Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Ammeter to help the circuit work

  1. Oct 29, 2007 #1
    Ammeter to help the circuit work!!!

    I have connected one IC circuit which is taking from a remote control car. Then I connect it to the a power supply which is 9V. It doesn't work in the beginning. But I don't know why it works after I connect an ammeter in parallel to the resistor which in in series to the motor. The circuit diagram is attached. I have tried to use a variable resistor to instead of the 4k7 ohm resistor and remove the ammeter. But the circuit doesn't work. Do I need to use a capacitor to stablize the current flow into the motor. Or I need to add another amplifier to increase the current input into the motor. But I think it is quite dangerrous to add a amplifier directly in series with the motor since it may burst. Also, do I need to add an inductor to store the energy. Thank you for any help for that.

    Attached Files:

  2. jcsd
  3. Oct 29, 2007 #2


    User Avatar
    Science Advisor

    Where's the motor in your diagram?

    Why do you have an ammeter connected in parallel instead of series?

    What is the IC chip supposed to be doing?
  4. Oct 29, 2007 #3


    User Avatar
    Science Advisor
    Homework Helper

    An ammeter has close to zero ohms resistance.
    If it works this way without burning anything out then you either do not need the 4k resistor or it should be a very much smaller value.
  5. Oct 30, 2007 #4
    The motor is connected in series of the switch. I have tried 500 ohms resistor insteads of the 4k7 ohm resistor. However, the resistor starts to heat up to an unacceptable level in a short time. Hence, I change it to 1k ohms. This doesn't move again in this case. I don't try less than 100 ohms since I think it will burn the IC circuit. I have burnt one IC circuit when I connect it directly without any resistor in the circuit to reduce the current.

    The IC chip is a complicated circuit which I don't know how to draw it. The chip model is SDRX2BD and there is code of B 60200397. It has 18 resistors, 9 inductors and 11 capacitors in the IC circuit. If it is necessary, I can draw it in the spice software. But I really don't how to draw it in the photoshop. Thanks for any help for the circuit. I really appreciate the reply of the message.
  6. Oct 30, 2007 #5


    User Avatar
    Science Advisor

    Before or after the IC chip?

    Can you draw the circuit as it is actually connected? That makes troubleshooting a lot easier!
  7. Oct 30, 2007 #6


    User Avatar
    Science Advisor
    Homework Helper

    How much current can the IC source?
    How much current does the motor draw direct with no IC?
    What are the heatsink requirements for the IC?
    Are you using a damper diode on the motor?
  8. Nov 3, 2007 #7
    i should assume that the current is bypassing the resistor and going straight through the ammeter and taking the path of least resistance (as electricity does).
    the idea of a resistor is tho provide resistance(duh) to lower your current so if you have a large current and you add any resistor you should expect energy loss in the form of heat, more resistance, more heat. that is afterall how they work, converting electrical energy to heat energy(at least thats how the old wire resistors worked). the resistor in parallel to your ammeter adds more capacitance to your "wire" and has the opposite effect of a resistor. why this already does not cause your circuit to overheat, if it is from a 500ohm resistor, i do not know...
    if you cant figure out what to do i suggest you make that ammeter a permanent fixture of your circuit and (possibly) remove the resistor with it in place. the ammeter itself is a resistor,just not anywhere near as strong.
  9. Nov 3, 2007 #8
    Please do not add confusion to this discussion. This makes no sense.
    Last edited: Nov 3, 2007
  10. Nov 4, 2007 #9
    its like placing 2 resistors in parallel, where Rt=1/R1+1/R2. the ammeter also acts as a resistor in this case(just not a very strong one). decreasing your total resistance means you are increasing the capacitance of the "wire". electricity flows easier through wire with less resistance and higher capacitance as it allows for a higher current.

    i am refering to the parallel resistor and ammeter as the wire. i use the term wire because it is easy to understand how a thin wire has more resistance and a thick wire has less resistance.
  11. Nov 4, 2007 #10
    It has nothing to do with capacitance. I think you mean current carrying capacity/ability, or what is referred to as ampacity.
  12. Nov 4, 2007 #11
    well yes, thats what i mean.... i dont mean capacitance like farads

    Lmkjason, just replace thae word capacitance with the word ampacitance in what i said and perhaps it will help you find a soloution...
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Ammeter to help the circuit work
  1. How does ammeter work? (Replies: 29)