personal portable heaters

Discussion in 'General Electronics Chat' started by superway, May 2, 2011.

  1. superway

    Thread Starter Active Member

    Oct 19, 2009
    128
    0
    Hello,

    I have 4 personal heaters (each is 1500W, 12.5A, 120vac). I want to use as the load and connect in parallel and series for 120vac and 240vac output of my product. Enclosed is my drawing, is it ok for 240vac to the heaters in series?

    Thanks

    ken
     
  2. #12

    Expert

    Nov 30, 2010
    16,313
    6,817
    Just on the basis of, "will the heaters work", yes. The problems that must be considered include getting your power phases correct. With all those switches, there is plenty of room for error which would blow a fuse. What? You didn't put any fuses in?

    Then there is the original design of the personal heaters which did not include switches and insulation rated for the higher voltage. All bets are off as far as safety is concerned. Officially speaking, I must suggest adding GFCI protection and some fuses. I expect you won't do that, so be really careful. The smoke that gets out might be you!
     
  3. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    7,392
    1,606
    Looks like for 120V you can turn on each load in turn to get 1 load of 1*I to 4*I. That looks fine, using the product as intended. For 240V looks like to put 2 heaters in series and can switch a load of 1*I or 2*I.

    I don't see any major issues. As mentioned, the switches already inside the heaters will not have the 240V rating, so don't use them, just leave them closed; they ARE rated for the current, and leaving them closed avoids any potential voltage issues (no pun intended) (the voltage rating of a switch only comes into play when the switch is open, otherwise the voltage across a switch is zero).

    I find all those switches scary; close the wrong ones and you get the heaters in parallel (not series) at 240 V.

    Personally I would make a 120V load and a 240V load using the plugs on the heaters to switch to the other type of load.
     
  4. awright

    Well-Known Member

    Jul 5, 2006
    84
    7
    No, no, no, no, no! What you have set up is a system to put a hard short across the 240 volt line resulting from a moment of inattention. Setting up a potentially dangerous situation and saying, "I'll be really, really careful not to close the 240 volt switch while the 120 volt switches are closed," is simply setting up an accident waiting to happen (and sooner or later, it will)!

    You will also be drawing 50 amps, not 6.2 amps from the 120 volt line and 25 amps. not 12.5 amps from the 240 volt line.

    Other potential problems are that if one heater's internal thermostatic switch (or even its tipover switch) cuts out on the 240 volt setup its neighbor will be subjected to 160 volts and will soon burn out.

    I would suggest using electric water heating elements in a water bath as inexpensive loads. At $10 to $15 for each element, just wire up two completely independent sets for the two voltages you intend to apply. The elements must never be exposed to air while powered up, so you may have to provide automatic maintenance of the water level depending upon how long you will be applying power. You can obtain 120 volt and 240 volt elements at a wide range of power ratings.

    awright
     
  5. superway

    Thread Starter Active Member

    Oct 19, 2009
    128
    0
    The circuit is drawn either 120vac or 230vac apply separately, not all apply at the same time. each heater is measure about 9.6 Ohm. For 120v, it can used single heater, but for 230ac, it can be connect is series 9.6 Ohm + 9.60 ohm = 19.2 ohm will draw the same current at 120vac because the fan operates 120vac as specs.
     
  6. ifixit

    Distinguished Member

    Nov 20, 2008
    639
    108
    Hi superway,

    The theory is okay for hooking up two heating elements in series as you have planned. However, it would need to be approved by your local electrical authority.

    When an unexpected fault occurs in one of the heaters and causes excessive voltage to be applied across the other heating element in such a way that the fuse doesn't blow, it will cause the heater to overheat and burn down your house.

    Assuming you and your family survive, you will likely have to pay the bill yourself, because your insurance company will discover your unapproved connections.

    Play safe,
    Ifixit
    (Retired firefighter. Beenthere, seen that.)
     
  7. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
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    One sincerely hopes the OP will take this warning to heart.
     
  8. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Wait a sec, now I'm not sure. Is the heater load just to test your product or something more permanent?
     
  9. ifixit

    Distinguished Member

    Nov 20, 2008
    639
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    If you use this connection for testing, donot leave it unattended.
     
  10. marshallf3

    Well-Known Member

    Jul 26, 2010
    2,358
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    Seems like it would be OK as most of those heaters are so well isolated that they aren't even required to have a 3 prong plug. Were I you I'd add a ground wire to each one and find an earth ground for safety's sake.
     
  11. GetDeviceInfo

    Senior Member

    Jun 7, 2009
    1,571
    230
    DO NOT connect this circuit.

    Your 120vac source is typically a hot leg to neutral, while your 240vac is two hots, all coming from a Y source. With this in mind, look at your wiring and see that you could not apply 240vac to the heaters, but rather cause direct shorts. Your amperage numbers are way out of whack as well.

    If you are using one voltage but not the other, then a hard wire, without the switches should be done. But how does that satisfy your blower? Very unlikely any such scheme would pass inspectionl.
     
    Last edited: May 3, 2011
  12. marshallf3

    Well-Known Member

    Jul 26, 2010
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    He may be in a 240V 50 Hz country and picked up some 120V heaters.
    Then again maybe not, why the 120V input?

    Can you give us an idea of what "project" you're wanting to hook this up to?
     
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