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  1. #1
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    1000w heater


    I can see how quickly the heating wire goes red hot, once powered on.I have got a heating rod of 1000W, but I'm not using it, I have taken all its heating wire and using it in another thing. I measured the resistance of the total wire in the rod and it comes around 46Ohm and I'm powering it from voltage RMS 220V.So W=V^2.R=1052Ohm quite close to 1000W and 4.78A of current would flow.Anywayz, I am using this wire to wound it on a piece of metal so that it gets hot. The metal plate is this as shown in the figure, attach with wire taken from the heater rod in first picture.



    I want to put this metal piece into this RED cloth like this



    I don't want to heat the wire very much or else this burn up red cloth envelope, this is why I want to lower the heat of 1000W heating rod wire

    Small Introduction to why I'm doing and where I'm doing.Actually there are two of them and will be attached to this machine as shown below



    If you see in the below picture, these two red plates are actually the two plates of a capacitor. Radiation passes through it and it heats the body, in this case CAT tissue will get heat up inside the cat, it's much like food getting warm up inside the Microwave oven, but the heat generated is very low.



    The machine is called as Short Wave Diathermy machine and the problem is that , the machine doesn't work at all.

    I design little part of this machine and it works perfectly![including LCD,microcontroller,buttons, relay timer,stepper motor,etc], the other part of the machine is oscillator making around 10-12Mhz frequency and causing the radiation to be passed from one capacitor plate to another and the body in between will be warm up.It creates relaxation to people when they are tired or have pain, so they use it.

    If you look inside the machine, it's totally a piece of junk





    Few ideas came to my mind for Heating RED pads with reduced heat and not by radiation, actually this machine is to be demonstrated for 2-5 mintues, once done, story ends here, but the machine is dead, so I'm doing this so that it looks like the machine is really working, but the fact is that it doesn't work at all :(



    (1)I Attached a resistor like 1.8KOhm[I choose this value,because I had this at home] of 5W in series with the heating wire, in this case the current flow should decrease and the wire shouldn't get very hot and shouldn't damage the red cloth envelope, it should give little bit heat and if a person touches on the red envelope pad, he should find it warm and the story ends here.

    Result obtain:
    ----------------
    This idea didn't work at all. Resistance got burnt up badly



    (2)The second idea came to my mind, how about if I use a light dimmer or fan dimmer for this. I have dimmer for this ordinary ceiling fan, I know it's not of 1000W.I have stairs by which I can actually climb and see what's the rating of this fan, but it's in top roof right now.If I take it out from the roof and bring back to the room, it will create noise and it's 2:57AM in night and everybody is sleeping. I will see tommorow morning.Infact I attach all these fans in home



    Question#1 from Point2:
    ==============

    If I use ceiling fan dimmer[I have opened one in the past, and the circuit was almost identical to this one]



    If I change duty cyle to low, AC cycle would get chopped and less amount of energy will be given to the heating element , but if I changed the triac to fully on, then full AC would flow and the heating element would get red hot and there would be a chance that this dimmer circuit would get damage, because probably the triac couldn't handle large amount of current. Is this thinking of mine correct? In other words if this simple regulator is connected with 1000W load or say 1500W or 2000W resistive load, this simple circuit will not get destroyed, if only AC cycle is choped largly and duty cycle is kept low and TRIAC remains off most of the time and gets on for less amount of time.This would then work. but if anybody turn the TRIAC ON all the time and let the TRIAC passes whole of the AC cycle, then this will get destroy(provided the condition that TRIAC can't handle the amount of current)

