Convert 120Volt soft starter to a 220Volt soft starter

Discussion in 'General Electronics Chat' started by lubnaan90, Feb 7, 2012.

  1. lubnaan90

    Thread Starter Active Member

    Jan 13, 2010
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    Greetings to all the Readers,

    Here is a Schematic of a Soft starter for Toroidal transformers that was designed to work with 120v 60hz mains power.

    What changes should be made in this circuit for safe operation with 220v/50hz mains supply?

    Any useful Comments, advises or Recommendations will be deeply appreciated.

    Best regards.
     
  2. mik3

    Senior Member

    Feb 4, 2008
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    Don't think this realy will ever turn on!
     
  3. lubnaan90

    Thread Starter Active Member

    Jan 13, 2010
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    And why is it that you think this way?
     
  4. tom66

    Senior Member

    May 9, 2009
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    Such a circuit is dangerously non-isolated BUT...

    the cap should be changed to 150n 400V

    and the 10R/5W should maybe be 22R/5W.

    Use a transformer, far better and safer.
     
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  5. mik3

    Senior Member

    Feb 4, 2008
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    Wrong estimation!
     
  6. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    I would only say that the relay will not turn on under any circumstances if I had it's specifications.
    For sure the capacitors voltage rating needs to be increased.

    Where is the output going to? Maybe there are better/easier ways to do what you want.
     
  7. SgtWookie

    Expert

    Jul 17, 2007
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    Hello again, Lubnaan90.

    First it would be helpful to know what will be the DC coil voltage and coil resistance of the relay that you wish to use.

    For example, if it happens to be a 12v 600 Ohm coil, the circuit can be used as-is with 220VAC 50Hz, and the relay will engage about 0.75 seconds after the power is turned on.

    However, I don't know what relays you can buy where you live. If you can get a relay that has a coil rated for somewhere between 6VDC and 24VDC, and perhaps 400 to 1,500 Ohms (increasing as the voltage goes up) then I can help you to "fine tune" the schematic.

    Also, if you want more of a delay than 3/4 of a second, then you should tell me.

    The most important thing is that the contacts are rated for the voltage and current you will be putting through the contacts.
     
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  8. SgtWookie

    Expert

    Jul 17, 2007
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    It seems that most people are missing the fact that the output will be connected to the primary side of a toroidal transformer. This circuits' function is to provide a "soft start" so the filter caps have some time to charge before full mains voltage is applied to the transformer primary.

    Which cap? C1? 250VAC minimum would be enough. As for the capacitance, that depends upon the relay, which our OP has yet to select. The larger C1 is, the higher the output voltage.

    Well, that also depends on the transformer and the expected load on start-up. We don't know what the original design was for - except 120V 60Hz instead of 220V 50Hz.

    That's what this circuit feeds the primary of.
     
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  9. SgtWookie

    Expert

    Jul 17, 2007
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    Actually, if the relay had a 12VDC 600 Ohm coil, the circuit could be used as-is.
    That wouldn't hurt. 350VAC rating would be fine.

    The output is connected to the primary of a toroidal transformer, which has to start charging filter caps via a bridge upon power-up. This circuit throws some resistance in the path to decrease the peak current on startup.
     
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  10. SgtWookie

    Expert

    Jul 17, 2007
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    OK, I just found the relay in your other thread; the Omron G6RN-1 DC24. The coil is 2620 Ohms. If C1 is changed to 150nF/0.15uF, the relay should work just fine, and it will have a delay of about 3 seconds before the relay closes.
     
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  11. lubnaan90

    Thread Starter Active Member

    Jan 13, 2010
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    Hello Again SgtWookie,

    Many Thanks for your helpful quotes. My apologies for i couldn't reply instantly when you asked about the Relay due to the time difference between our locations.

    Well, Since you found out your self about the relay i am going to use (Omron G6RN-1 DC24) and suggested to use a 0.15uf cap, i have two options...
    1) CBB21 0,15uf 400v 10%
    2) CL-11 0,15uf 630v 10%

    Which one of the above will be best suited?

