Guess how many Amps ths 220 VAC HVAC motor draws at 110 VAC?

"If it was a straight resistance" That would be a DC motor.

This AC motor has impedence.

Without taking out some equipment and measuring the power factor my guess says about 4.5 amps

In theory it SHOULD be 3.8A

and the motor should be generating 4x as much waste heat as it was before

snipped-for-privacy@aar> Guess how many Amps this 220 VAC HVAC motor draws at 110 VAC?

Roy,

I believe that you are correct about phase angle.

Are you saying that an analog meter at 60 HZ could be grossly inaccurate?

Would you guess the current at 110 VAC be 1.9 Amps drawn at 220 VAC and measured on a Simpson meter?

Maybe you should ask "who cares?" first.

Oops! You mean it would 1/4 the POWER (watts) at half the voltage. At 1/2 the voltage, a straight resistance would actually have 1/2 the current (Amps), not 1/4. I (amps) = E (volts) / R (ohms)

Of course, the above is only true for a straight resistance. Motors are very different. Motors, even DC motors, are active (not passive) devices and their behavior depends on many factors and often seems to defy simple explanation.

Vaughn

I agree.

Look at it this way: 220 VAC motor;

Let's assume that the rotor-locked resistance is 20 ohms simple resistance.

If we apply 220 VAC and prevent the motor from turning, it will draw

Follow me so far?

O.K. We release the motor and it turns 1075 which is the design rpm.

No longer is the resistance simple, the rotational speed, and the current, causes a back EMF which adds a dynamic resistance called impedence to the mix.

No longer is the current 11 Amps, it is now ~ 2 Amps.

The motor is acting like a 110 Ohm load and only 2 amps will flow.

We now reduce the applied voltage to 110 VAC. Assuming the same 20 Ohms of simple resistance with the motor stopped, it will now draw 110/20 or 5.5 Amps (half that at 220)

O.K. we release the motor and it spins up but not to a full 1075 rpm.

Why? Not enough voltage to push enough current to create as strong a magnetic field as

The back EMF will also be weaker.

I measured the current yesterday with 110 VAC applied as being slightly less than 1.9 Amps!

Wonderful, isn't it?

No.

The spec on the motor reads 208-230 VAC 1.9 Amp.

It came right out of a condenser.

It is running slow and sure at 110 VAC.

By next week, when I receive my mercury contactor, it will be at 220 VAC, controlled by a 110 VAC line thermostat.

That's a lot like asking "do I have more or less stuff in my pockets." i.e. a fairly meaningless question without more information.

At full rated load (which is where the rating amps is a relevant #) I would expect that you draw somewhere between 6/2 and 12/2 rated full load current. But since the motor is turning, we can be quite sure that you are not at that point. jk