Author Topic: thevinan's theorum and solving for multiple power supplies.  (Read 1707 times)

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Offline blackbeardTopic starter

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thevinan's theorum and solving for multiple power supplies.
« on: December 06, 2009, 07:46:35 PM »
[img=http://img19.imageshack.us/img19/7639/thevandmc.th.png]

so i can't seem to figure out thevinin's theorum. online resources don't seem to help and i was wondering if you could tell me the process for solving a circuit like the lower one in the picture. also i don't know how to solve for a circuit with multiple voltage sources such as the one in the picture. i've tried the online sites but i don't understand what they're trying to say. can someone explain in laymen's terms?
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Offline Soeren

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Re: thevinan's theorum and solving for multiple power supplies.
« Reply #1 on: December 07, 2009, 04:26:23 AM »
Hi,

so i can't seem to figure out thevinin's theorum. online resources don't seem to help and i was wondering if you could tell me the process for solving a circuit like the lower one in the picture.
Seriously? You don't take the time to at least number the resistances, why would anyone else?
How do you think a formula with 4 (or 5?)resistances all named "R" would help?
Help yourself - present your questions in a way that they can be read and answered without extra effort to redraw your schematics.
And if the rightmost resistance is ment as the total resistance, don't draw an extra resistance, that just obfuscates things.
And while we're at it, it's Thévenins theorem (named after its inventor Léon Charles Thévenin). When theorems, formulas etc. is named after a person, it's allways written with a capital first letter.


also i don't know how to solve for a circuit with multiple voltage sources such as the one in the picture. i've tried the online sites but i don't understand what they're trying to say. can someone explain in laymen's terms?
Well, laymen has no use for, neither should be expected to understand Thévenins theorem and it is not possible to do it in a non technical way, but I'm sure you'd be able to understand a technical explanation, as soon as you get around to actually name your resistances AND define your load(s) (which is quite important, as it is needed to be able to solve anything).

So, back to the drawing board ;D
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline blackbeardTopic starter

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Re: thevinan's theorum and solving for multiple power supplies.
« Reply #2 on: December 07, 2009, 09:01:26 AM »
sorry about that. i was more wondering a brief description of the process rather then an example since that would take long for the person doing it. i'll edit it and repost it


EDIT: posted

[img=http://img709.imageshack.us/img709/7639/thevandmc.th.png]
« Last Edit: December 07, 2009, 09:08:39 AM by blackbeard »
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Offline Soeren

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Re: thevinan's theorum and solving for multiple power supplies.
« Reply #3 on: December 07, 2009, 04:24:32 PM »
Hi,

Something's wrong with the link, I only get:
"503 Service Unavailable
No server is available to handle this request."
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline blackbeardTopic starter

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Re: thevinan's theorum and solving for multiple power supplies.
« Reply #4 on: December 07, 2009, 07:27:08 PM »
might have just been down. try this one
http://img709.imageshack.us/i/thevandmc.png/
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Offline Soeren

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Re: thevinan's theorum and solving for multiple power supplies.
« Reply #5 on: December 07, 2009, 09:44:22 PM »
Hi,

You don't care much for this do you?
2 of R1 in the lower circuit and 2 of R3 in the upper circuit.

Anyways... For the lower circuit:
R3 and R4 is an easy parallel combination yielding 50k.
Kirschoff tells us that the current in a loop won't change if you rearrange it.
So, move the lower R1 up in series with the one on the positive terminal (giving 50k) and now you have a simple voltage divider of 50k each side.
Do you know how to continue from that?

For the upper circuit, you still haven't defined where you assume the load to be connected (and hence where to calculate the Thévenin equivalent to).
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline blackbeardTopic starter

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Re: thevinan's theorum and solving for multiple power supplies.
« Reply #6 on: December 08, 2009, 08:10:23 AM »
doh >.< i'm sorry. i don't know how that slipped out. this is all for theory but i need to solve circuits (albeit much more complex) with Thevinin's theorem which have multiple current sources but i'd like to know how to solve multiple current sources without thevinin's theorem to start so i can get a grasp of it. i think i have a grasp of Thevinin's theorum but multiple current sources still confuses me. anyways i fixed it so hopefully third times the charm

http://img13.imageshack.us/img13/7639/thevandmc.png
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Offline definitionofis

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Re: thevinan's theorum and solving for multiple power supplies.
« Reply #7 on: December 08, 2009, 09:28:23 AM »
 ::)
« Last Edit: December 08, 2009, 10:27:33 AM by definitionofis »

Offline Soeren

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Re: thevinan's theorum and solving for multiple power supplies.
« Reply #8 on: December 08, 2009, 11:29:48 AM »
Hi,

[...] but multiple current sources still confuses me.
Don't wanna be a nitpick, but it seems you're mixing voltage sources or current sources. Which are you thinking of?

Are you familiar with Nortons theorems and Kirschoffs Laws etc.?
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline guncha

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Re: thevinan's theorum and solving for multiple power supplies.
« Reply #9 on: December 08, 2009, 11:54:18 AM »
Referring to the last schematic you posted:

1. You need to use both Kirschoffs Laws. If you don't understand them completely yet, start with that. Then it's just writing two equations for each current loop, solving them and you are done.

2. You don't need any fancy theorems to solve second circuit. All it takes is adding up R3 + R4 + Rload -> getting total resistance -> current flowing -> current flowing trough Rload using proportions.

Though.. now I'm not really sure what do you mean by "solving" them.

Offline blackbeardTopic starter

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Re: thevinan's theorum and solving for multiple power supplies.
« Reply #10 on: December 08, 2009, 04:50:18 PM »
oh ya i can solve the second circuit without Thevinin's theorem but i was just using it as an example. and yes meant voltage sources. thanks yalls.
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Offline Afroman

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Re: thevinan's theorum and solving for multiple power supplies.
« Reply #11 on: December 09, 2009, 12:15:02 AM »
To solve circuits with multiple voltage/current sources, use the technique of superposition

e.g.
http://www.circuit-magic.com/super_position.htm
http://holbert.faculty.asu.edu/ece201/recipes.html

"Procedure:

   1. For each independent voltage and current source (repeat the following):
         1. Replace the other independent voltage sources with a short circuit (i.e., v = 0).
         2. Replace the other independent current sources with an open circuit (i.e., i = 0).
                Note: Dependent sources are not changed!
         3. Calculate the contribution of this particular voltage or current source to the desired output parameter.
   2. Algebraically sum the individual contributions (current and/or voltage) from each independent source. "

So with your problem, replace V2 with a short circuit, and solve all the voltages and currents using only V1 in the circuit. Write everything down. Next, replace V1 with a short circuit, and solve all the voltages and currents using only V2 in the circuit. Finally, add the voltages together and currents together to get the final answer. For example, you will end up finding the current going through R4 twice by using the two sources separately, so just add both those currents together to find the overall current going through R4.

Offline blackbeardTopic starter

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Re: thevinan's theorum and solving for multiple power supplies.
« Reply #12 on: December 09, 2009, 09:29:05 AM »
awesome thanks allot! that clears things up entirely.

p.s. just curious but are you this afroman? http://www.afrotechmods.com/
"sure, you can test your combat robot on kittens... But all your going to do is make kitten juice"

First step: Build androids with AI
Next step: Give them vaginas

 


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