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Posts Tagged ‘Electrical’

Electrical resistance of Kundan, Orbit insulated wires

October 3rd, 2017 No comments

When the electrical resistance of the copper cable is high, the possibility of power loss is higher leading to heating and melting of cables.  So, I decided to measure the actual resistance of commercially available electrical cables with three different cross-sectional areas.

1 sq.mm 1.57 Ω @ 30℃
Kundan 1.8 Ω
Orbit 1.8 Ω
2.5 sq.mm 0.628 Ω @ 30℃
Kundan 0.7 Ω
Orbit 0.9 Ω
4 sq.mm 0.392 Ω @ 30℃
Kundan 0.6 Ω
Orbit 0.7 Ω

From the analysis, “Kundan” seems a better choice.

Ref: http://hyperphysics.phy-astr.gsu.edu/hbase/Tables/rstiv.html

Understanding a Fan Motor

August 28th, 2012 4 comments
Have you opened up a fan motor before?  It is a simple brush less A/C induction motor, where the armature remains as the stator.  Look at the exploded image of a typical fan motor. The important parts are C: Ball Bearing, D: Stator, E: Armature/Stator, G: Capacitor, H: Connector. 

Also, look at the other image that shows the cross section of a motor.  You would notice that there are 4 wires coming out the motor.  Two pairs of wire, with one pair as the starting coil and the another pair for the running coil.  In general, all single phases induction motors have two coils (starting coil, running coil).  Using a capacitor, an artificial phase difference is created between the fields created by the starting and running coils.  The phase difference triggers movement of the armature.  When the armature reaches a particular speed, using a centrifugal switch, the connection to the starting coil is disconnected and the entire fans runs with just one coil.

Although there are four terminals, you would notice 3 terminals are emitted out, with the starting and running coils connected back-to-back.  Let’s say S1,S2 are the terminals of starting coil and R1,R2 are the terminals of the running coil.  To get 3 terminals out of the fan motor, S2 and R2 are shorted. 

Now, you just see 3 terminals; how do you find which terminal is starting, which one is ending and which one is shorted?  Easy.  Using a simple multimeter, you can find it out.

Let’s say you see terminals A, B, C. Our aim is to find which one of these are S1, R1, S2R2.  Now, let’s measure the resistance between A-B, call it X.  Likewise measure the resistance B-C as Y and A-C as Z.  If you would notice X < Y < Z, you would also notice that Z = Y+X.  Which mean, A-C is action A-B+B-C, that’s why the resistance was additive, also the terminal B is S2R2.  The challenge now is to find what is A and what is C.   As we’d notice A-B=X < B-C=Y, we can confirm that terminal A is starting coil S1 and terminal C is running coil R1.  The reasoning is that; starting coil resistance will be less than running coil resistance.

Hope, this article helped.

Another Automation Project

May 2nd, 2009 No comments

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