220 VAC to 110 VAC

Discussion in 'General Electronics Chat' started by boatsman, Aug 27, 2010.

  1. boatsman

    Thread Starter Senior Member

    Jan 17, 2008
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    383
    In a microfilm developing machine I am using the terminals of the air heating coil have corroded and I need to replace the coil. The coil is rated at 1000W 220 VAC. I have a similar older machine with a heating coil in as new condition. The snag is that it is rated at 1000W at 110 VAC. For various reasons I am unable to use a stepdown transformer or to place a very large resistor in series with the coil. Is there anyway I can use a large diode or Triac to solve the problem? Thanks, boatsman.
     
  2. AMIT_GOHEL

    Member

    Jul 13, 2010
    67
    7
    1capacitor and 1reg connected in cascaded.
    connect it with series in supply.

    By changing the values of R & C ,you can get the required voltage...

    One thing i want to tell u that i'm not fully sure about it..
    i've seen similar one in night lamp(230v ac to5v ac).

    Regards....
     
  3. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    2,574
    230
    Those circuits are meant to step-down voltages at a few milliamp current levels, not several amps. For phase shift step-down of 110VAC/60Hz/1KW from 220VAC you would need a 25000uF/350V non-polarized capacitor. That would be bigger than a step-down transformer.

    The most efficient conversion, size-wise, would be an AC-DC switch-mode power supply. But, I don't know if they exist off-the-shelf.

    Ken
     
  4. SgtWookie

    Expert

    Jul 17, 2007
    22,182
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    Well, if you're in the USA or Canada, then it's 240VAC/120VAC @ 60Hz.

    1kW @ 240VAC = 4.167 Amperes
    1kW @ 120VAC = 8.333 Amperes

    So, if you go to the lower voltage unit, you'll double your current requirement.

    A 240v:120v 1kVA transformer would be the most efficient and reliable way to adapt the lower voltage heating coil to your unit.

    Have you attempted to clean the corrosion from the terminals of the original heating coil?

    I've found that muriatic acid (pool acid; dilute hydrochloric acid; available at swimming pool supply stores) works quite well for removing corrosion from brass/copper terminals, and is just a few bucks a gallon. Be careful with it though; you really have to use it outside; don't breath the fumes, and don't get any on you; wear rubber gloves and eye protection. It will permanently etch concrete, and damage most other surfaces. Always keep a full bucket of fresh water handy in case of spillage. A tablespoon or two of baking soda mixed in the water will help a great deal to neutralize the acid.

    Immerse the terminals into full-strength muriatic acid for 30 seconds or so, and then immediately rinse in plenty of fresh water. If there is still some corrosion, repeat.
     
  5. marshallf3

    Well-Known Member

    Jul 26, 2010
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    How hard would it be to convert the rest of the machine to run off of 120V? It there isn't much else to it that may be the way to go.
     
  6. SgtWookie

    Expert

    Jul 17, 2007
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    It may simply not be practical to convert the entire machine to 120v. Doing so would double the losses in the wiring of the building from the service panel to the equipment. If the existing wiring were adequate for powering with 240VAC (with, say, 50% overcapacity) then it may not be adequate for service with 120V at the same VA.

    I suggest that a licensed electrician should be consulted prior to attempting such a modification. It would be very difficult to accurately discern remotely if such a conversion would be practical without incurring a large expense for upgrading the buildings' wiring.

    A 1kVA 2:1 transformer would likely be far more economical.
     
  7. tom66

    Senior Member

    May 9, 2009
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    With heating elements it is often OK to just put in a power diode in series with the load. This only conducts during the positive cycle, halving the effective power dissipation, which may be enough to do what you want.
     
  8. boatsman

    Thread Starter Senior Member

    Jan 17, 2008
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    383
    Thanks for replying. This is what I had in mind but I didn't know if it was feasible. I think I would need 400 volts PIV and about 15 amps. I had the idea that using a diode the power would only pass in one direction and would be blocked every half cycle thereby effectively giving me 110 volts. As it's a heating device it shouldn't matter that the current is switched off every half cycle, but I wasn't sure if it was feasible. When I wrote that the terminals were corroded I should have said that there was nothing left to clean up or to solder or weld.
     
  9. tom66

    Senior Member

    May 9, 2009
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    Yes; the power dissipation is reduced by half because it is only getting a duty cycle of 50% or so. Care however has to be taken to ensure any insulation on the wires is rated for 230V (325Vd.c.) as the peak voltage will still be 325V, or so.
     
  10. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    2,574
    230
    Also, that the wire is rated to carry 8A rather than 4A.

    Ken
     
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