electric motors


Postby livewire » Sat Aug 22, 2009 5:20 pm

hi

I was helping someone fit electric blinds at Media cityUK in Salford yesterday and would just like to understand a little more on how they work basically. Ok, you may find a picture of the blinds: Google "levolux.com/L_products/internal_blinds.htm" here if you wish.

They operate via an electric motor, naturally; but a four core cable is used underneath it all! I asked the electrician: "how do they work then?" He said: "We have four cores; one takes the blind up; one takes it down; the neutral is shared; and the final core is used as an earth."

I'm thinking all kinds of questions now, A motor can only do one thing at a time?; it's either going up or down (forward or reverse) ok, seems logical; but how do i translate or interpret a current doing some work either up or down or forward or reverse? Does anyone have an understanding of electric motors?

I appreciate it's a bit of specialist area, but I have to understand how things work.

help please.
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Postby kbrownie » Sun Aug 23, 2009 6:33 pm

The motor will work so when swirched to go up it goes up and when switched go down goes down. You know that so how does it do it.
The switch will allow reverse rotation by reversing the connection to either the start or run winding.
If you google AC single-phase motors you may find a more elaborate explaination
KB
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Postby kbrownie » Sun Aug 23, 2009 6:34 pm

Please Google"allaboutcircuits.com/vol_2/chpt_13/9.html"
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Postby livewire » Mon Aug 24, 2009 12:42 pm

[quote="kbrownie"]Please Google"allaboutcircuits.com/vol_2/chpt_13/9.html"[/quote]

thanks KB, complicated - i did ask i suppose. ;)
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Postby livewire » Mon Aug 24, 2009 12:53 pm

[quote="kbrownie"]Please Google"allaboutcircuits.com/vol_2/chpt_13/9.html"[/quote]

EDIT:

Its the four core cable i'm trying to get to the bottom of. Does this

Google "tpub.com/content/neets/14177/css/14177_88.htm"

explain why we use four core for this kind of circuit? Two phases, one neutral and an earth?
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Postby kbrownie » Tue Aug 25, 2009 9:34 am

Not clearly,
Motors can be a complexed thing to explain,
I'll try find some working models for you to view on the internet. I'm sure there are some?
The motor you are questioning will work using a pulsating magnetic field.
The four cables will work as so;
earth and neutral do what they always do a protective conductor and a return for the current to travel via the neutral.
The two line conductors will still be single phase but one will opereate the forward motion of the motor when switched ie wired to one side of the start winding
and the other one will be connected to the opposite side of the start winding so the motor goes in to reverse when switched.
Basic explaination but hope it gives you an inkling.
KB
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Postby livewire » Tue Aug 25, 2009 6:39 pm

that's clarified it pretty much! Very interesting KB, thanks again... :)
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