resistors and poteniometers

Discussion in 'General Electronics Chat' started by sherlock ohms, Dec 24, 2013.

  1. sherlock ohms

    Thread Starter New Member

    Dec 24, 2013
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    New member with no formal electrical training, but I have been studying circuits, electricity, and appliance repair electrical on my own and love diagnosis and troubleshooting but most of all understanding (or trying to) the electrical fundamentals of why a circuit works the way it does.

    First of many questions....
    *Does a resistor in an AC circuit reduce the Voltage or reduce the amperage?
    An electric dryer's timer circuit on one setting switches from a straight 110v line feed to neutral to the 220v (110v, 110v) circuit normally used for the heater. This time though one leg of the current passes through a resistor. Does this effectively make the 220 circuit a 110v circuit?

    *A pellet stove uses a potentiometer wired to what seems to be a time delay relay/timer switch. Would anyone know what is going on inside that switch? It has two incoming voltage fees, a neutral, and two wires from the potentiometer, but I cannot tell how all these wires are working in conjunction.

    thanks in advance to any and all who might comment, s o
     
  2. BillB3857

    Senior Member

    Feb 28, 2009
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    Question 1.... With a name like Sherlock OHMS, that should be simple. Google Ohm's law and you should be able to go from there.

    Question 2.... Two power wires in, a neutral and two pot wires and nothing out?? Very strange, indeed. Are you sure one of the two power wires in isn't a timed power out, maybe to run a pellet drop motor or draft fan?
     
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  3. crutschow

    Expert

    Mar 14, 2008
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    The resistor can drop either voltage or current or both depending upon it's connection in the circuit. From Ohm's law the voltage across a resistor equals the current times resistance (V = I*R). Rearranging the terms, the current through a resistor also equals the the voltage divided by the resistance ( I = V/R).

    So the resistor in series with the electric dryer element will reduce the voltage across the element and consequently the current through the element. How much it reduces depends upon the relative resistance value of the resistor and the element. If they are equal, then the element voltage and current will be reduced by 1/2.

    The potentiometer likely adjusts the amount of the time delay in the switch. I can't say exactly how it does that without knowing what the internal circuit of the relay/timer switch looks like. Typically it would adjust the charging current to a capacitor, which determines the time delay (as per the RC time-constant).
     
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  4. inwo

    Well-Known Member

    Nov 7, 2013
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    Nothing to do with answering your question. The answers so far are valid.

    It is unlikely that a resistor is in series with the main heating element.
    If you could post a schematic or link, someone would give a more relevant answer.

    A resistor would only be used in very low power circuits as it is the nature of resistance to dissipate power/heat. Not normally a good thing to waste a lot of power.

    I'm thinking it's in a control circuit. Maybe to a heat anticipator or semi-mechanical heat activated control.
     
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  5. inwo

    Well-Known Member

    Nov 7, 2013
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    As far as the timer goes;

    A little unusual for mains (ac) power at the pot.

    Most likely only a common connection to mains power.
    Although I can think of ways to vary time period of a timer, with varied ac from a pot, most likely it would use low level dc slowly charging a capacitor to delay an output.

    A water analogy would be a valve filling a bucket. When the bucket is, say, 2/3's full it hits a switch, and another valve emptying the bucket.
     
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  6. sherlock ohms

    Thread Starter New Member

    Dec 24, 2013
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    I appreciate your helpful reply. I do know of Ohm's Law but I wasn't sure I understood it. If I have 120 v and a resistance of say 10, my amps are 12. But if both voltage and amps are affected by a reistor, and this is what I wasn't sure of, I could get an equally true equation of 100v (reduced), same R of 10, and 10 amps (reduced).
    I may well be incorrect on the double voltage feed, since I do not clearly understand the wiring diagram. Not counting the two connectors to and from the pot, there are three connectors at the bottom of the relay. The Left (neutral) and Right are labeled "input" and the Middle and Right are labeled "load."
     
    Last edited: Dec 24, 2013
  7. sherlock ohms

    Thread Starter New Member

    Dec 24, 2013
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    Thank you for you helpful reply. It seems the resistor in the 220 v circuit allows the timer to run as if it were still on 110v feed. I think this is kind of neat, to power a timer rated for 110 volts on what appears to be a 220v circuit, but due to the resistor, is stepped down to an actual 110v. Have I got it??
     
