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need help with flyback transformer

Discussion in 'Repairing Electronics' started by lev77, Feb 15, 2011.

  1. lev77

    lev77 New Member

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    can some one help me out here, i need to know if the is a rectifier in this transformer and if it is which ones are connections?
    thanks
     

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  2. DerStrom8

    DerStrom8 Super Moderator Most Helpful Member

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    Hi, lev77! Welcome to electro-tech!
    That style of flyback transformer usually has a rectifier already in series with the output. It is often moulded into the case, so the connections have already been made, and it is difficult to remove the diode.
    Der Strom
     
    Last edited: Feb 15, 2011
  3. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Yes, the EHT rectifier is potted inside the transformer.
     
  4. dave

    Dave New Member

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  5. lev77

    lev77 New Member

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    Thanks guys for ur replys. So i cant use just rectifier from this sistem. Is there any rectifier in tvs that i can use?if not wich recrifier i can use that as good as that one.
    Thanks
     
  6. DerStrom8

    DerStrom8 Super Moderator Most Helpful Member

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    There aren't very often rectifiers in tvs that are rated for that kind of voltage. However, old-style (not solid-state) microwave ovens have a high-voltage (10-15kV) diode that makes up part of the voltage doubler circuit (between the transformer and the capacitor). Old microwaves are fairly easy to find, but if you decide to go this route, I wanted to make sure you know to be VERY careful around the capacitor. They can store lethal charges for extended periods of time. I once opened up an old microwave that hadn't been used for years, and when I shorted the capacitor I still got a pretty big spark. I'm glad I was using wire and not my finger! :D
    Anyway, this may be the kind of diode you're looking for.
    Good luck!
    Der Strom

    P.S. What kind of voltage and current are you looking to rectify?
     
    Last edited: Feb 15, 2011
  7. lev77

    lev77 New Member

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    thanks storm ill have a look. what dos it look like? i dont know much baut this stuf.
    what im trying to do is connect car ignition coil to HV capacitor 30kv.. one on pic.
    i been told i need a rectifier thats in flyback transformer.
    is there rectifier that big that i can just go to shop and buy one.. if it is how big dos it have to be.
    thanks
     

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  8. tunedwolf

    tunedwolf Well-Known Member

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    I'm already scared...so do you want to go in a bin bag or an urn?
     
  9. DerStrom8

    DerStrom8 Super Moderator Most Helpful Member

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    Now, now, tundedwolf. It sounds to me like Lev77 is simply trying to make a tesla coil or something. As long as he knows to be careful, I think he'll be fine ;)
     
  10. DerStrom8

    DerStrom8 Super Moderator Most Helpful Member

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    30kV is rather high for a single microwave oven diode. You may be able to find a few of them and connect them in series, with some high-value resistors in parallel to help to distribute the voltage, like this:
    HV_diodes_in_series.png
    Here's what a microwave diode looks like:
    [​IMG]
     
    Last edited: Feb 16, 2011
  11. lev77

    lev77 New Member

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    tunedwolf im not ready for a big bag but some big fireworks :D:D:D
     
  12. lev77

    lev77 New Member

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    DerStrom ill get as much diodes as i can but u have to help me out with high-value resistors which ones to get.
    thanks
     
  13. DerStrom8

    DerStrom8 Super Moderator Most Helpful Member

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    I believe the resistors should be around 1Meg, but of this I am not exactly sure. Perhaps someone else can help here? The wattage will depend on the amount of current your ignition coil is drawing/producing.
     
  14. lev77

    lev77 New Member

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    derstrom i got the diodes. which ones can i use and which high-value resistors do i need to get
    thanks,,,,,
     

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  15. DerStrom8

    DerStrom8 Super Moderator Most Helpful Member

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    1 megohm, 1-watt resistors should work, but again, it depends on the amount of current from the ignition coil. You may have to go for 5-watt resistors. What are you using for the driver circuit?
     
  16. unclejed613

    unclejed613 Well-Known Member

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    so you intend to charge up the cap and make a big kaboom when you discharge it?

    Wile E Coyote is drooling....
     
  17. lev77

    lev77 New Member

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    schematic of driving the ignition coil

    this is what im useing to drive coil....
     

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  18. DerStrom8

    DerStrom8 Super Moderator Most Helpful Member

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    Wow--I've never seen a driver circuit like That before! Maybe you want to try a simpler circuit like this one:
    [​IMG]
    It's much easier to build, and you can change the voltage and current of the output by using different-value capacitors.
     
  19. unclejed613

    unclejed613 Well-Known Member

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    ok, he's using a capacitive discharge unit to drive the coil. a simpler means would be a 12V relay wired as a buzzer, and the other set of contacts acting as an interrupter like the points in a car ignition.... derstrom? are you bucking for a Wile E as well? a 120V dimmer and line voltage? guaranteed to let the smoke out somewhere.....

    lev77 what do you intend to do once you get that cap charged up? do you realize the carge on that cap will be lethal far beyond the charge on a microwave oven cap? i just want to find out how much you've thought this "project" out. "fireworks" is a bit vague. high voltage spikes from an ignition coil can be painful if you get bit by it, but high voltage stored by a large capacitor is much more dangerous (imagine one long continuous "spike" that continues to discharge through your body long after you're dead)..... i just want to know that you've considered the dangers here and take appropriate measures to keep out of harm's way... 30kV can "reach out and touch you".... i work at a shop that services microwave ovens that have similar caps charged to 5kV, and one tech literally got killed instantly trying to discharge the cap with a screwdriver......
     
    Last edited: Mar 5, 2011
  20. DerStrom8

    DerStrom8 Super Moderator Most Helpful Member

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    Hi, unclejed613!
    I have used this circuit before do drive an ignition coil, and the coil handles the line voltage fine. The capacitor is very important, though. It is there to limit the current so that no real damage can be caused (either inside or outside of the ignition coil). I would recommend using no more than 1uF of capacitance, though, or else the coil might heat up.
    In car ignition coils, since the primary and secondary coils have a high mutual inductance, you generally get a voltage spike of a couple hundred volts on the primary, anyway. The coils are designed to withstand this kind of voltage, so 120-240 volts from mains is not likely to cause much, if any, damage.

    You are absolutely right, though, about the dangers of charging a high-voltage capacitor. lev77, you MUST BE EXTREMELY CAREFUL. Again, I can't stress this enough.
    Best of luck,
    Der Strom
     
    Last edited: Mar 5, 2011
  21. unclejed613

    unclejed613 Well-Known Member

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    i used to run ignition coils from a 12V transformer, a variable one like a toy train transformer. and i used CRT anode wire for the secondary wiring. never tried what he's trying though..... got bit from CRT anodes (quite a bit less capacitance than what he's playing with) enough to know better....
     

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