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Circuit wiring on an appliance

  1. Jun 12, 2013 #1
    Hi there!

    I recently tried adding an on-off switch, a timer and a control dial (like a dimmer switch for the heating coil) to my unit. See diagrams attached. I also rewired a fan wire.

    Instead of the complicated circuit diagram (see first attachment), I have shown the equipment wiring in a simpler diagram (see second attached).

    I don't really know how to update and add these three things or rewire the wire to the circuit (the first attachment) i.e. where to put the switches and dimmers/which wire to rewire according to the changes etc. I am not an engineer but a design enthusiast- I wanna be an industrial designer and I was playing around with features.

    Any help on adding the few items to the first circuit accordingly will be greatly appreciated!

    Thanks so much!!

    Attached Files:

  2. jcsd
  3. Jun 13, 2013 #2


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    If you haven't had any training in basic electronics and circuits, the I highly recommend you take a class or at least buy a book or two on the subject. Attempting to rewire electronic devices can be extremely dangerous and you need to understand what and why you are doing something, not just have someone tell you how to do it.
  4. Jun 13, 2013 #3
    It should be like this,but I will suggest don't do unless you are sure what you are doing.I guess its powered by main i.e.. 120/220 VAC and that is dangerous buddy... their are many safety precautions we take before working on AC mains.

    Their are many details you will need before attempting that,most important the power rating of your device and the new circuit components you are going to add,like the heater control and timer control you showed in your pic ,does they have enough capacity (power rating given in watts) to handle the heater as heaters use a lot of power it can burn your heater control and timer control if the power capacity exceeds even may cause fire in some cases.

    Don't do that if you are not sure.

    Good Luck

    Attached Files:

    • ss.JPG
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  5. Jun 13, 2013 #4
    Hello Drakkith and debjit625

    Thank you very much for your posts. I really appreciate your comments on the matter. I am not working directly with the unit, as a future designer (I am drawing sketches of new dials, timers) and an electrician is making those changes (NOT ME). I am just trying to relay that information to him via a circuit diagram- and that is the issue: I am not trained in the sciences that much.

    I am taking a 2 hour course on: Intro to Electric Circuits I (DC) in July and Electric Circuits II (AC) in August, but I would GREATLY appreciate help on circuit design at the moment, if possible.

    debjit625: Doesn't the timer need to be in series with the heat control unit if it is to control ONLY the heating element? Your design says that it controls BOTH the fan and heat. Is that correct? How is the red wire (attachment-2nd diagram) changed/rewired.

    Would it be possible to add the features on the existing circuit I provided (1st attachment)?

    Thanks again for your power capacity recommendation. My electrician was talking about a Variac to control wattage, I think.

    Please let me know if the diagram can be shown to me so that I may show this to my electrician.

    Thank you so much,
  6. Jun 13, 2013 #5


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    That is just as bad, do you not realize. As a designer, your liability extends to the safety of third parties, be it fabricators or users.
  7. Jun 14, 2013 #6


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    You wern't very clear in the original post on what you wanted the circuit to actually do.

    PS: Your own attempt was potentially dangerous because it allowed the heater to be turned on without the fan running. That could potentially allow the unit to overheat, catch fire etc.

    If you have access to an electrician you are better off explaining to him the functionality you want to achieve and letting him draw the circuit.
  8. Jun 14, 2013 #7
    Well in your circuit diagram the (second one look at the current design) the fan is connected parallel with the heater,what will happen if you connect the fan before the timer is ,the fan will keep running whenever the unit is switched on.


    Red wires are used for phase in electric wiring,but unless we see we cant say much...

    Your circuit diagrams are not that proper so its difficult to understand...

    Variac is auto-transformer,its basically a step up and down transformer in one unit and even its not electrically isolated.They are used in voltage stabilizer.To control a heating element using a variac is a very very bad idea ,never do that what your electrician thinks is that by stepping down the voltage he will run the heater in a lower voltage and as a result it will produce less heat as the power is less,but remember every component have a working voltage range and they should be run at that range not higher or lower.To control the heater you have to control the current not the voltage,we do this by using active device name TRIAC they belong to thyristor family a semiconductor device ,in light/fan dimmers circuit they are used.

