Author Topic: will this setup work? (Read 4215 times)

seth526 · « **on:** December 28, 2012, 12:53:23 AM »

Hello Friends,

I am new to this topic,if i am asking something stupid please ignore.

I have attached an image which shows that there are 4 permanent magnets with alternate poles on the 4 sides of a rotor.When i supply current to the 2 coils will it rotate the rotor or not.

If not,then why?

Flux · « **Reply #1 on:** December 28, 2012, 04:47:53 AM »

Depending on the direction you wound the coils, it will either stay still ( coils attracting magnets) or rotate 90 deg to reach the same state.

Once it has rotated that 90 deg you need to reverse the connections to the coil and then it will go another 90 deg aand then you need to rteverse again.

In days of old before electronics the only way was with a commutator and brushes and that method still works today. For those brought up in the space age you can use electronic switches ( mosfets , transistors or similar ) and you need something to tell it when to switch ( hall sensors or opto sensors or obtain feedback from the emf induced in the coils.

Don't try to invent the wheel , just look up electric motor. Alternators don,t run off batteries as motors.

Flux

seth526 · « **Reply #2 on:** December 28, 2012, 11:44:28 AM »

Thanks Flux for your reply , if instead of DC we supply AC to this setup will it rotate.

dbcollen · « **Reply #3 on:** December 28, 2012, 12:22:53 PM »

yes, it should motor, but you may need to spin it to get it to start.

Flux · « **Reply #4 on:** December 28, 2012, 12:41:40 PM »

That's right, you WILL need to spin it to start and it will only rotate at one speed where the ac polarity is reversing at the speed the magnets are swopping over. This is the synchronous speed and for a 4 pole machine like you have drawn that speed will be 1500rpm on a 50Hz supply or 1800rpm for 60 Hz.

What you have invented is a synchronous motor, try looking that up.

Flux

seth526 · « **Reply #5 on:** December 29, 2012, 01:33:48 AM »

Hey Flux,

Thanks for your reply friends.Please don't say that i have invented something.I know my questions seems to be stupid to you,but i don't have this knowledge, that is why i thought of asking on this forum.

I will try with AC and let you know about the results.One more thing friends if i attach a start capacitor, still i need to spin it or it will rotate by itself.

Flux · « **Reply #6 on:** December 29, 2012, 03:55:55 AM »

Synchronous motors are not inherently self starting even on 3 phase with a true rotating field. Using a capacitor to produce a partial 2 phase is similar and a bit less effective.

The usual options are to include some form of cage winding to start as an induction machine or to raise the speed from standstill by feeding with a variable frequency inverter.

Tiny motyors such as used in clocks will sometimes start by inducing the rotor to vibrate and if the amplitude can build up enough it may lock in step. Such motors have a large number of poles, a 4 pole machine won't start that way.

Flux

seth526 · « **Reply #7 on:** December 29, 2012, 10:18:19 AM »

Thank you very much Flux,I have done right thing by joining this forum.

I am not done with my AC setup till now,once done i will let u know the results.

seth526 · « **Reply #8 on:** January 19, 2013, 02:11:46 AM »

Hello Flux,

I am finished with my AC setup,but i am facing some problem.First thing is its not rotating, a small jerk is coming and then its stopped.And next point is the coils are getting very hot.

Am i doing something wrong?Please advice me.

Flux · « **Reply #9 on:** January 19, 2013, 04:09:01 AM »

I really have no idea what you are trying. You have only shown basic theoretical sketches. To make a practical motor you will need proper iron circuits to contain the magentic flux.

If you are trying with the simple open coils that you show you will need very high currents to produce enough field to sustain rotation. If you get it to work at all it will be as a toy and it will not produce real torque. you will need very free bearings at least.

There is a large difference between the theoretical diagrams for electrical machines and the details of a working motor.

As a boy I used to make simple electric motors with a coil wound round a cork. the end leads were left sticking out to act as a simple commutator and another pair of springy wires touched them. The magnets were from moving iron loudspeakers of the day. A needle through the cork acted as a shaft and ran in light brass strips, it was all very free turning.

With care I could get these to run fairly well, but it will be more difficult to get the ac version to work where you have to get it in exact synchronism with the supply.

If you atre trying to make a serious motor you will need to produce something much more complex than those sketches

Flux

tanner0441 · « **Reply #10 on:** January 19, 2013, 08:38:59 AM »

Hi

What you show in your diagram is basically a 90 degree stepper motor, so if it jerks through 90 degrees every time you revers the supply then it is doing what it should.

Follow flux's advice and read up on electric motors.

Brian.

tanner0441 · « **Reply #11 on:** January 19, 2013, 08:47:01 AM »

Hi

What I forgot to add was with only one winding there is no control over which direction it turns.

As a PS also read up on basic alternating current theory, so you can appreciate it when people talk about phase angles and rotating magnetic fields.

Brian

OperaHouse · « **Reply #12 on:** January 19, 2013, 09:16:38 AM »

This is exactly the design of most washing machine pumps today. The impeller is designed to work in either direction. I had an electric can opener with the same type of motor. It had a cogging device that prevented rotating in the reverse direction.

seth526 · « **Reply #13 on:** January 19, 2013, 11:45:38 AM »

Thanks all of you for your reply's ,i am attaching a pic that will give an idea what i have done till now.

Brian its not even moving 90 degrees.

Does the coils in series or parallel makes any difference?

Flux · « **Reply #14 on:** January 19, 2013, 12:33:45 PM »

It is basically as shown in your original sketch. The coils are tiny and don't seem to be well lined up with the magnets.

It doesn't matter in theory whether the coils are in series or parallel but they must be phased to produce the correct polarity.

It is more usual to use 4 coils for a 4 pole rotor and again the coils need to be connected tp produce the correct magnet polarity ( N S N S). That set up looks to have a lot of inertia and you will need a lot of effort to spin it up to synchronous speed !500 rpm 50Hz or 1800 rpm 60 Hz. Your bearing and windage loss may be more than the small field from your coils can support.

I am not at all convinced that you will get it to work with open coils, the best chance would be with larger coils which will let you use thicker wire for the same number of turns and you can push the current up.

The field produced by your air coils will be small, with an iron circuit you can reduce the reluctance by a factor of 1000 and get more working flux.

Flux

tanner0441 · « **Reply #15 on:** January 19, 2013, 01:32:24 PM »

What are the coils mounted on? Is it wood or are they ferrite formers?

Brian

seth526 · « **Reply #16 on:** January 20, 2013, 02:48:29 AM »

Brian coil are mounted on wood.Each coil is 250 turns of 20 no. wire.Do i need to increase the size of coil?

OperaHouse · « **Reply #17 on:** January 20, 2013, 06:05:09 AM »

Having a magnetic path between the two coils will greatly increase the strength. Both coils must be in the proper phase. Just think if one coil is attracting and the other is repelling the rotor, there is no effective force.

seth526 · « **Reply #18 on:** January 20, 2013, 06:31:19 AM »

I have read somewhere if i give supply to both the coil in parallel then either north or south will be produced in both the coils, do u mean the same by putting the coils in proper phase.

XeonPony · « **Reply #19 on:** January 20, 2013, 01:38:12 PM »

http://www.allaboutcircuits.com/vol_2/chpt_1/1.html

http://www.johnsonelectric.com/en/resources-for-engineers/motors/basics-of-motors/ac-motors-theory.html

Do you not get google or other such search engines in India?

hiker · « **Reply #20 on:** January 21, 2013, 01:12:48 AM »

might help...................
http://www.google.com/search?q=homemade+motor&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a

News:

Author Topic: will this setup work? (Read 4215 times)