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B Step Up Transformer: Current AND Voltage Increased????

  1. May 14, 2016 #1
    Please help! I have recently completed an experiment on transformers, using a step up transformer. I am aware of all the theory that shows that in a step up transformer, the induced voltage should increase and the induced current should decrease. However, in my experiment, my hypothesis is not being supported because in every test that has been completed, the induced voltage goes up AND the induced current goes up. The resistance, number of primary coils and primary voltage has all been kept constant- the only thing that has changed is the number of secondary coils. Please help me as to why my data does not match the theory!
     
  2. jcsd
  3. May 14, 2016 #2
    What was your load??
     
  4. May 14, 2016 #3
    How do I calculate the load? The only values I have are the voltages and currents over time, and the time. It was recorded through Logger Pro if that's any help. I think I need the load line to line voltage and the maximum load phase current to calculate the load but I'm not exactly sure if I have those values...
     
  5. May 14, 2016 #4

    davenn

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    that isn't worded correctly, which leads to you making incorrect assumptions about your results

    again this is incorrect

    What you should be realising that the "rule/law" says that with a step up transformer the AVAILABLE/MAXIMUM current that transformer can supply decreases

    since you have given no figures for your claims, you need to redo your experiment and actually measure the primary current and the secondary current
    In a step up transformer, the secondary current will always be less than the primary current for a given load value


    Somehow I doubt that statement
    what is the load ? a resistor ? a lamp ? something else. we need to know if the load is inductive or resistive ?

    so far your experiment is full of holes ... do the proper measurements and post them in this thread and tell us what the load is


    Dave
     
  6. May 14, 2016 #5

    Dale

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    Experimental error. Please provide a table with the number of secondary coils, the secondary voltage, the secondary current, the primary voltage, and the primary current. Please also describe how each was measured and include a circuit diagram showing the configuration and label all relevant points where leads were placed.
     
  7. May 14, 2016 #6
    Is it possible a real lossy transformer could do this or a short in the coils?
     
  8. May 14, 2016 #7

    russ_watters

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    This might just be another of the common misunderstanding about transformers(and a poor description of the experiment): if you add a step up transformer to a simple circuit like a resistor, both the voltage and current to the load do indeed both go up.
     
  9. May 14, 2016 #8

    CWatters

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    +1

    It's best not to think of a transformer as changing the current. In the majority of cases it is the load that determine the current on both sides of the transformer.

    When analysing a transformer circuit it's best to work from the source to the load to determine the voltages. Then work from the load back to the source to determine the currents.

    1) Consider a 1V AC source and a 1Ohm load resistor...
    With no transformer the current in the resistor is given by I = V/R = 1/1 = 1A. The power is I*V = 1*1 = 1W

    2) Now insert a 1:2 step up transformer that doubles the voltage....

    Circuit voltages...Starting at the source you have 1V AC then the transformer steps that up to 2V. There is now 2V on the load.

    Circuit currents...Starting with the load.. The current in the load resistor is now V/R = 2/1 = 2A. That's also the current in the secondary. The current in the primary is double that in the secondary so the primary current is 2*2 = 4A.

    The power in the load is now 2*2 = 4W. eg four times what I was without a transformer so the situation has totally changed.

    With the transformer the primary current is 4A and the secondary current 2A. That's what they mean by the transformer reducing the current. They do not mean its reduced compared to the situation without a transformer.
     
  10. May 14, 2016 #9

    berkeman

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    This thread is closed. Please repost in the Homework Help forums, where all schoolwork goes. And please fill out the Homework Help Template you are provided there. Thank you.
     
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