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9v dc to 9v ac conversion

Discussion in 'General Electronics Discussion' started by IBS, Nov 11, 2012.

  1. IBS

    IBS

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    Nov 11, 2012
    I'm new to this forum, so please be patient with me...


    I have a 9v ac multi-led controller (flashes multi-colored led's in various sequences). The controller is dependant on AC for timing. I am not concerned so much with the actual frequency of the timer as long as it is reasonable (30 - 70hz), but for the sake of specifics let's say 60hz. I believe a square wave will will work, and I don't think it needs any filtering. The device operates on a 9vac 250ma wall converter, but I would like to make it portable. I will probably use 6 c-cell batteries for the input voltage. Can someone tell me how to build a converter to acomplish this? I am not an electronics geek, but I do understand basic electronics, can read (very) basic schematic diagrams, and can solder proficiently.

    BTW I have spent days on GOOGLE trying to figure this out, but no-one seems to really NEED 9vAC, so they just push DC through the bridge diodes.

    Thanks in advance.

    IBS
     
  2. duke37

    duke37

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    Jan 9, 2011
    I would think that an oscillator (4047?) driving an H-bridge would do the job but I have never used one.
     
  3. IBS

    IBS

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    Nov 11, 2012
    Thank you Duke. Your reply was about 3 feet above my head. I understand what an oscillator is, and what its basic function is, but don't have a clue what an H-bridge is.:confused:
    I am really looking for a basic diagram, with the exact components identified. I wouldn't have any idea what values to use for resistors, caps, etc...

    I do however appreciate your response, and look forward to future discussions.

    IBS
     
  4. IBS

    IBS

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    Nov 11, 2012
    To Future Reply-ers...
    My knowledge of electronics is as follows:
    I can Identify resistors,capacitors,chokes,transistors,IC's, diodes, and probably some other components if you pointed to them on a circuit board. I have some idea of what they do independantly, but do not know how they work together to make a circuit work, or what values would be required to perform a desired task. I admit I am just a wanna-be electronics tech, and will probably never be one. There are times however, That I need (want really badly) information / instruction on building some kind of device that could probably be purchased, but where's the fun in that?

    IBS
     
  5. Harald Kapp

    Harald Kapp Moderator Moderator

    9,306
    1,888
    Nov 17, 2011
    What is your power requirement (Watts)?

    A simple way of doing thos would be to build a 60 Hz oscillator, e.g. using a 555 IC. Here is a circuit and a calculator tool for this IC.

    Connect a series capacitor to the output. Connect a 1:2 transformer to the series capacitor, second pin of the transformer goes to GND.

    Or look at this complete circuit. Only you'll have to adjust the transformer ratio for 9V output. The circuit itself should operate from 9V without modification.

    What controller ist it you're using? I wonder why it relies on the AC input for timing.

    Harald
     
  6. IBS

    IBS

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    Nov 11, 2012
    Harald;
    9v @ 250ma. That's what the PS was rated.
    The circuit is from a rotating LED display base used for displaying crystal objects (laser cut glass artwork etc..) The LED's are different colors, and they turn on and off in various patterns / sequences. I think the AC current is required for the sequence timing. I have tried to apply DC to it but the LED's flash once, and dont come on again. I see on the circuit board, there is a bridge rectifier, but some of the circuitry branches before the bridge. I don't know what part of the circuit uses the DC. I do know that the motor requires AC (it says so on the label), but I'm not using the motor for this project. All I know for sure is that if I hook up 9vAC the lights flash like they are supposed to, and with 9vDC they don't. This would not be a problem if I weren't trying to make this thing portable. I am going to make a wizards staff for next years holloween costume. I am going to embedd batteries, a switch, and the light controller inside the staff. The LED's will be inside a multi-fasceted crystal (2-3 inches diameter) on the top of the staff.
    I know it's rather trivial, but I still would like to do it.

    IBS
     
  7. Harald Kapp

    Harald Kapp Moderator Moderator

    9,306
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    Nov 17, 2011
    Since you have opened the box anyway, why not go two routes:

    1) Use 9 V DC (before the bridge rectifier) to supply power to the circuit without losses due to transformers or similar.
    2) Open the connection from before the bridge rectifier to the rest of the circuit. If it is for timing only, it should be only one wire and will not require much power. Use a 555 based timer to apply a 50 - 60 Hz signal to this connection. You may need to put a capacitor in series with the output of the 555 so timing circuit sees AC only.

    You could also use just a single color changing LED.

    Harald
     
  8. cjdelphi

    cjdelphi

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    Oct 26, 2011
    you said you saw a DC rectifier... then the AC is being converted to DC.

    Bypass the DC rectifier and connect the DC supply up to where it has to go... - pictures of the circuit would give a better understanding.
     
  9. donkey

    donkey

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    Feb 26, 2011
    cj if he connects DC straight up to the rectifier it won't harm it will it? I don't see why bypassing the rectifier will matter except for maybe a little drop in voltage
     
  10. cjdelphi

    cjdelphi

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    Oct 26, 2011
    Because the person said that when 9vdc was connected, the light came on and did nothing, I'm half wondering if that's because of the voltage drop? if you supplied say 10vdc (via the AC/DC rectifier) would the circuit come to life? if so, i'd bypass the DC rectifier.
     
  11. donkey

    donkey

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    Feb 26, 2011
    6 C cells should be providing closer to 10volts on a good charge not 9 if my very inaccurate calculations are right.
    so I don't think its volts or current but as he stated there is something that branches of before the rectifier. I am at a loss as to what but its kinda interesting me
     
  12. cjdelphi

    cjdelphi

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    Oct 26, 2011
    hence the picture... :)
     
  13. Harald Kapp

    Harald Kapp Moderator Moderator

    9,306
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    Nov 17, 2011
    That technique is not unknown. A tap before the rectifier decouples some AC which can be used to control the timing in the circuit. Some alarm clocks use(d) this to count the time. That was before the advent of inexpensive quartzes.

    Similarly this could be used by the LED controller to synchronize the PWM for controlling the brightness of the LEDs to the mains frequency, thus avoiding interference.


    Harald
     
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