# Effective voltage

Discussion in 'General Electronics Chat' started by kvi037, May 17, 2013.

1. ### kvi037 Thread Starter New Member

May 17, 2013
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0

Assumption:

- Emf = 100sin(2pi*ft) +30 sin(6pi*ft)

Whats the effective voltage?

Feb 17, 2009
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3. ### kvi037 Thread Starter New Member

May 17, 2013
17
0
Thanks for reply. Yes, that's the aswer I'm looking for

If you should do it by hand do you have to integrate from 0 to T ?

4. ### kubeek Expert

Sep 20, 2005
5,293
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You can simply do it with the two amplitudes, square them, then do the mean, then root and you get the same number as wolfram.

Side note, how does that work with a single sine wave? Mean of 10000 is still 10000, so the rms would be 100, but wolfram says 70.7 so it obviously halved the square before doing the root, why? Is it like mean of 10000 + 0? That doesn´t really make sense as it could also be 10000 + 0 + 0 which would give a different value..?

Last edited: May 17, 2013
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5. ### Jony130 AAC Fanatic!

Feb 17, 2009
4,513
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OR simply solve this

$\sqrt{\frac{1}{2\pi} \int_0^{2\pi} ( 100 Sin(2t) + 30 Sin(6t) )^2 \mathrm{d}t}$

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6. ### t_n_k AAC Fanatic!

Mar 6, 2009
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I would simply use the relationship that for a composite signal comprising N simple sinusoids each having RMS values V1, V2, ......VN then the equivalent RMS value is given by

$V_{RMS}=\sqr{(V_1^2+V_2^2+......+V_N^2)}$

The RMS value of a simple sinusoid of peak value Vp is (as we know) Vp/√2

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