single phase motor power saving while idle

Most probably what this device does, is reduce the voltage from 234 volts to 158 volts. what concerns your energy savings you can calculate it with this formula disregarding the cosine phi factor.

Amps x Volts = watts

1.55x234=362.7watts this is the power consumption of 1 machine during sewing.

0.89x158=140.62watts is the consumption during rest

362.7-140.62=222.08 watts is what u save per machine

222.08x500=111040watts or 11.104 kw is your overall saving

thats quite something

222.08 / 362.7 = .61 = 61% of economy thats marvelous

Most likely, the device is based upon the "Nola circuit" invented by a NASA engineer named Frank Nola in 1969 to save energy on small single phase motors that were expected to be used on a space station eventually. In 1970 the technology was made widely available and became the basis for most of the electronic soft starter designs that are on the market today. Most soft starter manufacturers have eliminated that circuit as a feature however, because it really does not work well on larger 3 phase motors or if the motor has any kind of load on it. The reason this works in your application is that the motor is running unloaded. There are a lot of people trying to sell these things in applications where they claim the same kind of savings you have observed, but if the motor is not idle, the savings do not happen! The other thing to consider is, there is no better energy savings device than the OFF button!

What it does is to monitor the power factor of the motor because when a motor's connected load is removed or reduced significantly (at least 50%), the power factor gets lower and lower. Using this information in reverse then, the controller deduces that IF the PF is low, the motor MUST be unloaded, which means you will not be needing all of the available torque. It then uses SCRs to choke off the voltage (called phasing back the voltage) going to the motor. This reduces the magnetizing energy used by the motor, which is a parasitic load compared to the work load. This is where the extra energy savings comes from when comparing it to an unloaded motor without the controller. I'm glad to see that you did this comparison correctly, many people simply compare it to a LOADED motor, which means they incorrectly assume ALL of the energy difference is attributable to the Nola controller. They forget that ANY motor is going to use less energy when the load is not connected!

Phasing back the voltage also means that the available motor torque is reduced as well. Torque is reduced by the square of the voltage reduction, so in your case, the voltage reduction is 234 - 158 = 76V, / 234V = 32% reduction, so the motor output torque is reduced to .68 x .68 = 46% of normal torque. But because of the PF monitoring, the controller has already determined that the torque was not necessary anyway.

When the load is again applied to the motor, the PF goes up sharply, and the controller responds by quickly allowing full voltage through the SCRs, allowing full torque capability as well. Of course, at that point the energy savings stop.

So to recap, the additional energy savings that you observed are from a reduction in the magnetizing current (iron losses) in the motor, which can only be obtained at a cost of reduced torque, but as I said, the controller has already deduced that the torque wasn't necessary anyway.

If you Google "Nola Circuit" you will see a lot of information sites on this. Here is probably the best of them all.

http://www.lmphotonics.com/energy.htm

<if the machine is on for half an hour >

Each Machine working maximumum15 minutes,idling more than15 minutes-RIGHT?

<I wanted to know what is this device and how does it work >

Maybe an idleness sensor on foot swich off?-operating a switch to

either i) To a low feed voltage line

OR

ii) A Series Capacitor switched on to improve factory load Power Factor better at the same time

Your Q<how much units of electricity I would save in a hour of off load operation on 500 such machines> can be replied with a little accuracy only if you tell us:

Power factor cosØ in both conditions<1.55amperes 234 volts .89 amperes 158 volts>

I am showing my ignorance here. All the sewing machines I am familiar with are small home style machines and light industrial machines. When they are not sewing they are OFF or zero power. When they are stitching they are ON.

Do your motors run continuosly when not stitching and clutched in and out mechanically?

Just curious.

The Machines he is talking about have a single phase motor below the table which runs all the while with a simple cluch which is engaged to power the sewing machine head via a belt drive. These are an older style of machine manufactures like Brother have have moved towards starting and stopping the motor but the problem is then producing enough torque from startup to start sewing especially when sewing thick fabric or leather.

Sounds like a good application for a VFD or small DC drive. But then project would take a couple years to have a payback.

Did anyone warned you against possible locked rotor situation? It is unhealthy to reduce the voltage on any AC motor by more that 15%, and let it idle. Just switch it off. it's the best that you can do for your motor. Your supposed savings will be lost in heat anyhow.(if not at smoke) Single phase motors are inefficient enough, don't make their life any harder.

Wangito.

But Wangito,-the Questioner's 500 motors never locked.They run idle-declutched.

The process probably demands- they keep running at full speed.

That points to my #2 possibility.

BR

MM

The Nola controller only reduces the voltage when the power factor is low. If the rotor were locked, the power factor would be at it's peak! While I agree that the Off button is the world's best 'energy saver", it sounds as though this application is one of those rare occasions where the Nola controllers may actually provide a benefit.

Download Nola Device Overview