  8. MaxHeadRoom

    Expert

    Jul 18, 2013
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    That may be so, but it seems unlikely to me that a manufacturer would not use correct rated item and instead do a make a shift solutions such as add a dropping resistor to obtain 120v?
    A photo of any of the items may clear it up.
    Older appliances used a synchronous clock motor for timers before the later electronic versions.
    Max.
     
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  9. sherlock ohms

    Thread Starter New Member

    Dec 24, 2013
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    I have only a wiring diagram.
    In Regular mode, the timer advances steadily on a 110v to neutral circuit.
    In Auto mode, when the heat cuts, the timer is still fed by the same one leg of the 110v circuit, but the path to neutral is now diverted to the other 110v leg and a resistor.
     
  10. MaxHeadRoom

    Expert

    Jul 18, 2013
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    ??
    What about posting the wiring diagram?
    Max.
     
  11. inwo

    Well-Known Member

    Nov 7, 2013
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    If you're not able to post diagram. How about a model#?

    It might clear up some misconceptions.

    Rare that a resistor alone is used to lower voltage a fixed amount.
    Due to ohms law.
    The voltage drop isn't set by the resistor alone. Voltage drop also changes with current. Which changes according to how hard the timer is working.

    With a water analogy;
    Picture a main water shut off valve. Used to reduce pressure, when there is too much water pressure for appliances in the home.

    If using a fixed amount of water (current) in the home, the valve (resistor) could be easily adjusted to the pressure (voltage)needed.

    Now picture opening all the taps. Then closing the taps.;)
     
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  12. sherlock ohms

    Thread Starter New Member

    Dec 24, 2013
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    [​IMG]I think this is what happens: When the thermostat heater opens the operating therm, the 220v heater circuit is interrupted now allowing current from the timer to flow from TM to OR when it couldn't before as the timer presented more R than the heater. But now it seems the timer is being energized by a 220v circuit but that's when I think that resistor comes into play, but I'm an not knowledgeable enough yet to understand how.
     
  13. inwo

    Well-Known Member

    Nov 7, 2013
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    Afraid my old eyes aren't good enough.

    Is it a gas dryer?
    What heaters then? Ignition?
    Only see 120vac. Can't make out a 240vac line!

    Post the model number. I'll look for a manual online.
     
  14. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Can you post it as a PDF to make it clearer?
    Max.
     
  15. sherlock ohms

    Thread Starter New Member

    Dec 24, 2013
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    Thank you very much for your willingness to help me out. The model is 110.96573220 Sears, and it is electric. I'm am not so computer savvy so my son cut and copied this diagram. I know of no other format to send it, sorry.
     
  16. inwo

    Well-Known Member

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    The diagram posted say's "gas" on the bottom.:confused:

    Is this one close enough to get questions answered?
     
  17. MaxHeadRoom

    Expert

    Jul 18, 2013
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    On that one the only connection to 240v is the heater itself.
    Max.
     
  18. inwo

    Well-Known Member

    Nov 7, 2013
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    I couldn't find the correct one for op's model.
    This one is typical, and shows the resistors biasing the thermostat.
     
  19. sherlock ohms

    Thread Starter New Member

    Dec 24, 2013
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    My face is very red. That diagram looks simlar to the correct one but it is not the correct one. I will seek help in posting the right one.
     
  20. sherlock ohms

    Thread Starter New Member

    Dec 24, 2013
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    http://www.freeinfosociety.com/electronics/schemview.php?id=1564

    Correct schematic for electric dryer is here, I hope.
    Original question: In the Automatic mode, the timer switch closes at TM to OR, but does not advance steadily even though a complete circuit exists. My newbie knowlege leads me to believe that the current originating at BK bypasses the timer due to the Resistor and insteads flows through the Heater element which offers less R than the timer motor.
    However, when the operating therm opens, breaking the Heater circuit, the current which once was bypassing the Timer now flows through it, since that is the only route available.
    Now the queston....it seems as if the Timer is now running on both legs of the 220v circuit, 120v in, 120v plus resistor out, using one of the legs essentially as a Neutral. What is the role and purpose of the resistor here? Is it dropping the 220v circuit to a 110v circuit so as not to fry the Timer?

    Thanks again for your continued patience and willingness to teach. scott aka so
     
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