pcdcox Induction PCB

Discussion in 'The Projects Forum' started by Pcdcox, Dec 1, 2015.

  1. Pcdcox

    Thread Starter New Member

    Nov 27, 2015
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    I will try again to explain what I want to do. My induction PCB operates at 220/240 VAC which is applied at CN1 in my circuit. I want to convert to 110 VAC for the US market. I have no problem with the low voltage side of my circuit but I need assistance with the high voltage side.The induction coil which I use to heat metal instruments connects to CN2/CN3 in my circuit. When the instrument is inserted in the coil an eddy current is generated and heats it. This works fine with 220 volts but not for 110 volts. I need to know what components to change to get the same results as 220 V. I thought is was a simple matter of reducing the value of R1 and R4 to get the same VA at CN2 and CN3 but it turned out to be not that simple. I would appreciate your help.
     
  2. ian field

    Distinguished Member

    Oct 27, 2012
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    Its the same schematic you posted before which still violates AAC rules.

    The circuit you need to modify for 120V is pretty much the same as a compact florescent bulb'

    As I already suggested - search the net for CFL schematics to see how they do it in 120V countries.
     
  3. Pcdcox

    Thread Starter New Member

    Nov 27, 2015
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    Hi Ian, It is the same schematic but my request and wording is different. There is a 12 VDC transformer (T1) in the circuit as per AAC rules.If I remove the transformer from the PCB circuit I will get my 12 volts from a power supply that has a transformer and transforms 110 and 220 volts to 12 VDC. How can that be against the rules.?
    I can't get 12 volts from the mains supply without employing a transformer.
    The high voltage side of my circuit involves heating a metal instrument by induction I appreciate your suggestion but I don't think it is relevant.
     
  4. ian field

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    Oct 27, 2012
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    I've told you twice now where to find a circuit example that will solve your problem.

    If you choose to ignore it - that's your problem.
     
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  5. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    The connection from the four diodes D1 to D4 to the mains connection Cn1 is NOT ALLOWED, so edit your drawing and put a Transformer in-between, then your thread will be ok.
     
  6. ian field

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    Oct 27, 2012
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    The TS could convert that circuit by adding 2 electrolytic capacitors. Describing it would be adding to the infringement of AAC rules.

    Twice now I've indicated where to find an example circuit - but the TS doesn't want to know.
     
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  7. Dodgydave

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    Jun 22, 2012
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    You mean a split bridge rectifier using two diodes replaced by two capacitors, voltage doubler cct used in atx psus, et al...:eek:
     
    Last edited: Dec 1, 2015
  8. ian field

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    Oct 27, 2012
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    Its used in a lot more than ATX PSUs - probably 90% of PSUs capable of working on 120V mains have 2 reservoir electrolytics - they can be converted to 220V simply by moving a fly-lead to a different pin.

    Although in the past decade, there's been a big increase in wide duty cycle range PSU chips that can drive the chopper transformer anything from 90 - 265V with no jumper or voltage selector.

    A firm I did repairs for had a few schools contracts - a more or less steady stream of PC PSUs that vandals had slid the 120/220V switch over. Any that were repairable, I removed the wires from that switch before wrapping up the job.
     
  9. Pcdcox

    Thread Starter New Member

    Nov 27, 2015
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    Why.? It's an AC circuit and Wendy has said that AAC have nothing against AC circuits.
     
  10. Dodgydave

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    Jun 22, 2012
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    Its a live connection to mains , put a Transformer in between the bridge rectifier diodes D1to D4, or your thread will be closed down again!!!!
     
  11. ian field

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    Oct 27, 2012
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    "peeing into the wind" springs to mind.
     
  12. Pcdcox

    Thread Starter New Member

    Nov 27, 2015
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    Please see attached a revised circuit diagram.
     
  13. Dodgydave

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    Jun 22, 2012
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  14. Pcdcox

    Thread Starter New Member

    Nov 27, 2015
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    Thank you for the information.
    Can you specify the capacitor values.?
     
  15. Dodgydave

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    Jun 22, 2012
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    Usually in atx psus, they're about 330-470 uF, at 450V dc
     
  16. Pcdcox

    Thread Starter New Member

    Nov 27, 2015
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    Brilliant, thank you.
    I will let you know how it goes.
     
  17. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Another option, since you have 1/2 the voltage swing across your inductor, is to change the inductor value to get the same current through it you used to get at 220 Vac.

    ak
     
  18. Pcdcox

    Thread Starter New Member

    Nov 27, 2015
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    Can you explain in more detail please.Do you mean change the values of the diodes in the diode bank.?
     
  19. ian field

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    Oct 27, 2012
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    You're thinking of the ones with PFC front end - its basically a boost converter with no input reservoir electrolytic. The total voltage rating of the reservoir capacitors would normally add up to about 385 - 400V, the PFC is a modified boost circuit so the reservoir *IT* charges needs about 450V rating.

    The older types could switch in a voltage doubling arrangement to run on 110V instead of 220V.

    The reservoir electrolytic was split into a series pair across the DC terminals of the bridge.

    The 110V switch was nothing more than just a switch, it connected the tap between the 2 series capacitors to one AC arm of the bridge.

    In that case, the 'spare' diodes remain in circuit while the capacitors are simply added to them.
     
  20. Pcdcox

    Thread Starter New Member

    Nov 27, 2015
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    Sorry AnalogKid "the penny has dropped",to get the same current with half the voltage would I have to double the number of turns on the inductor.?
     
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