Putting Two Transformers in Series

Discussion in 'General Electronics Chat' started by sjgallagher2, Aug 4, 2015.

  1. sjgallagher2

    Thread Starter Member

    Feb 6, 2013
    111
    7
    Hey all,
    This question is giving me a headache, and I need some practical advice. I need a proof of concept that I can put two separate transformers in series like so:
    PRIM1 : SEC1 -> PRIM2 : SEC2 -> output (input x turns ratio1 x turns ratio2)
    I quickly ran a spice simulation and got normal results from a single transformer (10:1) and two transformers in series (5:1, 2:1), pictured below:
    [​IMG]

    [​IMG]
    So the theory obviously checks out, no surprises there. So practical considerations: If both the transformers are rated properly for whatever input/output voltage I have in mind, and they both share the same VA rating, will this really work. Here are some example transformers, a 5:1 and a 1:1 (both rated at 60Hz and 40VA)
    http://www.digikey.com/product-detail/en/4-1611453-7/PB1649-ND/1128437
    http://www.digikey.com/product-search/en?KeyWords=4000-60E07K999-ND&WT.z_header=search_go
    Would you feel comfortable putting these two transformers in series as depicted? Applications aside, as I do not know the application for this configuration but am only researching.
    Thanks in advance.
    Sam Gallagher

    PS I'm having difficulty with pictures so Ill attach them.
    Transformer1.PNG Transformer2.PNG Transformer1.PNG Transformer2.PNG
     
  2. ranch vermin

    Member

    May 20, 2015
    85
    2
    Wouldnt transformers not need a connection and just travel through the air through the flux field?
     
  3. dl324

    Distinguished Member

    Mar 30, 2015
    3,242
    619
    Hi,

    It's very common to put primary windings in series for 120/240VAC switching. Less common for secondaries, but I've seen it done (e.g. to make complementary supplies). You just need to pay attention to output phase and current rating.
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,515
    2,369
    A misconnection on series secondaries just results in non or lower output, if in parallel you can short them out, so the detection sequence is different.
    The Va rating will be for the lower rated transformer.
    Max.
     
  5. sjgallagher2

    Thread Starter Member

    Feb 6, 2013
    111
    7
    Just to be clear, I have two transformers, separate components. The input (say, 120VAC) goes into the primary of TX1, and the secondary of TX1 is connected to the primary of TX2. The output is taken from the secondary of TX2. Just to avoid confusion, because I'm uncertain what Dennis is referring to by 'putting secondaries in series' since I'm not putting the secondaries in series, am I?
    Sam Gallageher
     
  6. #12

    Expert

    Nov 30, 2010
    16,261
    6,768
    The Power Company does multiple step-downs and so do I.
    I use a Variac to run a 120:24 transformer and use that to run a microwave oven transformer, and then rectify that to get DC voltages in the higher ranges, like 400 VDC.

    Then, for a different job, I use the 208 volt primary winding of a 24VAC transformer by applying 125 VAC. The result is 14.4 volts which I wire to buck the power line voltage down to 110.6 VAC so my outdoor lights don't burn out every 3 years. When their inductor is fed a few percent LESS voltage than it was designed for, the bulbs often last 10 to 12 years.

    You can play mix&match with transformers all day if you are careful to calculate their limits so you don't over-heat them.
     
  7. dl324

    Distinguished Member

    Mar 30, 2015
    3,242
    619
    There was a problem with the pictures when I read your original post. You're using them as multiple step down as #12 referred to. Maxheadroom and I interpreted your query as can you connect the windings in series...
     
  8. crutschow

    Expert

    Mar 14, 2008
    12,993
    3,229
    You can certainly feed the secondary output of one transformer to the primary input of another as long as its primary voltage rating and the current rating of either transformer is not exceeded.
     
  9. Ggmadevent

    New Member

    May 12, 2016
    1
    0
    Thank you for that reply, crutschow.
     
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