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Quick transformer question

Discussion in 'General Electronics Discussion' started by eletronic, Feb 25, 2013.

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  1. eletronic

    eletronic

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    Feb 25, 2013
    I'm working a little DIY project I bought while I was in Japan.

    The only problem is I'm now in the US.

    The device's manual says it's rated for 12-15VAC input.
    The transformer that came with the kit is rated at 100VAC Input @ 50-60Hz and puts out 12VAC 400mA.

    So here's what I'm thinking... In Japan they use 100V. In the US we use 120V.
    My devices is rated to take in 12-15V. So if I plug this transformer into the wall here in the US it will put out 14.4VAC and I'll be within my 12-15VAC range (as in: 100V*1.20=120V and 12V*1.2=14.4V).

    Am I correct in my thinking or would it be safer to buy a 120V rated power adapter?

    And will this change over also increase the amperage or will that remain at 400mA?
     
    Last edited: Feb 25, 2013
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    11,316
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    Nov 17, 2011
    The transformer should work on 120V.
    Of course it would be safer to use a 120V transformer.
    The amperage will not change noticeably.
     
  3. eletronic

    eletronic

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    Feb 25, 2013
    Thanks for the fast response Harald!

    I plugged it in and it powered up fine, are there any symptoms I should look out for that would indicate I'm overpowering the unit to a point that its being damaged?
     
  4. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,271
    Nov 28, 2011
    Your 100V transformer will be fine.

    Edit: If you're worried, measure the AC voltage coming out of the transformer and make sure it's not more than 15V.

    Upload the schematic of the kitset circuit and we can tell you how critical the voltage will be.
     
  5. Harald Kapp

    Harald Kapp Moderator Moderator

    11,316
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    Nov 17, 2011
    Smoke?
    Funny smell?

    If space allows, add a 375mA fuse in series with the low-voltage side of the transformer.
     
  6. eletronic

    eletronic

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    Feb 25, 2013
    I tested the transformer with a multimeter, it came back as 17.4V :eek:

    I know that's not a terribly huge amount over 15V, but still I'm just gonna play it safe and buy a 12V adapter at the hardware store today.

    Anyways, thanks for the help Harald and Kris! :)
     
  7. john monks

    john monks

    693
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    Mar 9, 2012
    One point of interest here. The iron core transformer is not all that forgiving. For example when a typical 120VAC transformer is run at 140VAC the core is intering saturation and the transformer heats up. Why eletronic is getting 17.4V is a mystery to me. It could be that his line voltage is higher than 120VAC. I just measured the line voltage here in San Rafael, California an I got 127VAC. So that would be even of more concern to me.
     
    Last edited: Feb 25, 2013
  8. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,271
    Nov 28, 2011
    Perhaps the "12VAC" transformer he's using is specified as 12VAC at full rated load current, and its output voltage will be higher with no load or a lesser load.

    I thought there wouldn't be an issue going from 100 to 120V. I stand corrected. Thanks John.
     
  9. Young

    Young

    47
    0
    Feb 6, 2013
    Maybe add some zener diodes or resistors to reduce the voltage,but i will advice getting the adapter
     
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