Energy Saver?

[gar]

110415-2337 EDT

Electric-Light:

If it was that simple to implement, why do you think they don't just design motors like that? Do you think fitting refrigerators with US spec compressors for the Japanese market (100v) would decrease annual power consumption?

I do not understand your comment, and in particular relative to the device in the original post.

Motors and transformers are designed for some nominal voltage with some tolerance relative to the nominal value. In the design are such factors as starting torque, power output, temperature rise, duty cycle, efficiency, and others. In the application of a particular motor those factors and others pertinent to the application will be considered. In the past this design has been based on direct attachment to the supply line with no other electronic control.

This does not mean that in some applications one can not further improve the system efficiency by modifying the voltage to the motor.

Starting torque in a compressor application may be of prime importance, not efficiency. But once up to speed the input voltage might be reduced to improve operating efficiency over the majority of the on time.

If you look at power input to a refrigeration compressor there is initially a very large peak power requirement, then after the compressor is up to speed the steady state power input is high, but nothing close to startup. Following this it gradually drops considerably from the early part of the on cycle to the end. This implies a drop in load torque thru the on cycle. Thus, one could safely reduce the voltage during the cycle. From some data of 10-10-2009 on my Amana freezer I had an ON time of about 14 minutes, and an OFF time of about 30 minutes. Peak power averaged over 1 second at turn on was about 800 W, immediately following this the steady-state was about 400 W dropping gradually to about 330 W at the end of the 14 minutes. These are at 125 V.

In the design of a refrigerator there are large differences in steady-state line voltage that must be considered. The refrigerator will be designed to start at some minimum steady-state line voltage. This design criteria might be 105 V or even lower. Move this refrigerator to a location where steady-state line voltage is high, and there is excessive voltage for the motor's needs. Why not reduce the voltage if it improves the efficiency?

Also note that the power saving device is dynamic and self-adjusts to the particular conditions of both nominal voltage and varying load.

I think the question is not whether it works or not, but how much real improvement there is, and at what cost?

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[Electric-Light]

110415-2337 EDT

Electric-Light:

I do not understand your comment, and in particular relative to the device in the original post.

Motors and transformers are designed for some nominal voltage with some tolerance relative to the nominal value. In the design are such factors as starting torque, power output, temperature rise, duty cycle, efficiency, and others. In the application of a particular motor those factors and others pertinent to the application will be considered. In the past this design has been based on direct attachment to the supply line with no other electronic control.

This does not mean that in some applications one can not further improve the system efficiency by modifying the voltage to the motor.

Starting torque in a compressor application may be of prime importance, not efficiency. But once up to speed the input voltage might be reduced to improve operating efficiency over the majority of the on time.

If you look at power input to a refrigeration compressor there is initially a very large peak power requirement, then after the compressor is up to speed the steady state power input is high, but nothing close to startup. Following this it gradually drops considerably from the early part of the on cycle to the end. This implies a drop in load torque thru the on cycle. Thus, one could safely reduce the voltage during the cycle. From some data of 10-10-2009 on my Amana freezer I had an ON time of about 14 minutes, and an OFF time of about 30 minutes. Peak power averaged over 1 second at turn on was about 800 W, immediately following this the steady-state was about 400 W dropping gradually to about 330 W at the end of the 14 minutes. These are at 125 V.

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That's one powerful fridge you got there, unless its some sort of fast pull down commercial NSF rated model. Even at 70% efficiency, that's about 1/3 hp.
How big and old is that thing and what instrument are you using to measure true power?

Thermostats have hysterisis and I don't think two or three cycles is enough to really average it out. I think the freezer needs to be kept in climate controlled location and integration period should be about a week or so and running voltage needs to be precisely regulated during the duration of your experiment.

My service voltage averaged when I took a 30 hour measurement the other day, but the range of five-minute averages over 30 hour period was 122 to 126v.

The test would have to be done at 120.0v, 114.0v and 126.0v on a regulated power supply.

 

[gar]

110416-1049 EDT

Electric-Light:

The freezer is approximately 18 to 20 cubic-feet. 1/3 Hp is probably a good estimate. It is about 35 years old, and works great in very cold weather. It is in the garage, no heat. I have many days worth of data, and some of this includes both internal, and ambient temperature. Most of my tests are in the range of 0 deg F. The hysteresis is on the order of 7 deg F without digging out the data.

My line voltage is reasonably constant and I have data for this and whole house consumption for substantial periods of time. Days and months.

Most of the data is collected with a TED system. It is fairly good and the sample rate is close to once per second. So instantaneous power is measured and averaged for 1 second, then transferred to the computer. I can collect 24 hours worth of data at the 1 sec rate, and then it has to be saved to a file.

Once the freezer is stabilized, then the on-off periods are fairly consistent at a stable ambient temperature.

At some point I will get some of this data on my website.

Currently my experiments are mostly on house temperature measurements with one outside sensor, and nine interior. Three of the interior, each with a different configuration, are in front of a basement register to compare their response times in that air flow environment. In this application the sample rate is about once per two seconds.

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[Besoeker]

FWIW, I did the calculations on a 625kW motor for which I have good data on the equivalent circuit values.
Dropping the voltage by 10% reduces the losses a little at 50% loading, changes little at 75% loading and makes them worse at full load.
With a 20% voltage reduction, losses are hardly changed at 50% load, but greater at any loads above that.
The full load efficiency of this motor at rated voltage is 97.3% so maybe any departure from rated voltage might not have potentially the same benefits that might be obtained on other machines.