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Change Voltage Transformer

  1. Jun 19, 2014 #1
    Hello everyone!

    Firstly, I have very basic knowledge of pcb design and in electrical engineering in general :confused:
    I want to ask you if I want to change a 10 pin transformer into a 8 pin one. Would that effect the quality or sth? what consequences does it have ? are pins with more quality better ? or it all depends on the input in the schematic design??

    This is the transformer datasheet!
    I want to replace (BEPC-13-1110CPH)(10pins), with (BEPC-10-118GA)(8pins)!

    Thanks a lot in Advance!!
  2. jcsd
  3. Jun 19, 2014 #2


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    The core you nominate is a newer "surface mount" style more suited for automatic assembly than the older "pins through hole" style.

    You are also selecting a smaller core with slightly less magnetic section. That may be a problem if the application has sufficient current to causes magnetic saturation of the core. For small signals you may get away with it, but for power it may be a real problem.
  4. Jun 19, 2014 #3


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    The datasheet is for a core with 10 or 8 pins, not a transformer. If you need 10 pins, you need 10 pins. If you only need 5, then the only issue is the magnetic characteristics. The number of pins means nothing from an electrical perspective.

    What are you doing with it?
  5. Jun 20, 2014 #4


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    “I want to replace BEPC-13-1110CPH (10pins), with BEPC-10-118GA (8pins)”
    These have different sizes, a different number of pins and a different mounting technology.
    They will fit different ferrite cores.

    This document lists the ferrite cores that will fit those bobbins. They have different characteristics.

    For the ferrite core to stay the same, you would need to replace the BEPC-13-1110CPH with surface mount BEPC-13-1110GA.
    These are the available ferrite cores. Part number and AL value.
    PC45EPC13-Z 870±25%
    PC45EPC13A40 40±4%
    PC45EPC13A63 63±5%
    PC46EPC13-Z 1050±25%
    PC46EPC13A40 40±4%
    PC46EPC13A63 63±5%

    Changing from size BEPC-13- to size BEPC-10- would require a different size ferrite core.
    You would need to select one of these cores with a similar AL value to the original.
    PC45EPC10-Z 1000±25%
    PC45EPC10A40 40±7%
    PC45EPC10A63 63±10%
    PC46EPC10-Z 1060±25%
    PC46EPC10A40 40±7%
    PC46EPC10A63 63±10%
    But then magnetic saturation of the ferrite core may be a problem.
  6. Jun 20, 2014 #5
    Hi Baluncore, how can I know if its a small or big signal ? or to know if the current cause saturation ?
  7. Jun 20, 2014 #6
    How can I know if magnetic Saturation would or would not be a problem? and do you see any of the options above match with Al values ?

    Thanks a lot
  8. Jun 20, 2014 #7

    jim hardy

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    In transformers it's generally the volt-second product that saturates the core.
    If you have enough turns a small core will support a large volt-second value because the inductance is large enough to keep the flux reasonable. Remember inductance is flux linkages per ampere, /i.
    But a lot of turns implies small wire
    so your core has to be physically big enough to accommodate the requisite number of turns of the wire size that'll both provide necessary inductance and handle the current. That's why high power transformers are bigger than low power ones, they need bigger windows for their wires.

    To aid in choosing a core manufacturers publish a number relating the number of turns to the inductance

    where L = n2AL

    It is one of those 'shortcuts' used by transformer designers.

    Search around for some transformer design articles. Coilcraft used to have some good ones as did magnetics inc.

    A search on 'magnetic design AL parameter' turned up several for me; here's a likely spot to begin.


    Transformer design isn't hard it's just been streamlined to the point it looks unfamiliar.
  9. Jun 20, 2014 #8
    Hi Guyss!!
    Do you recommend a freelancer engineer, who can help me solve this for an average amount of payment ?

  10. Jun 20, 2014 #9

    jim hardy

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    Oh, c'mon, just do it.

    Baluncore said it, when picking a new core match AL so inductance stays same
    and you must have enough room for the wires , so match window area too
    and all the dimensions look to be on your datasheet

    if you cant match or improve those two parameters then you'd best not change the transformer.

    time to increase your understanding of transformer basics ?

    I'm no transformer designer but i feel it's important for an EE to at least understand them.
    Brush up your basics - flux, amp-turns, dø/dt.
    Grab this opportunity. Surely there's an old timer in your workplace who'd take kindly to being asked to look over your work.
  11. Jun 20, 2014 #10
    Thanks you so much for the advice Jim. The thing is I am an Industrial engineer, with deeper mechanical engineering background, and basic electrical knowledge. Although I am restricted by time, but I will take your advice, and try to get good results. Can I show you the result here ?

  12. Jun 20, 2014 #11

    jim hardy

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    It wasn't clear to me from the catalog just what core goes with what bobbin, but i didn't work real hard digging at it either.

    It did appear that the EPC 10 and EPC 13 cores have different AL values with no air gap
    but with air gap they're almost the same. But it didn't say how much air gap.
    Do you guys assemble the transformer yourself? Or is it a bought item? If the latter a quick call to TDK's support group should answer whether they can provide it in your desired smaller footprint.

    If you assemble it yourself , find your transformer guru and get him talking about how he selected the parts.
    If you appear to have prepared yourself and are inquiring rather than challenging him surely he'll be forthcoming - i know i would. You two might be able to test some real parts on the bench.

    old jim
  13. Jun 20, 2014 #12
    Yes, it is a bought item. I will try to contact Tdk, and see what is possible! Thanks a lot old jim ;)! Its wonderful dedicating your time to answer my questions :)!
    best of luck
  14. Jun 20, 2014 #13

    jim hardy

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    Thanks go to Baluncore - i had missed this line in his post
    armed with that and an understanding of AsubL you can converse intelligently with your supplier.

    best of luck to you

    As an engineer, always strive to broaden your understanding of basics. Most folks don't get a chance to delve into magnetics..

    end of nag

    old jim
  15. Jun 20, 2014 #14
    Yes, True old Jim. I know this might sound wired, but I want to send you a gift for helping me, I appreciate your help a lot, can you accept it from me please?

  16. Jun 20, 2014 #15

    jim hardy

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    The kind words are plenty, thanks.

    "Pay it forward" - help somebody out with your expertise.

    Baluncore and mBigGuy put the answer out there - all i did was assist with translation. You might click 'thanks' on their posts.

    old jim
  17. Jun 21, 2014 #16


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    did you use the THANKS button at the bottom of Jim's post ?

  18. Jun 21, 2014 #17
    Yes Dave, I did
  19. Jun 21, 2014 #18
    Hello Jim, mBigGuy, Baluncore !

    I found a transformer called Bobbin : EEM12.4. vertical. Its core is EEM12.4 (ferrite material TDK PC40 or equivalent)! Do you have any clue how would I find its data sheet ? I cannot find it!

    Jim, I will pay it forward, of course!

    Thanks a lot guys, again :)

  20. Jun 21, 2014 #19

    jim hardy

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  21. Jun 21, 2014 #20


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    Staff: Mentor

    heathheath -- what is the application for this transformer?
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