Energy saving device for freezers

[Dave_G]

Hi,

A while ago I was watching TV prog' and I can recall some type of plug that you fitted to fridge/freezers that reduced the use of electricity - I seem to remeber they were 'smart' in that they allowed the freezer to power up only when required?

Can anyone help me find these?

Thanks,

David

 

[Alf]

Savaplug?

 

[Dave_G]

Thanks Alf - the link is very helpful... seems like 'snake oil' :shock:

 

[Jake]

Not all electronic engineers agree with Tony on this - try a search on uk.diy in google groups, and you'll see that one or two took a look at the literature put out by Savaplug and thought that there was a rational explanation for the claims made. The DTI obviously does as well, for what that is worth.

 

[RogerS]

The DTI obviously does as well, for what that is worth.

Ah well..that answers that then, doesn't it :wink:

 

[WoodPecker]

From the Savaplug site:

HOW DOES IT WORK?
When the thermostat on the appliance switches on the motor to pump the refrigerant around the system full power is required to start the motor. However, once the motor is running full power is no longer needed.

The SavaPlug senses this and reduces the flow of electricity to match the actual requirements. When the red light glows savings are being made.

What they are claiming is a load of what bulls make :shock: The first section is correct except that they have neglected to mention is that once the motor is running at full "speed" it won't concume the same amount of "power" anyway as the current required to keep the motor running will be much less than at startup. A load only draws as much current as it needs, they are suggesting that the motor continues to draw the same amount of current after startup as during startup and this is complete BS.

 

[ike]

An auction channel perchance? If so, the price should bid down to nothing cos that's all it will save you :lol: .

cheers,

Ike

 

[Jake]

I think it is possible that this is too simplistic a view.

Electronic controls can improve electric motor efficiencies. See for example:

http://www.ecnmag.com/article/CA433417.html

Fridge motors are vastly overrated for their normal running load, because they need to start into a fully compressed load. From what I've read, most (eg workshop) compressors discharge the compression chamber when the motor cuts out. Fridges don't do this as it would add a potential leak into the system. So they have to overcome a good deal of torque on starting up - you can see the lights dim sometimes. That means they have to be vastly overrated for the running load. From there, back to the article above. I guess Mr Godbole is selling stuff, but is he full of bs too?

As I understand it most modern fridges and freezers have this stuff built in already to get their higher energy ratings, so adding an external one will not help and may do harm.

 

[Anonymous]

Save your money.

The SavaPlug senses this and reduces the flow of electricity to match the actual requirements.

What utter and complete rubbish. The motor itself will draw less current once the initial starup torque has been generated to overcome the striction and frictions in the system.

"Match the actual requirements"??? Doesn't this sentence say it all? The device will do nothing as the motor will draw the current it requires

The phrase "reduces the flow of electricity" is meaningless too - current flows, not electricity!!

This device will only make you poorer - by £20.

 

[Jake]

device will do nothing as the motor will draw the current it requires

So Mr Godbole is talking out of his rear-end?

 

[AndyBoyd]

As a senior engineer working for a very large oil company with PhD in physics I feel a lesson comming on. :roll:

We do this with our large motors/compressors when they run in steady state, we actually reduce the power to them by removing some of the sine wave of the AC (three phase or single phase). The motor pulls more current when we do that to compensate but the overall power consumption is less as we are basically reducing the voltage (hence the motor rotates slower) - but this is averaged down over time so can be hard to get your head round it.

This can realise up to 20 % power consumption savings at steady state (of course motors are rarely run at steady state so the actual total saving is circa 5%). But as we run massive motors this is a consierable cost saving for us.

So I think they do that, the trick is we have very smart system to detect when we can do this and when we need to turn it off, I'd be interested to see how savaplug senses that. (Our sensing systems are very expensive)

I've just checked this with our electric engineering gurus (literally round the corner from me) and they confirm the above

Old fashioned drill speed controllers work in the same principle

 

[ike]

Tony wrote:

This device will only make you poorer - by £20

Totally agree, but just think of the massive savings!... erm that'll be bout £2.50 a year then?.. :roll:

A case of "if something sounds to good to be true, it usually is" I suspect. :lol:

Ike

 

[Jake]

That's £2.50 more a year than it was a few hours ago. At this rate a savaplug will be earning cheques from the lecky company by tomorrow evening!

 

[ike]

That was based on your 5% saving!

 

[Anonymous]

Andy

Zero crossing phase delay triggering (which you describe) can be done quite cheaply if one is not looking for a sophisiticated system capable of controlling and monitoring a large motor.
If we assume the supply is steady 50Hz, we can simply wait for a small period (a few hundred microseconds) after the zero crossing point in the sinewave and then turn the switching device on.

I have designed many motor speed controllers using a similar principle in my 20+ years as a design engineer, mostly using cheap microcontrollers.

However, I still see no saving on a small motor which runs on low load.

 

[omega1]

Hi
Just been readding your post about the control of large AC induction motors, I always believed that the speed of rotation was governed by the number of poles and the frequency of the supply, or are you using other types of AC motors?

I thought that fridge compressors were run by induction motors.

Regards karl

 

[Jake]

That was based on your 5% saving!

Not mine...

 

[Jake]

I have designed many motor speed controllers using a similar principle in my 20+ years as a design engineer, mostly using cheap microcontrollers.

However, I still see no saving on a small motor which runs on low load.

Mr Godbole or whatever his name seems to have at least equal experience but appears to disagree though? Is he just talking about more sophisticated techniques or something?

 

[AndyBoyd]

Tony - you must be right, we apply this technique and a few other very fancy ones :wink: on motors larger than your house.

 

[CHJ]

Hi
Just been readding your post about the control of large AC induction motors, I always believed that the speed of rotation was governed by the number of poles and the frequency of the supply, or are you using other types of AC motors?

In an ideal world it is, (a motor running with no load). However in the real world there is a certain amount of 'slippage' as the rotor tries to align with the next pole in its path (think of the magnetic connection as an elastic band that gets distorted as load is applied)

I think that what is being described is managing this 'slippage' by reducing the supplied energy without the rotor getting too far behind the poles and stalling. (done at the phase crossover point to reduce heat in control components because you are switching off power at it's least effective point) (Tony?)

I thought that fridge compressors were run by induction motors.

They are.