Transformerless DC to AC inverter to 24VAC

Discussion in 'The Projects Forum' started by Belteshazzar, Mar 30, 2010.

  1. Belteshazzar

    Thread Starter Member

    Mar 16, 2010
    34
    0
    Hi,

    I am looking for a transformerless 12VDC to 24VAC inverter circuit able to
    hold at least 2 to 3 amps. (50-75Watts)

    Can anyone help me with this?

    Has anyone seen a schematic or knows how to design one?

    Don't need PWM to create a nice sine wave, although it would be nice, a square wave is fine.

    I am willing to go from 24VDC or even 48VDC if necessary to get a transformerless option.

    If I understand correctly, the easiest way is from 48VDC because DC get cut to about half the voltage to form a AC wave without a step-up circuit?

    Would prefer to invert from 12 or 24 though.

    Thanks
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Please don't open multiple threads on the same topic.

    This is not a chat room. A sensible reply may take some hours or longer.
     
  3. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,754
    760
    You have to use a high power amplifier with batteries.
    Rather odd thing you asking for, don't you think?
     
  4. ifixit

    Distinguished Member

    Nov 20, 2008
    639
    108
    Just use a 100W car audio amplifier driven with a nice sinewave of low power.
     
  5. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,754
    760
    Just as I was about to say.

    Inject a 50Hz Sine wave into 500W car amp and you will get a nice AC sine wave with a lot of LOSS & HEAT :D
     
  6. rjenkins

    AAC Fanatic!

    Nov 6, 2005
    1,015
    69
    Just a full bridge (H-Bridge) driven from a square wave.

    That would give 24V P-P as long as your load is floating, as both ends need to be driven.
     
  7. kubeek

    AAC Fanatic!

    Sep 20, 2005
    4,670
    804
    Not really, 24Vpp is very different from 24VAC.
    24VAC is 48Vpp (in case of a square wave).
     
  8. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    5,448
    782
  9. Belteshazzar

    Thread Starter Member

    Mar 16, 2010
    34
    0
    Thanks folks for all your replys.

    Interesting article, thanks tnk. I'll chew on it for a little while although it might be a little too advanced for me.

    I don't understand beenthere's coment on not opening multiple threads on the same topic.
    I am new in this form and this is my second thread, and the first had nothing to do with this topic.
    Can someone explain his comment to me? Did I do something wrong?
     
  10. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
  11. Belteshazzar

    Thread Starter Member

    Mar 16, 2010
    34
    0
    I have something in mind maybe you guys can give me some input.

    I built the attached inverter circuit a while back using a LM555. It works well for very low power.

    I used a 28/115 Trans and got about around 24VAC. Voltage drops though, under load.
    Seems to have very low power.

    How about using the same principle design to get the 60hz oscillation but feed the main circuit 48VDC and use transistors accordingly?

    I would use a VReg to isolate the high voltage and give the 555 the correct voltage lower voltage but still drive the main transistors with 48VDC.

    The transistors would take the 60hz oscillation through the base and give me my AC output.

    The conversion to AC cuts the voltage to about half...so 24VAC. Don't need stepup or stepdown transformers.

    Technically, the attached circuit is a tranformerless circuit taking 12VDC to 6VAC.....what you would do with 6VAC I don't know, but just stating the fact to perhaps to built upon this circuit principle.

    The problem is I don't know my calculations for the transistors, saturation etc to have the trans take the 48VDC.
    Maybe 2 sets of Trans driving each other or mosfets? darlington? ...IRF series?

    Any thoughts?
    I really appreciate it!
     
  12. Belteshazzar

    Thread Starter Member

    Mar 16, 2010
    34
    0
    Oh, That one is one in the same....that thread is also my identical thread.

    I must have made a mistake and doubled it.

    I think I know what mistake I made, I check on "polls" by accident and tried to get out, but lost the page.
    So I redid the thread because I though it never went through because i did not press "submit thread"

    I apologize....my bad
     
  13. Belteshazzar

    Thread Starter Member

    Mar 16, 2010
    34
    0
    Ok...no transformerless in sight,

    I found the attached schematic for a low power inverter using a center tapped transformer.

    Does anyone know the calculation for the correct center tapped transformer windings and wattage to produce 24VAC at max 1 Amp from 12VDC as per the circuit?

    The transformer is driven by the two darlington transistors push-pull fashion.

    The original circuit calls for a 120V/18V center tapped that is connected backward to obtain 115VAC

    What would I need with this circuit for 24VAC?

    Thanks, I appreciate the help!
     
  14. kubeek

    AAC Fanatic!

    Sep 20, 2005
    4,670
    804
    You could use a simpler step-down converter, which uses just one inductor instead of a transformer. Personally I would try to find some ready chip, like the LT series, these should be pretty sure to work right on the first try.
     
  15. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    As mentioned before, this is a 24VPP, not 24VAC. It would be a 12VAC, and that with a square wave. You would loose several volts just in the transistors.

    Then there is the fact a 555 drops around 1.2V on the Vcc side on the output, further reducing the voltage. A CMOS 555 might work better.

    For a 24VAC square wave you need 48V. For a 24VAC sine wave you need 68 volts DC.

    There are reasons transfomers are so popular.

    It could be done with a simple booster to create 48V from 12V. I've also designed 555 oscillators to work using more voltage than their maximum power supply voltage.

    [​IMG]
     
    Last edited: Apr 3, 2010
  16. Belteshazzar

    Thread Starter Member

    Mar 16, 2010
    34
    0
    Great, thanks I want to build this circuit on a breadboard.

    I have almost all comp. just need to order the ZR's and Q's

    What are the transistors Q1-Q4?

    Question...specs on my LM555/NE555 from Fairchild alows max 16V at Vcc.

    I just want to confirm, as per your schematic, 30V going through a 20V zener will put how much voltage to pin 8 & 4?
    20V or actually less?
     
Loading...