Single phase amp reading. 1

[WardHollowayPE]

I have a small single phase motor with no name plate. I want to use a variac transformer to control speed, so I want to read amps while it is running but I don't want to cut open the cord. Question.. can I get an accurate reading from around the entire cord? This includes live, neutral and ground. The reading I get around the cord is almost five amps. Should I size a larger variac or will a five amp suffice?

Ward Holloway, Jr, PE

 

[LionelHutz]

Honestly, I wish you luck...

An AC motor want to run at a speed that = freq x 120 /#poles.

This means you need to vary the frequency to control the speed.

If you just reduce the voltage the motor will still want to run at rated speed. But it won't be capable of producing rated torque. So, as you apply load the motor will start to slip and slow down but the slip is very uncontrolled so you'll have no real control and the speed will likely vary A LOT as the load changes or as the line voltage fluctuates.

A fan has a load torque that increases with the speed^3. So, if you build the motor right you can make the speed controlled via the voltage. As you increase the voltage you get more torque which allows the motor to turn the fan faster. Works well. Unfortunately, your conveyer will have the same torque requirement at all speeds - it's not likely to work well at all. Reduce the motor torque and you'll be all over the place speed wise.

 

[stevenal]

"I will attempt the variac solution as many post indicate this will work with a shaded pole motor."

I don't see these posts. Did they get deleted?

Please change "Your" to "You're" in my previous post.

 

[itsmoked]

Does this help stevenal?

There are a few types of 1 phase motors that can be controlled by varying the voltage; the Universal motor as Marke said, and the [red]Shaded Pole motor.[/red]

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[Skogsgurra]

That doesn't say that a conveyor can be speed controlled using voltage control.

A fan, yes. A conveyor - no. No way.

Why don't people listen...?

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[itsmoked]

Now Skogs... Did you not try a few stupid things after your parents told you that it was stupid/dangerous?

It could actually be a conveyor that moves feathers one at a time and so some setting will actually work. The OP isn't clear on the configuration.



Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[jraef]

I agree. Although I said a shaded pole motor can be controlled with voltage only, I have never seen one used on other than a fan. The classic example is the paddle fan on your ceiling.

That must be one tiny little conveyor... moving pimentos into an olive stuffer perhaps?

 

[Skogsgurra]

Pimentos or feathers... The conveyor will still be either running or standing still. Maybe, there is some voltage that will make it run at some intermediate speed. But come sun (or come rain) and that speed will change.

Yes smoked, I tried making black powder. Several times, actually. And suddenly - it worked. That's how I lost my hair. First time.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[stevenal]

itsmoked,

No it doesn't help, since in his same post jraef said "Unfortunately Shaded Pole motors are almost completely useless when it comes to putting them on conveyors."

Still can find only one post that recommends he try this, and that one only suggests he try it to show it won't work. Hardly qualifies as "many."

 

[WardHollowayPE]

It is a shaded pole motor about ,7amps. It is on a conveyor.
I decided to try the Optidrive or something simular.
Thanks for the help

Ward Holloway, Jr, PE

 

[WardHollowayPE]

Update...
I called the Optidrive vendor and as soon as I told him what I was doing he almost refused to sell it to me. I also researched replacing the motor-gearbox and found out it's a custom designed unit for this conveyor. It appears my only option is to replace the motor-gearbox and design a custom mount for it. I may not have the time for this.
If anyone has any ideas for speed control of the original motor please post it.
Thanks

Ward Holloway, Jr, PE

 

[sreid]

Can the motor and gearbox be separated? If so, the motor is almost certainly a standard frame size. If not, you may be able to buy a three phase "Frameless" replacement.

 

[itsmoked]

Being really small, as conveyors go, maybe you can just get a large stepper motor or servo motor and some inexpensive off-the-self controller with a pot adjustable.

Strap the direction and feed in any speed pulse you want.

http://www.geckodrive.com/

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[ScottyUK]

Use a PM DC motor? This is well within the power requirements for this type of motor and it is easy to vary speed of them.


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Sometimes I only open my mouth to swap feet...

 

[Marke]

With a shaded pole motor, reducing the voltage will educe the torque capacity of the motor. If you reduce the torque below the torque required by the load, the motor will begin to slow and will continue to slow until the torque of the load falls below the torque produced by the motor.
With loads such as pumps and fans, the torque increases as the speed increases and so the reduced torque will cross over the load torque at some speed. This is what determines the operating speed.

With the conveyor, the speed torque curve will be very different, however if the torque does increase with speed, then there may be some potential for variable voltage control.
With torque control on an application where the load torque may change with load, the speed will change with load.
Speed stability could then be improved by the addition of some form of speed feedback and PID control, but at the end of the day, it is probably going to be cheaper to fit a three phase motor and three phase speed controller.

Best regards,

Mark Empson

http://www.lmphotonics.com