Powering a heater coil

Discussion in 'The Projects Forum' started by Lucyfur1, Jul 29, 2015.

  1. Lucyfur1

    Thread Starter New Member

    Jul 16, 2015
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    Hello everyone!

    For my project, I pulled a simple resistive heating element out of an AC unit. It draws 5kW, and since the amperage it uses is ~20 amps, I'm very positive it uses 208 volts, single phase.

    I need to power this heating element, but I've never done anything like this before (I do have experience with pulling apart treadmills for the motor and have a electrical background). My application is to warm air that is blowing over it in a ducting system.

    Like I said, I have never worked with a heating element before. The only leads it has are two brown leads (?). The wiring diagram only states that one brown wire goes to "heater 1" and the other goes to "heater 2" - which makes me more confused because there is only one coil. They are not separated in any way.

    Thanks for your time, if you have seen this before please give me some insight! Thanks!
     
  2. ISB123

    Well-Known Member

    May 21, 2014
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    Doesn't matter how you connect it since its using AC make sure that circuit breaker is 25A-30A otherwise its going to trip,use a fuse in series with one of the wires pref. 25A.
     
  3. Lucyfur1

    Thread Starter New Member

    Jul 16, 2015
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    I think the breaker is only rated for 15 or 20 amps. Would a fuse protect the breaker from tripping? Also I want to be careful I don't damage the wires in the wall. I understand that if I use a breaker that is rated higher than what the wires in the wall can handle, it will cause them to melt and consequently a lot of damage.

    Thanks for your help.
     
  4. #12

    Expert

    Nov 30, 2010
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    If the wires in your walls melt, you have the wrong circuit breaker installed in the mains panel and you are in desperate need of an electrician. DO NOT change the breaker in the mains panel in order to overload the wires. Instead, choose a circuit that is already capable of the power you require. If you don't have such a circuit, read the first and second sentences again.
     
    Last edited: Jul 29, 2015
  5. ISB123

    Well-Known Member

    May 21, 2014
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    It wont work,breaker can only supply 20A before it trips.If heater is pulling 20A breaker detects it as circuit fault.You need 25A breaker,fuse and 10 gauge wire(2.5mm).
    Fuse acts like a normal wire until it reaches its melting point which breaks the circuit.Use the fuse as secondary safety option along side the breaker.
     
  6. #12

    Expert

    Nov 30, 2010
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    Who told you the circuit breaker is rated for 20 amps?
     
  7. ISB123

    Well-Known Member

    May 21, 2014
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    I dont understand what you mean?
    He said that his house only has 15-20A breakers.So im telling him that he needs 25-30A breaker with 2.5mm wire if he wants the circuit to work.
     
  8. #12

    Expert

    Nov 30, 2010
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    Oh, there it is. Post #3.
    Unfortunately, TS seems to think you told him to go to the breaker box and change the circuit breaker to a larger size. Please be clear about your intent.
     
  9. strantor

    AAC Fanatic!

    Oct 3, 2010
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    A lot of times resistive elements will have taps with connecting bars. The bars can be rearranged to put sections in series or parallel, for different voltages. if you post a picture we can investigate.

    Also I would expect a 208V heater to be 3phase.
     
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  10. #12

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    @strantor
    I expect you're part right and part wrong. A 5KW heater at 20 amps calculates to 250 volts, so I think the TS is mistaken. I have never seen a heater in an air conditioner with adjustment taps. 5KW is a standard size. Some come with the bolts on the ends already spot welded to the nichrome, and that is about as convenient as they get.
     
  11. strantor

    AAC Fanatic!

    Oct 3, 2010
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    There I go again, reading what i want to see instead of what OP wrote. He did say "out of an A/C unit," and i was replying under the assumption it was an immersion heater.
     
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  12. Lucyfur1

    Thread Starter New Member

    Jul 16, 2015
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    Hey all,

    Thanks for your input. Okay so first off I'm in a commercial building so I may be able to call an electrician to modify my current system to one that can handle 30 amps.

    The AC Unit consumes 1 phase power, I checked the technical info. on the unit's panel.

    So at this point, it looks like I can't power the heater with the type of breaker I have. Is there a way around this? I'm assuming that the heater can handle up to 5kW but does it need that much to produce heat?

    I can't get a photo right now, but here's what it looks like (see attachment). It's shape is a little different and it only has 1 pair of input "tabs" (for lack of a better word) but it's essentially the same type of heater. By tabs I mean they are these small cylindrical parts connected to the end of the coil, where the leads from the control board are attached.

    Thanks again for all your help.
     