    I did that in a electronic circuit simulator program use to design/simulate electronic circuits,they are not proper symbols to represent electrical components,but still with a bit knowledge of electrical that is not that hard to understand.

    I suggest you finish your course and have some idea before proceeding,I guess your unit is a heat blower /room heater ,if you had knowledge of analog and digital electronic using power device and micro controllers you can design a much more sophisticated and a better design and cheap too.

    Good Luck
  9. Jun 14, 2013 #8
    Thanks for the updates, the unit needs the fan to be on when the switch is flicked on. Then the timer decides how much time the heater is going to run, and on what setting (that is what the heat control dial is for).

    All I wanted to know was where exactly the timer and dial/control went in the circuit.
  10. Jun 15, 2013 #9
    This is what you are talking,assuming you have verified all the components that will work with your system.

    Good luck

    Attached Files:

    • hh.jpg
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  11. Jun 16, 2013 #10
    Thanks for your input

    Thanks debjit625! (are you Bengali by any chance?)

    Your circuit is very much appreciated! Please, if you would kindly...look at the attached circuit which is the appliances (coffee roaster). Courtesy of CWatters.

    The M in this diagram is the fan in yours, and the 10 ohm resistor is the heater. The AC/L is the power power source with the switch next to it. Disregard the other components, and bridge rectifier. Given this circuit explanation, where should the timer and heat control be situated? I'm thinking between the 3ohm R and 10ohm R (in series)?! Please let me know if you have a moment.

    Thanks again for all your help!

    Attached Files:

  12. Jun 20, 2013 #11
    I was busy...with my studies
    Ya... its Roy .. Debjit Roy 007

    Well again your circuit diagram is not very clear (and that circuit might not work, unless I get the values of the components I cant be sure) ,I can't understand it properly unless you give the proper diagram with every component and their proper data parameters.What's that 3 ohms resistor, is it a heater why you are connecting two heaters and no the timer and heater control shouldn't be connected between 3 ohms and 10 ohms resistors.

    Good Luck
  13. Jun 22, 2013 #12
    Thank you for getting back to me. Bhalo laglo shune :)

    Attached is the model diagram to help clarify the appliance circuit (See first page).

    1. The Button (#6 on picture) is the switch, power cord (#7) is the AC/L power source.
    2.`Heating wires (#22) is the two resistors/heating coil.
    3. The fan/motor (#32) and the 4 diode bridge rectifier is (#33)
    5. The fuse is #25 and the thermostat is #11.

    The miscellaneous resistors and inductors are not shown with values, but I can get them to you very soon. Please kindly let me know if they are of any help. :)

    Thanks again for all your help so far!

    Attached Files:

  14. Jun 23, 2013 #13


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    See post #1 of this thread.

    As I understand it sasg28 took the circuit from an existing (so presumably working) product.
  15. Jun 23, 2013 #14
    Well I didnt have to analysis the complete circuit,to tell the circuit in the schematic is not going to work ,look at the motor's connection ,both the sides of the motor is connected to positive side of 9 V DC i.e.. across the motor you have 0V (9V - 9V = 0V) use Kirchoff's voltage law.

    May be you did some mistake with the schematic,if its a working product as CWatters.

    It seems your knowledge at this time is somehow limited on electronic/electrical ,I suggest you to study a bit more before you could successfully explain your designs to others,their are many electronic forums where you could get help from.

    And its safe to work/modify this device at some extend as it is not a high voltage device, most electronic forum will accept it.

    BTW what it is ?

    Good Luck (Amaro Bhalo laglo shune (In another language))
  16. Jun 23, 2013 #15
    Yes, I got the circuit from a working product. The circuit works just fine. Don't worry if the individual components work, just wanting to know placements of NEW components, assuming the circuit works.

    I just want to know (IN AN IDEAL SETTING) where would a heat control or timer go in the first circuit drawing I attached in my original post on this thread.

    Dhonnobad (Thanks)! :D
  17. Jun 24, 2013 #16
    Well I already answered your that question check my earlier post ,but anyway I am doing it again look at the circuit ,the 3 ohms heater is connected to directly to AC mains and the 10 ohms heater is used in a fashion to drop voltage as per the motor voltage requirement(assuming the motors current is constant) ,a very bad circuit design, if their is increase in mains voltage their will be increase in motors voltage and current ,but for protection they provided RC circuit for the motor but that will be not much help at certain conditions.

