# total power consumption

Discussion in 'Math' started by 1990hondacivic, Nov 8, 2013.

1. ### 1990hondacivic Thread Starter New Member

Nov 8, 2013
5
0
Hi Guys,

I am new here so take it easy on me

I am taking a electromechanical course and I am having trouble with total power consumption.

Here is the info given
R140 ohms
R250 ohms
R360 ohms
R170 ohms
E 620v

I'm not sure if I am missing something or if it just way over my head.

2. ### MikeML AAC Fanatic!

Oct 2, 2009
5,451
1,066
So is this a series circuit? Parallel? Mesh? It makes a huge difference.

3. ### 1990hondacivic Thread Starter New Member

Nov 8, 2013
5
0
Hi Mike,

I think I gave the wrong info
R1 370 ohms
R2 220 ohms
R3 480 ohms
E 450V

the circuit is series-parallel
the answers shows 388.8W
R1 and R2 are in series
R2 and R3 and in parallel
I'm not sure if that makes sense

4. ### MikeML AAC Fanatic!

Oct 2, 2009
5,451
1,066
Stare at this for a while. Do you understand how I reduced the circuit to a single resistor, and why the total power delivered by the source is the same for all four circuits?

Note the various branch currents and node voltages.

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5. ### 1990hondacivic Thread Starter New Member

Nov 8, 2013
5
0
Hi Mike,

I think that might be a little over my head to be honest.

I don't understand what that all means.

I don't understand how they get 388.8W

Thanks

6. ### MikeML AAC Fanatic!

Oct 2, 2009
5,451
1,066
Ok, Power (P in Watts or W) is the product of Voltage of the source (V in Volts) and the current delivered by the source (I in Amps).

P = V *I

To find Power, we have to figure out what current is flowing out of the source.

If there was just one resistor R (Ohms), then current (I) is V divided by R

Problem is, you have a complex circuit with three Rs, so we have to replace the three Rs with just one before we can find the power...

Chapter 1 and 2 here might help.

7. ### 1990hondacivic Thread Starter New Member

Nov 8, 2013
5
0
Hi Mike,

Thanks for the help

I understand now it all makes sense.

Now 1 last question if you would.

Power consumption is the power being used?
or is there a better way to say it?

Thanks again for all your help

Last edited: Nov 9, 2013
8. ### WBahn Moderator

Mar 31, 2012
18,093
4,918
How can R2 be in series with R1 and in parallel with R3 at the same time?

Based on the numbers given, it would appear that R1 has to be in series not with R2, but with the parallel combination of R2 and R3.

9. ### Ramussons Active Member

May 3, 2013
562
92
Would'nt a schematic be easier to discuss ?

Ramesh

10. ### WBahn Moderator

Mar 31, 2012
18,093
4,918
Always. But we don't always get what we want.

11. ### Wendy Moderator

Mar 24, 2008
20,772
2,540
Schematics are the true language of electronics IMO. Even if the OP were to take a hand drawn digital scan or picture it would cut through a lot of confusion.

How to upload an attachment.

To attach a document or picture to a post

Click "Go Advanced" at the bottom of your post,

One of several options will pop up,

Click "Manage Attachments" much further at the bottom of your post,

To upload a file from your computer click "Browse", then select the file.

Schematics should be .gif or .png format, pictures should be .jpg. .jpg formats will fuzz out schematics, and should not be used for that purpose.

---------------

If you want to display this file there is an old thread I made,

How to Display Attachments Full Size

12. ### 1990hondacivic Thread Starter New Member

Nov 8, 2013
5
0
Hi Guys,

Sorry I made a mistake.
R1 is in series
R2 and R3 are parallel

I think I understand it now

Thanks for your help

13. ### MrChips Moderator

Oct 2, 2009
12,652
3,460
I want it now!!!

14. ### 7anoter4 New Member

Nov 11, 2013
3
0
Moderator edit: I have moved this post and the next to Power Consumption Math because it is a form of hijacking. Any other posts from this OP will also be moved.

If the actual diagram would be Rtot=R1+R2||R3 =R1+R2*R3/(R2+R3)=543.46 ohm then the power consumption will be 450^2/543.46=372.62 w only.You have to supply 459.67 V in order to get 388.8 w.

Last edited by a moderator: Nov 11, 2013
15. ### MikeML AAC Fanatic!

Oct 2, 2009
5,451
1,066
The LTSpice sim and schematic I posted way back in post #4 of the original Math thread had the topology right because it did indeed dissipate 388.8W with 450V applied.