
Home  Forums  Rules  Articles  diyAudio Store  Blogs  Gallery  Wiki  Register  Donations  FAQ  Calendar  Search  Today's Posts  Mark Forums Read  Search 
Everything Else Anything related to audio / video / electronics etc) BUT remember we have many new forums where your thread may now fit! .... Parts, Equipment & Tools, Construction Tips, Software Tools...... 

Please consider donating to help us continue to serve you.
Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving 

Thread Tools  Search this Thread 
14th October 2010, 04:52 AM  #1 
diyAudio Member
Join Date: Jul 2010

Instantaneous VoltageMath Question!
Could someone help me out with some Instantaneous Voltage calculations please.
I need to calculate the value of the resultant waveform at 45deg 120deg & 240deg that includes a third harmonic content of 20v. Vmax is 200V, third harmonic amplitude is 20v I know that to find the instantaneous voltage the calculation is: e = Vmax sin0 So e = 200 x sin 45 = 141.4V e = 200 x sin 120 = 173.2V e = 200 x sin 240 = 173.2V Do I just ADD the 20v to each result to include the third harmonic amplitude or is there more to it? Cheers 
14th October 2010, 05:25 AM  #2 
diyAudio Member
Join Date: Mar 2010

There is more to it. First, you need to know the phase relationship. The 20 V (peak?) third harmonic has to be evaluated at the instant in question. It too is sinusoidal and is defined by peak voltage times sin (3f) Plus the shift due to phase difference.

14th October 2010, 05:56 AM  #3 
diyAudio Member
Join Date: Jul 2010

bob91343,
Thanks for the reply, I think I get what your saying, I'll try to work it out & see how I go. Cheers. 
14th October 2010, 02:32 PM  #4 
diyAudio Member
Join Date: Oct 2006
Location: Charlotte, NC

Try this out.
Just an Excel 97 spreadsheet that plots out what the waveform would look like with a number of harmonics and phase shifts. 
14th October 2010, 03:30 PM  #5 
Banned
Join Date: Jan 2008

Its:
e=200*sin(45)+20*sin(45*3) e=200*sin(120)+20*sin(120*3) e=200*sin(240)+20*sin(240*3) Here's a spreadsheet showing the graph of the actual values you're interested in: 10percent_3rd_harm.zip w I've taken the phase relationship as 0 degrees. Last edited by wakibaki; 14th October 2010 at 03:32 PM. 
14th October 2010, 09:27 PM  #6 
diyAudio Member
Join Date: Jul 2010

Thanks for the replies guy's & also the Excel spreadsheets,
I see how this is calculated, much appreciated. If I could ask one more question. How does the phase relationship factor into the equation, could you possibly give me a quick example, basically for future reference. Thanks Guy's Cheers 
14th October 2010, 09:54 PM  #7 
diyAudio Member
Join Date: Mar 2010

The phase relationship causes the voltages to add in different ways. As the waveform changes you will get different results, although the rms will be unchanged.
Just pick a phase and plot it with graph paper, adding the voltages at each instant of time. The wave could be flattened or peaked but will be symmetrical with only odd harmonics. 
14th October 2010, 10:20 PM  #8 
Banned
Join Date: Jan 2008

OK, suppose the 3rd. harmonic was 60 degrees lagging the fundamental then the equations would become:
e=200*sin(45)+20*sin(60+(45*3)) e=200*sin(120)+20*sin(60+(120*3)) e=200*sin(240)+20*sin(60+(240*3)) w 
14th October 2010, 10:33 PM  #9 
diyAudio Member
Join Date: Jul 2010

Thanks very much, I understand.
The posts have been very useful. Thanks again Cheers 
Thread Tools  Search this Thread 


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Integrator "instantaneous" reset  RiskCord  Parts  1  26th May 2008 05:42 PM 
Math to calc optimal voltage of tube dac to match amp input sensitivity?  riotubes  Tubes / Valves  7  9th November 2006 11:08 PM 
LM4780 instantaneous peak output power capability  percy  Chip Amps  0  18th October 2004 03:15 PM 
2 Question regarding Math Cad Sheets  tda  MultiWay  8  6th January 2004 12:13 AM 
radiation pattern math question  blu_line  MultiWay  6  31st October 2002 05:04 PM 
New To Site?  Need Help? 