OT Power consumption in AC motors

PeterH_DK

Member
Join Date
Jan 2006
Location
Copenhagen
Posts
17
Sorry guys,



This is totally off topic, but never the less technical.



I have been following this site and received fast help a few times concerning my own plc problems, and I have been astounded by the immense amount of technical knowledge here. so I'll risk my neck with an OT question:

I have been asked to help out a friend who wants to market a power saving product., that should be able to reduce power consumption on AC motors by up to 40%. www.somar.co.uk



The product is built on the claim that “a 300 watt motor will draw 300 watts regardless of the load on the motor” Is this correct? I just don’t know enough about motors to judge that.

Somar claim to be able to “sense” the load of a motor and regulate the energy accordingly.

Does this make sense?

/Peter
 
PeterH_DK said:
The product is built on the claim that “a 300 watt motor will draw 300 watts regardless of the load on the motor” Is this correct?

No.

Imagine a 300 W motor (about 1/3 hp) for your furnace fan. Now, imagine disconnecting that motor, and putting the fan blades from you bathroom vent fan on its shaft. Do you really think it will still take as much energy? Of course not!

I get a distinct feeling of snake oil from this one. They never really describe how their "technology" works, just that it will reduce power consumption. When you combine the lack of technical detail with clearly incorrect information their credibiltiy gaps.
 
Considering that most motors above a few kW are already quite high in their efficiency rating, there is not that much wasted power to recover.
Unfortunately, there is always someone touting an impossible scam somewhere, and if it sounds to good to be true, it probably is.
 
I never saw in their site where it says a 300 watt motor always pulls 300 watts. That is not true (as has already been said).
After looking at it a little, it looks like they are in effect reducing the voltage when the system demands a lower load. Would this offer any savings?


I'll have to think about this more when I get a chance - or I can just wait and read what everyone else has to say since there are plenty of technically sharp people here.
 
I just had a look at the web site, and none of the claims seem to be outrageous. However, there is also no real outline of how they do it.
It seems to be ordinary matching of the load with a VSD, which would probably decrease efficiency unless you are doing a lot of starting and stopping.
More people are now becoming aware of the importance of energy efficiency, without knowing too much about it. This means that there are plenty of opportunities for con artists.
Either that, or the web site was badly laid out to give the impression of the old smoke and mirrors trick.
 
I remember a company called MTE sold us some soft-start units for some 15kW motors some 15 - 20 years ago. They said that the unit would adjust the voltage output to suit the load drawn and would therefore reduce energy consumption by up to 40% for a fan with a modulating damper typically running between about 50 - 75% capacity (can't remember if those figures were exactly what was quoted but they were in that ball park). Never heard back from our customer to see what results they had.

Was this just sales blurb or did it save energy, I wonder?

I do know that a controlling air flow from a fan using a VFD is far more efficient than using a damper and it always amazes me how customers are reluctant to spend that bit extra on a VFD, despite environmental issues and energy prices being high on the agenda these days.
 
I've got a bunch of AB SMC starters that have an energy saver mode - reducing voltage to the motor when it is idling. These units are up to 16 or 17 years old. Nothing new there.

I didn't see any claims about how much energy their product would actually save.
 
My undergraduate project (1981) was a microprocessor based three-phase thyristor controller (a big dimmer switch) connected to a lightly loaded induction motor. As the voltage was reduced from maximum, the current would fall and then start rising again - my algorithm used "hill climbing" to find the minimum current point - just remenising really !
 
There are a BUNCH of "soft-start" type controls that actually reduce the motor voltage during periods of LOW amp draw. This will reduce the power consumed.

However, during periods of LOW amp draw, the power drawn by a motor across the line is actually reduced. NO motor draws FLA at light loads. Some low base speed motors will draw higher amps but they also are HIGH torque devices.

Additionally, some of these energy saving devices also add some power factor caps and filters.
 
What's really happening here is that the electronics sense a light load and reduce the voltage to reduce the magnetizing current. The logic is ----why fully magnetize a motor when ist is not developing full torque.

It is true that some energy can be saved if the motor spends long periods just idling along---about 2% max. Hardly worth the trouble in most cases.

You pay a performance penalty to do this. The motor, after running in this light load-low voltage mode, needs a second or two to remagnetize so, if your application requires fast motor response to a sudden increase in load, its not a good idea. Especially for 2% max.
 
It is very useful topic for me, nowadays many companies say that manufacture motor energy controller (MEC), any body really used them? If yes what is result?



Regards.
M.J.Danesh
 

Similar Topics

I was wondering if anyone had any insight on to how i could monitor and possibly graph Amp draw on our Powerflex 525 Drives. These drives are...
Replies
5
Views
1,700
Hello, I want to ask about the power consumption of the 1769-Pb4: It is written that the input power consumption at maximum load is equal to...
Replies
1
Views
1,797
Hi All, I'm having some trouble on determining the total power consumption of the following I/O modules: 1769-OB32,1769-OF8V, 1769- OW16...
Replies
1
Views
2,573
Hello We have a 3 phase machine where we need to log the power use during every run of a process. Each run can last anywhere from 30min to 5...
Replies
4
Views
2,269
Dear, I am computing a rough estimate on the power consumption for UPS for a PLC cabinet, the UPS will be also serving two flowmeters (each...
Replies
1
Views
1,567
Back
Top Bottom