# how can be ac load current and resistance calculated

Discussion in 'General Electronics Chat' started by fayazahmedmemon, Jul 9, 2010.

1. ### fayazahmedmemon Thread Starter New Member

Jul 4, 2010
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how can the load current taken by the ceiling fan or 100w bulb be calculated if the AC input is 220v. can we calculate the resistance of Ceiling fan and 100 watt bulb?

2. ### Jony130 AAC Fanatic!

Feb 17, 2009
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1,272
hmm, P = V* I ---> I = P/V

3. ### mcgyvr AAC Fanatic!

Oct 15, 2009
5,395
1,196
Easiest is to just read the watt rating on the nameplate on the ceiling fan or the rating on the lightbulb.. This will get you pretty close. Now sure how close you need to be though.

But using Ohms law. 100W/220V=.45 Amps at 120V it would be 100W/120=.83 Amps

4. ### Jony130 AAC Fanatic!

Feb 17, 2009
4,508
1,272
And Bear in mind that resistance of a light bulb is highly nonlinear.
See the graph of resistance of a 100W/230V
light bulb in function of a supply voltages.
Resistance for 230V is equal 530
Ω so current is equal 0.434A
But for 120V the current will be equal:
I = 120V/ 380Ω = 0.315A

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5. ### debjit625 Well-Known Member

Apr 17, 2010
790
186
Very simple use a Amp meter.Now for the bulb the resistance is constant so using ohms law will do the job .But for the fan its not so simple because the fan is made using coil i.e.. inductor and also its run under singal phase so we add a capacitor to make two phase ,Now we could see that ,its a inductive come capacitive circuit so the the total impedance is the resistance here.Its calculated using Complex numbers which is quite different then scaler calculation.

Good Luck

6. ### fayazahmedmemon Thread Starter New Member

Jul 4, 2010
15
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Thanks for idea but sir how can be the wattage rating of fan calculated because it is inductive load and what is apparent power

7. ### fayazahmedmemon Thread Starter New Member

Jul 4, 2010
15
0

Thanks a lot sir.Sir can we say that the resistance of bulb varies due to the varying ac voltage therefore it is nonlinear resistance.

8. ### fayazahmedmemon Thread Starter New Member

Jul 4, 2010
15
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Thanks for such a nice guidance.Sir can we say that the fan and capacitor make a LC circuit.

9. ### mcgyvr AAC Fanatic!

Oct 15, 2009
5,395
1,196
No.. the filaments (the part of a lightbulb that glows) resistance changes depending on its temperature.

10. ### debjit625 Well-Known Member

Apr 17, 2010
790
186
Yes it forms a LC circuit,Google about "poly phase ac induction motors" .The motor have two coils (in real many all interconnected to form two coils) 90 degree apart from each other and connected in series with each other and the capacitor is connected in parallel with these coil.

I am just a student ,so no Sir just debjit625

Good Luck

11. ### fayazahmedmemon Thread Starter New Member

Jul 4, 2010
15
0

Thanks a lot Sir

12. ### fayazahmedmemon Thread Starter New Member

Jul 4, 2010
15
0

Thank a lot Sir

13. ### fayazahmedmemon Thread Starter New Member

Jul 4, 2010
15
0
you are teaching something to me therefore you are teacher or Sir for me and I am your student.