic circuit and the especially the air gap between the rotor and stator strongly influence the performance.

Moreover, the type of motor is vitally important. An induction motor would be likely to fail to reach pullout torque and never operate efficiently.

[Old_Geezer]

Apprecaite teh answer was covered, but as a general rule one could always assuem the resistence/reactance/impedance doesn't change too much. Therefore the fewer volts, the fewer watts. Were it not so you could connect it to a source of 0v and get free power.

now actually that's an idea... wait here a moment...

[Old_Geezer]

Appreciate the answer was covered, but as a general rule one could always assume the resistance/reactance/impedance doesn't change too much. Therefore the fewer volts, the fewer watts. Were it not so you could connect it to a source of 0v and get free power.

i]now actually that's an idea... wait here a moment... [i]

[Matheous-2]

OG - You had a eureka moment twice!!

[Old_Geezer]

Fate made the second one wrong also. I should have posted it as typed a third time for luck.