Variac leads?

Discussion in 'General Electronics Chat' started by skoot66, Aug 11, 2013.

  1. skoot66

    Thread Starter New Member

    Aug 11, 2013
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    I have a variac, but the only output connection is a standard plug. I need to run power to a circuit board. Can I just take an extension cord, cut off the male plug, and attach alligator clips to the wires?
     
  2. Metalmann

    Active Member

    Dec 8, 2012
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    What gauge is the extension cord wiring?
     
  3. skoot66

    Thread Starter New Member

    Aug 11, 2013
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    Could be any, I don't have a particular cord in mind.
     
  4. studiot

    AAC Fanatic!

    Nov 9, 2007
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    This site definitely does not recommend using alligator clips in this manner.

    There are proper temporary connection methods

    Keynector
    Safebloc

    amongst others.
     
  5. #12

    Expert

    Nov 30, 2010
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    I suspect that a plug on a Variac is not an output, but the input.
     
  6. Relayer

    New Member

    Jan 1, 2013
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    Most Variac's are NOT isolated types and I would think twice about using it to power up a circuit board.
    Regards,
    Relayer :D:D:D
     
  7. DerStrom8

    Well-Known Member

    Feb 20, 2011
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    Yes, I expect he meant "socket" :p

    You haven't mentioned what this circuit board is for. You usually shouldn't connect a variac to a professionally-manufactured board, as they are not designed for such a huge variation in voltage. You could very easily destroy it.

    We really need more information before we can help you further.

    Matt
     
  8. skoot66

    Thread Starter New Member

    Aug 11, 2013
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    The boards are all part of an audio amplifier project. I need to test my power supply boards, as well as the amplifier boards. I will need to run 110v to the power supply boards and 63v to the amplifier boards to test them. The amp is dual mono, both boards are running of 45v secondaries of individual toroidal transfos.
     
  9. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Mine has a standard 15a socket for the output side.
    Max.
     
  10. LDC3

    Active Member

    Apr 27, 2013
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    That's a hefty variac. Most variacs limit the current to below 8A.
     
  11. MaxHeadRoom

    Expert

    Jul 18, 2013
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    The socket is rated 15a, fused much less.
    Max.
     
  12. GopherT

    AAC Fanatic!

    Nov 23, 2012
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  13. Meixner

    Member

    Sep 26, 2011
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    As Relayer said most Varaics are not isolated, You stand a good chance of frying your boards if you connect them directly to a Varaic.
     
  14. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    Frying yourself too, Sparky!
     
  15. studiot

    AAC Fanatic!

    Nov 9, 2007
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    Applying a reduced voltage via a variac to a circuit is a common and reasonable service or development technique to reduce the chances of catastrophic failure due to circuit malfunction.

    It must be carried out safely, however.

    Further it will not work with all types of circuit. Many require the correct AC input voltage.

    The type of socket outlet does not determine the available current.
    This should be stated by the manufacturer since it is a function of winding wire characteristics, and should not be exceeded. The max power (VA really) available is the product of the max dial voltage and max current. Remember the max dial voltage may be higher than the mains input.
     
  16. sheldons

    Well-Known Member

    Oct 26, 2011
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    testing the power supply section on the AC INPUT SIDE will be ok with your variac but DO NOT connect it to the amplifier board direct as you will damage the board as it requires a dc supply not an ac supply,unless you are VERY CAREFUL and connect it via the rectifier ip on the amp and dont turn the variac up too high....but it IS NOTat all the correct way to do this.....plus most amps may require a split rail supply.
    Also remember a variac is by no means mains isolated so the normal SAFE RULES for servicing still apply and unless there is a means of safe mains isolation NO scopes to be connected if the supply is a switched mode type unless using an isolation transformer.....
     
  17. skoot66

    Thread Starter New Member

    Aug 11, 2013
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    Oh no, that's not what I meant, I should have been more clear. I will test the power supply section with power direct from the variac, then hook up the amplifier boards to the power supply boards, and test them with the power supply boards plugged into the variac.
     
  18. studiot

    AAC Fanatic!

    Nov 9, 2007
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    I realise that and that's OK, provided you don't use alligator clips to the psu boards from the variac. What if they slip off and flail about?

    It is easy enough to rig up (solder or whatever) some flying leads from the psu board and another flying lead from the variac and join them with a proper temporary connector eg a screw terminal block.

    You have put a deal of effort into creating the boards so finish the job properly, not hastily.

    I have a keynector permanently available to plug into my variac.
     
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