    I am using 2 x 600Watts Toroidal Transformers.
     
  12. lubnaan90

    Thread Starter Active Member

    Jan 13, 2010
    196
    2
    For Others who think that this circuit will or does not work, sorry to disappoint but the circuit has already been built and tested on 120volt supply and seems to work perfectly fine. Actually you can check on ebay it is also being sold as a kit here http://www.ebay.com/itm/Soft-starting-switch-full-kit-power-amplifier-/320429434259
    (This is a 220volt version based on the same schematic i have posted in this thread)
     
  13. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    I do not see any reason why this circuit won't be able to convert to a 220VAC version.
     
  14. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    This "other thread" and sometimes "other forum" thing isn't really helpful. These OPs are lucky that there are people like Sgt or AG who keep track of everything.
     
  15. SgtWookie

    Expert

    Jul 17, 2007
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    No problem -- I remembered the other thread, and wondered what happened to it; that's when I discovered the relay part number, which helped me find the datasheet.

    well, they are both poly metal film. The first one is 400v and less expensive, so I would use that one.
    OK, so that is about 5.45 Amperes current at the rated output.
     
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  16. lubnaan90

    Thread Starter Active Member

    Jan 13, 2010
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    So what is to be done with the resistors on the board. Should i change them or let them be as it is ?

    Oh, by the way, i found this soft start kit on Ebay during my research and found out that it is based on exactly the same circuit i started this thread with. I have posted some pictures of that board and the schematic i took from the ebay page.

    This board from eBay is meant for operation with 220v power supply, by looking at the picture with the components and the schematic, it seems that the Manufacturer has used a 0.56uf Capacitor & the resistor is a single 68Ohms/7 W, rest all other components seems to be the same as in the schematic i posted earlier.

    Best Regards.
     
  17. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    Note that you may still experience inrush current - when there is a voltage drop of the input voltage for a few periods. The relay stays on for a certain time because the capacitors discharge through it even without input AC voltage.

    When voltage comes back the relay contacts are then still closed.

    If you wanted to avoid this the relay would need to be turned off faster, detecting the missing input voltage.
     
  18. SgtWookie

    Expert

    Jul 17, 2007
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    You can increase the 10-ohm resistors to 15 to 18 Ohms if you would like. However, 220v/40 Ohms = 5.5 Amperes; the same as the toroids under full load. They really don't need changing, but it certainly would not hurt to increase their wattage rating.

    Here is the datasheet for the Songle SLA-24VDC-SL-C relay:
    http://www.cytron.com.my/usr_attachment/Songle SLA.pdf
    The 24 volt relay has a 660 Ohm resistance. The one you are using has a much higher resistance; 2.2k or so. If you tried to use the larger cap with your relay, you would burn it up, along with the two 470uF caps.

    If you don't follow my recommendations, you will have problems.
     
  19. lubnaan90

    Thread Starter Active Member

    Jan 13, 2010
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    Hello SgtWookie,

    Of course i won't neglect your recommendations, due to my past experience and sucess in projects by using advises from you and some of other members, I surely trust your recommendations.

    So here is the final conclusion:
    1) I will use the capacitor CBB21 0,15uf 400v 10%
    2) I will use the Resistors with the same value but with more wattage, say for e.g. Resistor SQP-10W 10 Ohms x 4 or probably raise them to SQP-10W 15 Ohms x 4 (Incase 10 Watts is not available i might use 15Watts Resistors, Is that ok?)

    Thank you...
     
    Last edited: Feb 8, 2012
  20. lubnaan90

    Thread Starter Active Member

    Jan 13, 2010
    196
    2
    Hello SgtWookie,

    Can i use a single SPQ-20W- 47 Ohm Resistor instead of 4 x 10 Ohm resistors?
     
    Last edited: Feb 10, 2012
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