Motor Myths

So, with a high-efficiency motor, driving a squirrel cage blower, such as in a furnace, the filter condition would have greater effect than with a standard motor?

Score 1 for no answer......

And?

His bunk is bunk. Efficieny = work - losse. High efficiency motors reduce the losses. An increase in slip speed is all but meaningless, because it only matters when the motor is UNLOADED. So if a motor is UNLOADED during operation, it is doing NO work, ergo it has ZERO efficiency and arguing over the details become pointless.

Under load, the motor energy is commensurate with the work being performed, and "work" can be defined as an expression of energy over TIME to perform a task. If your task is to move liquid from A to B, and using the high efficiency motor makes the pump use 3.5% more energy to move MORE fluid over the same amount of time, or the SAME amount of fluid in LESS time, the energy is the same. But if you have decr4eased the LOSSES associated with making that motor work, then you HAVE saved energy.

Where is that article by the way?

Not exactly. We use shaded pole motors to run small pumps and automatic valves. Fractional hp and designed to operate at locked rotor for extended periods without overheating. The heat these motors generate when just running is significant when compared to the total power consumed.

These shaded pole motors are common in the industry because they are self starting and cheap to produce. I would be scared to consider the amount of fuel consumed just for these motors to heat their boxes...

Drew K

I'm not certain, but I'd be surprised if motors designed to operate at locked rotor for extended periods would be designed for high efficiency. Efficiency isn't high when stalled!

Exactly, but because overall consumption is low it is not considered a big deal. We build thousands of these every week. If I were tempted I would do the math on how much electricity our motors put out a week given estimated duty cycles. Across the globe these inefficient motors do become significant.

Here is the thought that comes to my mind, what do humans do with unlimited supply? They use without limit of course! As long as energy is cheap and abundant, efficiency will not be important. The world is screwed if we ever do develop cold fusion...

Drew K

Bringing Shaded Pole motors and their ability to stay alive with locked rotors into a discussion about induction motor efficiency is a red herring.

_{Note: the emphasis on the "c" added to efficiency above is to satisfy the resident spelling Nazi....
And give me a break, I typed that on an iPad, but this forum is horrible for iOS devices.}

By claiming you intended the word 'efficiency' originally you transform your mistake from inadvertent typo, to fundamental misconception of an important basic concept..

Efficiency is not 'work-losse'.

How so is it a red herring?

Drew K

The article in reference is about high efficiency AC induction motors. That would not be inclusive of SP motors, so it is not germane to the discussion to bring in how they can be held at locked rotor.

Perhaps, I took the topic to be motor power consumption vs work output. I am working with these low efficient motors right now and have only recently become aware of how bad they are. Many modern countries have been converting to led and cfl lighting for homes and offices in an effort to save energy. I would like to see a study on how much energy is consumed by cheap inefficient motors.

Drew K

Worthy goal, but not germane to THIS discussion. But since you asked, I think it is something that has been on topic for a number of agencies here in the US at least. A chief one I am familiar with is the Electric Power Research Institute (EPRI, a local (to me) think tank funded by the electric power and equipment industry, who's staffing consists of leading academics and scientists in the field. They do look at such things, might be work a glance through their archives to see what they have done so far.

http://www.epri.com/Pages/Default.aspx

Some of their work started as Government programs where they took over once the original program was de-funded. One such program was a series of studies done under the auspices of the Dept. of Energy, relating to studying the effects of energy efficient motors. They had a nice program in the 80's called "Motor Matters" that was the basis of many power utilities funding programs to replace older inefficient motors with new energy efficient designs. But what started to happen was that because of a lack of cohesion in establishing a common standard for what "energy efficient motor" meant, suppliers started throwing the term around like candy at a parade and watered it down. So EPRI did some studies to show the RANGE of inaccuracy that existed without that standard, which ultimately lead to positive changes in how people had to test and word their marketing claims. Much of that is available still through them, but it sometimes is difficult to wade through.

Another interesting factoid I stumbled across in the US Census bureau data: 60% of ALL electric power generated in the US is used for AC motors, and of that, 70% of all AC motors in use are on pumps of one sort or another. So given that Shaded Pole motors don't do well on pumps, the total effect of them on the big picture is going to be somewhat negligible.

Good info, thanks. I was hoping that it would be more significant. Consumers like green-scaping and since every bit does help I was hoping to start a revolution of energy efficient household fans...and save the world!

Drew K

Link attached. http://machinedesign.com/blog/5-common-motor-myth.

You appear to be agreeing with me, but not sure what you mean by "His bunk is bunk". Also increase in slip speed? Increase in slip means decrease in speed. Slip is negligible in unloaded condition (as I think you're saying)

'.... Efficieny = work - losse. ...'

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Okay. Never heard of 'efficieny' before. Learn something new every day. I am not sure how useful that metric is however.

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'Efficiency', on the other hand, being 'useful output/input', is very useful. Perhaps that is the reason the similar sounding 'efficieny' never caught on.

Are you sure the horizontal axis of your chart shouldn't read Percent of full load, not speed? At 100% speed there is no slip, no load and zero efficiency.

Most motors will stall if loaded to give 30% speed. But efficiency ~ 50% at 30% load looks about right.

I wonder why the 25hp and 50 hp models run counter to the otherwise consistent correlation of higher horsepower and higher efficiency.

It's not at all clear: Is this graph showing the efficiency of the variable-speed drive, of just the motor, or of the system of drive with motor?

If you want to save energy, there is more to save in the entire system rather than the motor, eg. alignment, bearing grease and conditions of the rest of the system.

Can a written pole motor be considered to have high efficiency?