Connect with us

12vDC to 24vac module needs modification

Discussion in 'General Electronics Discussion' started by dsmith, Oct 4, 2019.

  1. dsmith

    dsmith

    8
    0
    Jun 28, 2017
    dsmith
    Today
    1
    0
    Hi guys,

    It's been decades since I've done this so helping a little help to jog my brain cells. I have this module where I put in 12VDC (from solar panel) and trying to get 24VAC out 60Hz. I get 12VAC at 60Hz output. (yes pic says 50Hz but adjusted to 60Hz) I put 150ohm 5W resistors at the output terminals (+DC center output is common to both 150ohm resistors) to see the waveform. What do I need to do to get the 24VAC out? Note low power eg 10W usage expected. I think I'm not understanding MOSFET correctly or something.

    Thanks
     

    Attached Files:

  2. Harald Kapp

    Harald Kapp Moderator Moderator

    9,306
    1,889
    Nov 17, 2011
    Use a transformer with a 1:2 winding ratio?
     
  3. duke37

    duke37

    5,231
    718
    Jan 9, 2011
    Or take the output from across the whole primary.
     
  4. dsmith

    dsmith

    8
    0
    Jun 28, 2017
    I think the output should already be 24vac but I only get 12vac. Sounds like I should not be adding any transformers. What might be wrong with existing design?
     
  5. Ylli

    Ylli

    223
    46
    Jun 19, 2018
    Output is 24 V p-p differential (across both outputs). If you look at either output in reference to ground, you will only see 12 V p-p. The two outputs are out of phase so differentially, you have 24 V p-p.
     
  6. dsmith

    dsmith

    8
    0
    Jun 28, 2017
    I get 12V p-p. If I look at output to ground it is 6V either output.
     
  7. Alec_t

    Alec_t

    2,686
    710
    Jul 7, 2015
    What did you use to measure the voltage?
     
  8. BobK

    BobK

    7,633
    1,657
    Jan 5, 2010
    I doubt that would work. The outputs most likely each switches from high impedance to +12V. That is why a center tapped transformer is used.

    Bob
     
  9. dsmith

    dsmith

    8
    0
    Jun 28, 2017
    Measured with both a Fluke multimeter as well as PC based o-scope. Same result
     
  10. Alec_t

    Alec_t

    2,686
    710
    Jul 7, 2015
    Can you post a link to the DC-AC module?
     
  11. dsmith

    dsmith

    8
    0
    Jun 28, 2017
    it was on ebay, no docs just pics, I drew the schematic by tracing the solder path
     
  12. Alec_t

    Alec_t

    2,686
    710
    Jul 7, 2015
    Done a bit of googling. The spec for that module can be found here. This shows the same pic as your second pic.
    Note that the output shown as "0V-" is in fact the +12V rail, if you follow the pcb trace ! :eek:
    That begs the question as to where you placed the probes when you made your measurements.
    I don't see why you are expecting 24V AC from the module.
     
  13. dsmith

    dsmith

    8
    0
    Jun 28, 2017
    Thanks for googling. The measurement is from the one output to other output terminal that's where I get 12VAC. If I measure from output terminal to the 0V- (center) terminal I get 6VAC square wave. Something still seems wrong or I'm really confused about those MOSFET. Can I modify this module to get 24VAC?
     
  14. duke37

    duke37

    5,231
    718
    Jan 9, 2011
    The two halves of the primary are inductively coupled so when one side is pulled to ground, then the other side rises an equal amount above the supply voltage. The transformer needs low leakage inductance between the two halves.

    I have used this system to run higher resistance speakers, Not a great success due to the diddy transformer having high resistance windings.

    There will be voltage drop across the switches and any rectifying diodes so you will not achieve quite double the input voltage.
     
  15. Alec_t

    Alec_t

    2,686
    710
    Jul 7, 2015
    That's what you should get. Here's a sim, where S1 and S2 represent the FETs :
    InverterModule.png

    Edit: If you replace the resistors with the two halves of a centre-tapped transformer winding then, for the reasons Duke gives, you should get close to 24VAC between A and B.
     
    Last edited: Oct 6, 2019
  16. dsmith

    dsmith

    8
    0
    Jun 28, 2017
    Thanks Alec_t for running that sim. That waveform picture is what I expected but that's not what I get. Where you have V(0V-, A) showing a 12V swing I only get 6V swing. Same for V(0V-,B), Your resultant V(A,B) gives 24V swing whereas I only get 12V swing.
     
  17. duke37

    duke37

    5,231
    718
    Jan 9, 2011
    A 12V swing will show as 6V AC i.e. +/- 6V on an analog meter.

    What is the load? Is it a rectifier which selects the peak?
     
  18. Alec_t

    Alec_t

    2,686
    710
    Jul 7, 2015
    As Duke says, 6VAC = 12V peak-to-peak for a square-wave.
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-