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Power dissipation in this circuit

  1. Aug 11, 2014 #1
    Hey Guys,

    Can you see what is wrong with this circuit?

    It looks fine to me but I am being told that it is incorrect and will not work. I am pretty sure I am wrong and am willing to ask for help in understanding why this wouldn't work.

    Please see attached picture for further info and any resistances that haven't been provided should be negligible to solving this.

    Thanks,
    Dest
     

    Attached Files:

  2. jcsd
  3. Aug 11, 2014 #2

    berkeman

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    Welcome to the PF.

    What is the context for this question? Is it for schoolwork? The schematic is drawn very unconventionally, and so it is difficult to understand what the connections are. For example, are the right side 2 boxes that are consuming 25A each wired in parallel or in series?
     
  4. Aug 11, 2014 #3

    sophiecentaur

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    Yes, it is unconventional and could be interpreted in several ways. How does the left hand controller get its supply? Sensors usually take very little power so what is happening there?
    The electricity behaves very literally (it's dumb stuff, in the end) and doesn't know what you want it to do unless you wire it totally correctly so your diagram needs to be done very carefully.
     
  5. Aug 12, 2014 #4
    This schematic is more theoretical for design before I build it in an automotive environment.

    I have redrawn it in a hopefully more schematic in a more appropriate way.

    To Berke- These are to be wired in series (as shown in my new attached picture).

    To Sophie- The left hand controller "1" gets its input signal from the sensor (refer to first picture which names the power wires).
    The sensor will either output high when the truck is moving fast, and low when the truck is moving slow.
    I am basically being told that the resistance of the wires is important.

    Thanks,
    Dest
     

    Attached Files:

  6. Aug 12, 2014 #5

    berkeman

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    Several problems/issues:

    1) No sensor draws 25 Amps.

    2) You don't wire power consumers in series. You wire them with parallel power connections.

    3) Is the "25A" that you show for the two controllers their maximum current draw possible, and they typically draw less?
     
  7. Aug 12, 2014 #6

    psparky

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    Pretty much nothing makes sense about this circuit.

    Electricity has a language all of its own.

    Are they wired in series and parallel? Looks strange. The red wires with the main power thru them have no ohm rating? Strange again.

    I would agree that 75 amps is pretty huge. What are you controlling......a "cruise control system"?
    Is this actually in a truck or is it some type of simulation?

    To the OP....divulge every piece of information there is so maybe this could be pieced together.

    Are you in high school, college....or just a hobbyist in your basement?

    Also, if you have 25 amps going thru .9 ohm wires.....you just dropped almost 25 volts in three parallel branches. Can't happen with a source of 24 volts. Would not make any sense. You wouldn't have any power left to power your controllers. Or is the .9 ohms suggesting the entire load....that might actually make sense.
     
    Last edited: Aug 12, 2014
  8. Aug 12, 2014 #7
    Actually I figured it out.

    First of all I want to thank everyone for their time and efforts. I apologize as well for my lack of having enough information to explain it correctly.

    I am just a hobbyist in the basement and this is mainly just a simulation for a "fake" system someone had me make up for educational purposes.

    It turns out that the numbers of the currents/voltages/resistance were irrelevant but just to know that if C1 was pulling a very high amperage (ex:450A) and the sensor was pulling very little (ex:1A) why would this setup be incorrect?

    The answer was that the sensor should have been grounded over by the negative edge of controller 1 aka to the left of the big stud point where everything is meeting up.

    This would make it so that the signal coming off the sensor would have the correct ground reference and it wouldn't read a way different value.

    Thanks for everything guys I hope I didn't make everyone's brain 'splode with my inability to explain my problem.

    Dest
     
  9. Aug 12, 2014 #8

    psparky

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    First of all, 450 amps requires a HUGE cable. Copper is expensive and heavy. Not to mention finding a battery to deliver that for more than a couple minutes would be tough. To even have an alternator deliver that much power would be expenisve and power robbing to a gas engine. 450 amps at 24 volts would rob your engine of rougly 15 HP for a controller!!! That's ridiculous. It might take 15 HP to run your air conditioner, but that is reasonable since an compressor takes lots of HP to turn.

    2nd of all, controllers and sensors are small amperage devices that typically give signals to high amperage devices....like electric motors. By signals I mean they are basically giving a low voltage, low amperage signal to turn a device on or off for example. So why on Earth would you use 450 amps to do this in your application?

    3rdly, your circuit diagram still doesn't make much sense. You need to go back and understand the basics of circuits a little better.

    Look at this link and ones similiar to it:
    http://courses.ncssm.edu/apb11o/resources/guides/G21-5.circuit_multiloop_circuits.htm

    The resistors shown are similiar to your loads above. Except, it appears you have your loads at the nodes....whereas the resistors are inbetween the nodes (typical of wiring diagrams)

    If you drawing had some internal wiring shown on the insides of the loads it might make more sense.
     
    Last edited: Aug 12, 2014
  10. Aug 12, 2014 #9

    sophiecentaur

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    I hope that person are not trying to "educate" live subjects. I can't think how you would input that design into any real simulator.
    If you want to simulate or build more circuits then you really should study how people draw them. The net is full of examples of circuit diagrams and they nearly all have very common conventions. (Steer clear of Automotive circuits in manuals; they are often just plain loony. Drawing schematics is a precise language - just as precise as Maths and moreso than regular English. Your diagram means so little that it is impossible to assess what it does, I'm afraid.
     
  11. Aug 13, 2014 #10
    I will take this as a learning lesson and will make sure to make things easier for next time.
     
  12. Aug 13, 2014 #11

    sophiecentaur

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    . . . . . . is the right attitude. Good lad.
     
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