Dryer vs GFCI

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FionaZuppa said:
How do you mean? Higher voltage with less amps will always "use" less power if the output remains the same.
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Umm... disregarding for PF just for sake of conversation, assume a 120 volt motor @ 5 amps compared to the same motor running on 240 volt @ 2.5 amp. How many watts is each motor?
 
LarryFine said:
Actually, within a certain range, power out = power in.
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Which range would that be?

Besoeker3 said:
Not quite that it follows.
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Example please.

infinity said:
Are you talking about losses in the branch circuit wiring? Otherwise watts are watts.
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Think about it, why would where you look be questionable? If it has a wire and has amps, there's wasted power, period. BC, motor, etc, make no diff. Lower the amps you lower wasted power. The realm of superconducting and stuff like that is not applicable anywhere as of now.

texie said:
Umm... disregarding for PF just for sake of conversation, assume a 120 volt motor @ 5 amps compared to the same motor running on 240 volt @ 2.5 amp. How many watts is each motor?
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Your example would not have same output power. Use 240/2.5A as the reference point, you would need a bit more than 5A @120v to get the same output power.
 
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FionaZuppa said:
Which range would that be?
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The design voltage range of the motor. Motors tend to be constant-power loads. For a given mechanical load, a 208/240v motor uses more current at 208v than at 240v, but the Kva is roughly the same throughout that voltage range.

If it has a wire and has amps, there's wasted power, period. BC, motor, etc, make no diff. Lower the amps you lower wasted power.
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Ah! Current. Before, you said "power."

Your example would not have same output power. Use 240/2.5A as the reference point, you would need a bit more than 5A @120v to get the same output power.
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Not if you use a larger circuit on 120v to keep the voltage drop percentage equal.
 
LarryFine said:
Not if you use a larger circuit on 120v to keep the voltage drop percentage equal.
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Ah, was anticipating this one. Surely true, but has low probability of being practical in any way. The dryer recepts (for resi) are always what NEMA form factor? And, I was not so concerned about the BC wire, was only focused on the motor itself, more amps in the motor, more wasted heat (aka "power").

There will be no practical case (application of wiring) where the 120v BC uses wire any bigger than the wire used for the 240 recept.

If my gas dryer had option to make motor(unit) run from 240v, I would swap the cord and plug it into the 4wire 240v recept.
 
The motor will use the same power to produce the same power. The overall circuit "benefits" by the higher voltage.
 
Consider for a moment a 'dual voltage' motor, one which can be connected for 120V or 240V operation by changing the terminal block arrangement.

Internally the coil voltages and currents are exactly the same. You simply have a pair of 120V coil sets which are either in series or parallel. Externally you see the current difference....with one exception that I've encountered.

Sometimes in capacitor start single phase motors the starting coil set does not get reconfigured for different voltages even if the run coils do get reconfigured. This would presumably cause a real efficiency difference during starting.

Jon
 
mbrooke said:
That is unless you count voltage drop.
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I did, and have, but that's a function of the power source and supply circuit, not the load.

Theory covers just the motor, practice includes the entire circuit. Which are we discussing?
 
LarryFine said:
I did, and have, but that's a function of the power source and circuit, not the load.

Theory covers just the motor, practice includes the entire circuit. Which are we discussing?
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Theory covers everything- including how just starting the dryer pulls the frequency down of the entire eastern interconnection.
 
Years ago, I was attending a continuing education class for one of my licenses. The instructor was pushing 3/0 for a standard residential oven, claiming power savings due to less voltage drop would pay for the wire upsize in two years! LOL!
 
curt swartz said:
Gas dryers are 120 volt. Dryer manufactures want to use the same motor in both gas and electric models.

Even if they started using 240 volt motors in new electric dryers we would still be installing 14-30 receptacles to accommodate older dryers.
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No longer true. Most modern dryers now use a 200V 3 phase motor and a VFD (PC board mount) inside. Then they have what’s called a “voltage doubler” circuit for when it is used at 120V, like on a gas dryer, or it just takes in the 208 or 240V single phase and recreates 3 phase for the motor. In addition, the controls are all electronic now and use a Switch Mode Power Supply that can accept anything from 100-240V input without having to change anything. One motor, one control system, one design regardless of where in the world it goes. It’s been that way for about 10+ years now.

the problem now is that our new codes require a GFCI for the dryer and VFDs don’t play well with GFCIs. Some hold, some do not. One thing for sure though, your grounding has to be PERFECT. No cheating, no fudging.
 
Jraef said:
No longer true. Most modern dryers now use a 200V 3 phase motor and a VFD (PC board mount) inside. Then they have what’s called a “voltage doubler” circuit for when it is used at 120V, like on a gas dryer, or it just takes in the 208 or 240V single phase and recreates 3 phase for the motor. In addition, the controls are all electronic now and use a Switch Mode Power Supply that can accept anything from 100-240V input without having to change anything. One motor, one control system, one design regardless of where in the world it goes. It’s been that way for about 10+ years now.

the problem now is that our new codes require a GFCI for the dryer and VFDs don’t play well with GFCIs. Some hold, some do not. One thing for sure though, your grounding has to be PERFECT. No cheating, no fudging.
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Low end dryers are still centrifugal induction.
 
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