    Question#2:
    ========




    This is how I have attach the heating wire of second picture, this is a copper sheet and it's conductive and the heating wires are conductive too. What I was thinking that the current would flow in the manner as shown in the figure shown below in left, but what I came to know in the end that it was a copper sheet and the current would flow in the manner as shown below in right. What all the efforts I had done to attach the wire in this manner is gone useless, because it would only happen if the sheet was insulator and not conductor, now the attachment of heating wire is gone useless.The current wouldn't flow through all the wire, but rather it would flow throught the pure copper sheet, because current sees for the path where there's less resistance. Is this thinking of mine correct? I realized it when I made it.I hope if this thing come to my mind before.
    I know I'm using AC source, so direction doesn't matter.Current flow to and fro, but I made them to tell you people the flow of current.
    Please tell me whether my thinking is correct or not?
    If there's any other good way to do please tell me, any comments, suggestions are highly appreciated :D

    •   Alt15th December 2008, 22:52

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  2. #2
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    bta12 heatsink

    umery2k75,
    The reason your 5W resistor burned up is that it was dissipating about 25W. The total resistance was 1800 + 46 = 1846.
    .
    The current was 220/1846 = .119A.
    .
    The power dissipated in the 1800 Ohm resistor was I^2 X 1800 = 25.5 W
    Regards,
    Kral



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    1000w dimmer circuit

    Thanks Kral
    If I use resistance to lower the heat, 25W is to be dissipated across the resistor, how about this type of resistor it's of 25W



    What is the more reliable solution to it, to use a dimmer circuit to lower the heat or to use the resistor to lower it?



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    bta12-600 schematic

    In the schematic of the fan regulator, the BT136 is used for 2000 watts. Practically it is impossible to use that triac for loads above 500 watts without heatsink. With heatsink it may go up to 1Kw Max. But still not recomended.
    You can use any phase controller like the one you have mentioned ( a Fan regulator) but the triac should be replaced with a high powered one enough to with hold the consumption through it. Triac may be replaced with BTA12/600 or BTA16/600 will work well provided it is fitted with minimum of 200 gms of heatsink. Good luck.


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    •   Alt17th December 2008, 08:59

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    resistance of 1000w heater

    umery2k75,
    A resistor with a suitable power rating will work. However, the 4 Ohm resistor would dissipate 74.4 Watts. I believe that a dimmer circuit is more practical, as long as it is rated for 1000W. The dimmer circuit is more efficient, so It won't get very hot.
    Regards,
    Kral


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    bta16 heatsinks

    Thanks for the valuable suggestions,especially to pranam77
    I had put around 12 bulbs of 12V inside the red pouch and they have fitted nicely.Iam energizing the bulbs, that generate heat and that inevitably heats the pad and the jobs done here.
    I really hate for what all I had to done. I swear, I'm not gonna do !@#$%^ , that disrepects electronics for anyone.



  7. #7
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    heat current rod

    Gosh, so many things that your doing has me dismayed actually,
    you wound that wire around metal plate without realizing the implications, and your intending to power those red things almost directly from mains - ok you may use the dimmer circuit, what if it fails short, you would have flaming red things and cooked cat!
    Just holding those red things with potentially mains voltage there has me nervous.

    So can I suggest another tangent, guessing, I doubt you need more than 200watts of heat.
    why not use a transformer to drop main to say 36V,
    you could use stainless steel wire as a heater element. Couldn't do worse than using an old arc welder supply either - all in all much safer.

    You could still use a triac in the low voltage AC now to control heat, but you need a high current triac.
    Or it might be easier now to PWM a MOSFET switch.


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    heater dimmer

    Thanks Umery for pressing the "Helped me" button. It's my pleasure to have helped some one. Thanks again, Good luck


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    resistance of a 1000w heater

    @xaccto
    ok you may use the dimmer circuit, what if it fails short, you would have flaming red things and cooked cat!
    Oh yes, this thing reminds me of one more thing. Long ago, I noticed a fan dimmer didn't control the speed of the fan after operating properly for few years. It then just used to turn ON/OFF the fan, this means TRIAC must have gone SHORT.

    It's a very valuable learning.I'll always back track the design, what if this happens, what if that happens, what if this mishap happens, what if that fails, short, open,etc.
    You just made my day :D



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