Controlling the speed of an AC motor using a PIC mcu?

[lurkepus]

HI
I'm currently working on a project witch wil require controlling the speed of an AC motor .

The setup is something like this .. a thermocouple is used as a temp sensor feeding the temp to a PIC mcu.( the sensor could be any type of sensor thermocouple is just use as an example)

The rpm of the motor should be adjusted according to the settings programmed into the mcu .

I have done some reading about the subject of AC motor controll and i know i need to adjust the frequency so a pwm /ssr solution wont't work .

So what is the simplest way to controll an AC motor using sensors and a PIC mcu?(the motor could be anything from a small 300watt single phase to a much bigger 3 phase motor .. )

 

[Wond3rboy]

Hi, i believe a triac /triac combination could be used to do this. Rating will need to be more specific though.

 

[lurkepus]

Thanks for the answer Syed ..

I don't have a spesific Rating in mind but let's say 1.5 kw@ 220/240 volts single phase motor for the fan i guess it will be the bigest single phase motor i'm going to use .. Not sure about the 3 phase motor but for the sake of argument it will be a 4 kw @220/240 volt motor.

Another feature witch would be nice to add in is the possibility to change the rotation from CW to CCW

Btw wont a triac just behave like a solid state relay?? I know they aint good for altering speed og an AC motor.

 

[Nigel Goodwin]

You need to specify the exact type of motor, universal ones can be easily controlled, many AC only ones are FAR more difficult and expensive to control.

 

[lurkepus]

I was thinking about using a asynchronous ac motor but i'm in the planing stage so i can go with any typ of single phase AC motor.. any suggestions ???

 

[Nigel Goodwin]

I was thinking about using a asynchronous ac motor but i'm in the planing stage so i can go with any typ of single phase AC motor.. any suggestions ???

I would suggest buying a motor complete with speed controller, making sure it's one you can easily control from a PIC.

 

[lurkepus]

I found this Microchip App note maybe it can be of any help ?? i haven't had much time reading it but i will ASAP

 

[lurkepus]

Thanks for the suggestion Nigel .. i just have to find the right motor with the type of speed controller... btw when it comes to the speed controller are there any type in perticular i should bee looking for ??

 

[be80be]

These https://www.electro-tech-online.com/custompdfs/2012/02/gs1drives.pdf would be nice to play with.

 

[lurkepus]

thanks Burt.. i notice it has a usb and ethernet as an option do you think it could be controlled by a pic with a usb or ethernet connection ?? .

 

[be80be]

USB no Ethernet is doable But I would go with RS232 or the 485 The data sheet said it could use them too $99.00 and you can use 1/6 to 1/2 I think but there are bigger ones. 100 hp and up I did have some but there gone now.

 

[lurkepus]

since this is a part of a larger project i think RS232/485 would be what i'm looking for i might get one of the smal once and do a test.. i just need to find a Norwegian supplier.. i also need to do a lot of reading so i guees i know what i will be dooing the nex couple of days

 

[lurkepus]

i had a look at E-bay to see if i could find a cheap solution for testing but even on ebay they are expencive .. where did you get the drive for $99 ??

 

[shortbus=]

Those drives are only for three phase motors. So far there have been no vari-speed drives for single phase motors. A single phase motor uses a separate 'starting' winding, since single phase won't create a "rotating magnetic field" by its self.

 

[be80be]

Read the data sheet it work with single phase but you have to use a three phase motor

 

[be80be]

If you new what kind of motor there are a lot of options here

I would use a DC motor there made for this kind of thing and have lot more torque

 

[lurkepus]

I could use a DC motor for the fan but will a DC motor have the same torque as an AC motor in the same price range ?? i know i will need more motors for this project .. one will be used for a smal shredder i also need one for a feeding auger..

 

[be80be]

find what hp you need

 

[shortbus=]

Read the data sheet it work with single phase but you have to use a three phase motor

Reread my post, thats what I said. "Those drives are only for three phase motors", said nothing about not being powered by single phase.

 

[be80be]

Nope but you didn't say it could power a 3 phase motor from single phase power the OP could find some cheap 3 phase motors and run them off single phase power with these save having to have 3 phase power.

I didn't want them to think O hell I only have single phase

And there are some single phase motors that can be used, Not with this controller there a m31 type I think that's right Haven't been doing any of this in years

And the reread was to make sure no one missed any thing.