    The point is that where you could connect your heat control ,you can only connect it with the 3 ohms heater in series ,but in case of 10 ohms heater you cant as it is in series with motor if you change current in 10 ohms heater you also change current in motor i.e.. fan becomes fast and slow.If it becomes too slow the heater will heat too much and will be destroyed.

    For the timer ,commercial timer units needs proper power supply ex.. 5VDC ,9VDC ,12VDC you have to provide it from external source and and they have a relay you need to connect this relay to the controlling unit in series like switch connection.Well you can connect it to 3 ohms heater but if you connect it to 10 ohms heater it will stop the motor ,if you don't it will only control 3 ohms heater and 10 ohms will always be working.

    In short this circuit is not that flexible to be modified to something you imagined.

    Now this circuit (above) is not safe to work its not isolated from mains and its a high voltage circuit ,so don't do it...

    I guess it is some kind of hair drier.Cheap hair drier units have something like these my sister had one...

    Good Luck(Kothia thako,I am not going to hunt you believe me)
  18. Jun 24, 2013 #17
    Thank you dada, ami NY e thaki. Abong apni? :)

    So what you are saying is that both control/timer can only be connected to the 3Ohm heater and not the 10 Ohm one because it is attached to the fan motor?

    Do you think the heating and fan circuits can be disconnected to be independent circuits? i.e. can the motor draw power from the mains and not rely on the 10 Ohm heater? Does it need a transformer?

    Also, can the control/timer be then connected to the 10 Ohm heater to control it?

    If we put a control on the fan, and a timer on the heater, will it work then?

    How would you ideally change this circuit into a new one that did all of these imagined modifications?

    It is a coffee roaster/pop corn popper :p Its a cheap chinese product. I really appreciate your inputs so far!

    Bhalo theken
  19. Jun 24, 2013 #18


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    I don't see that.

    The diodes appear to form a bridge rectifier with the motor between +ve and -ve.
  20. Jun 25, 2013 #19
    @CWatters look at the pdf schematic,I was talking about that... both the input of the bridge is positive 9VDC
  21. Jun 25, 2013 #20


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    Ah OK. I think the OP explained they weren't meant to be batteries. I think this is the second thread on this subject.
  22. Jun 25, 2013 #21
    Well,we can do that powering the heater separately and using any power source (like transformer as you guessed or switching power supply if small unit is required ) to power the motor and that power source can also be used in powering the timer.I can't specifically say how to modify your circuit as their are lot of data needed ,unless I see the unit I cant say much,I cant just tell how to connect the heaters, as it have a proper working range if its not in that range then your device will not work for example if the heat becomes too low the pop corns will not pop on the other hand if the heat is too much the pop corn will burn.

    Good Luck (Ami Kolkata e thaki)
  23. Jun 25, 2013 #22
    Well I also think the pdf schematic doesn't make much sense,the first one does make sense and should work.

    If you just need to add timer to the unit you can connect it from out side just buy a commercial timer unit power it with a suitable power source,and it will have relay ,you just need to connect the relay points.

    And about adding heat control ,I think it shouldn't be done as coffee roasters/pop corn poppers needs a specific heat to work if you change that the unit may not work.
  24. Jun 25, 2013 #23
    I am in the process of deciphering the L and C values, will give you more updates very soon.

    Outside as in....where do I place it within the circuit? Do the relays just get wired in?

    The reason I need the heat control is because the corn/coffee burns too fast, and too hot. I want to control this heat by lowering it. Any ideas? My option or choice was to add heat settings, or dial (rheostat) to fluctuate or decrease heating coils heat. Or even make the fan more powerful to cool. Any thoughts on that?

    And dad, amar email thikana holo bkr.chowdhury@aol.com. Apnar ta ki msg kore pathaben jeno ektu aro kotha bolte pari?
  25. Jun 28, 2013 #24
    Hi guys, I have finally gotten the L and C values:

    The Ls are both 130mA and C1 and C2 is 0.1uF, and attached is an image of the circuit board.

    Thank you,

    Attached Files:

  26. Jun 28, 2013 #25


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    Just a thought but... If the fuse is 10A and it's a 230V appliance the heater can't be as low as 3 ohms.
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