  13. Lucyfur1

    Thread Starter New Member

    Jul 16, 2015
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    By this I mean I wonder if I can supply 120V to it from a regular outlet or supply DC power....but that would require the same amount of voltage I guess.

    Another thing that confuses me is the amount of power the heater draws? Wouldn't it just consume up to 208V/15Amps and stop at that point? It's only a simple resistive coil with two leads.
     
  14. strantor

    AAC Fanatic!

    Oct 3, 2010
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    Can you tell us what it's actually rated (as in, what it says on the label, if there is one)?
    Do you have a multimeter to measure the resistance of the coil?
    Because your numbers aren't consistent.

    5,000W/208V = 24A, you say ~20A (to me, that could mean anything from 15A to 25A)
    If it is indeed rated 5KW, and rated 208V, then it should have a resistance of:
    208V/24A = 8.67 ohms
    If you were to power it with 120V instead of 208V, it would draw:
    120V/8.67ohms = 13.84A
    And could therefore be able to run on an existing 120V/15A circuit, but it would result in a:
    120V*13.84 = 1.66kW heater instead of a 5kW heater

    If you can post the actual resistance of the coil, and/or the rated specs of the heater, more realistic feedback can be given.
     
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  15. Reloadron

    Active Member

    Jan 15, 2015
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    The image you posted discounting the dual elements would be typical of those found in for example home clothes dryers or air conditioning units that have a heater function. The 208 volts leads me to believe industrial only because typical US residence would be 120 or 240 volts. Regardless it works as strantor pointed out, if you apply 120 volts it will not draw its rated current and get as hot as it normally would. You can try 120 volts, it won't hurt it.

    There is a caveat to all of this. Elements like this are designed for a given airflow over the element. Without an airflow the element will likely glow a cherry red and self destruct. Systems using elements like this normally have a thermal switch sensor in close proximity to the element to prevent the element burning up. The idea being when excessive (high) temperature is detected the power is removed. Home use residential clothes dryers also typically use elements rated around 4.0 KW to 6.0 KW give or take.

    I would power the element using 120 volts and see what you get but watch the element closely as without any forced airflow even at 1/2 its rated voltage it may want to self destruct. Just something to keep in mind. Remember unless you have forced airflow over the element you are not removing the generated heat. I am not saying the sky will fall and you will grow warts, I am saying keep an eye on the thing. :)

    Ron
     
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  16. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    These posts make me angry...

    You are in a commercial building and do NOT have the knowledge nor the authority to do anything.
    Anything you do is going to be against code. If the heating unit is not listed for use in that application and hundreds of other variables..blah blah blah
    Stop immediately.. before you hurt someone/cause a fire/kill someone/kill yourself..
    Leave it to the professionals.
    You aren't qualified to be doing any work. But will absolutely be held liable for any damage you cause.

    This post should be locked IMO and the OP should call an electrician/hvac specialist,etc...
    You are out of your league here..
     
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  17. #12

    Expert

    Nov 30, 2010
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    mcgyvr has a good point. Information provided to this point leaves plenty of room to hope that nobody gets hurt when the heating coil melts and the project is abandoned. The coordination of heater watts and air flow is paramount. So far, we are still working with a failure in Step 1: Read the label!
     
  18. Lucyfur1

    Thread Starter New Member

    Jul 16, 2015
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    Okay mcgyvr, before you explode from anger you should know that I do have the authority to request electrical modifications to the workspace. Obviously I'm not going to wire this heater up while it's sitting next to my cubicle, OR am I going to start messing with my breaker. "Leave it to the professionals" = call an electrician, which I planned as an option.

    If I didn't understand the risks and danger behind this, I wouldn't have posted this thread. But I do, so that's why I'm here doing my research like a responsible person does.



    Thank you for your input Ron! If I do this, I will definitely do it in a controlled environment.
     
  19. tcmtech

    Well-Known Member

    Nov 4, 2013
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    Unfortunately if this is in a commercial environment you would be money and time ahead to simply buy a common portable electric heater for yourself.

    Now that's said if you are going to play with this at home you can basically do whatever you want within reason being to me that's how learning new things works.
    As for your own safety I see that to be of little concern to me and should be the same for everyone else. It's not like you getting yourself hurt while learning is any different than how most of us learned our harder lessons about electricity and heaters and whatnot. :D
     
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  20. Lucyfur1

    Thread Starter New Member

    Jul 16, 2015
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    Okay so my colleague just told me he ran the heater (when it was still in the AC Unit, before we dismantled anything) and nothing tripped. We've decided we are going to run it off of the 120V outlet coming from the wall or just find another heater.

    Thanks everyone for your help and safety concerns. Happy Thursday! :);):D
     
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