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basic general question

Discussion in 'Electronic Basics' started by [email protected], Mar 19, 2007.

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  1. Guest

    Hi,
    Im a total noob to this field and was wondering if anyone could
    provide input to prevent me from blowing up my ac output.
    What im doing is charging a home made HV cap with the following.
    I have a 1 amp 12vdc adapter, which i will be connection to a 12v
    1amp neon sign power supply. output is 2kv ac @ 10ma. I will be
    rectifing & doubling voltage to charge the cap however i was wondering
    if this AC type conerter could possible draw too much current to burn
    it out?
    I have found other similar circuits however only reference to a
    resistor or charging resistor was after the diode to prevent feedback
    on discharge of the cap. Im not entirely sure if this was to limit
    current charging as well as it wasnt clearly explained. I thought this
    would be the best place to ask before try. I was thinking of adding a
    1 or 2amp fuse between the ac adapter and neon supply to prevent
    killing the adaptor however this wont limit charging current if i need
    to. For my charging resistors i really dont know what i should put in
    as i dont want to drop below the 10ma current if possible and also
    dont want to drop voltage either if i can get away with it.
    Any recomendations would be greatly appreciated.

    for those that are curious this cap is for a pulsed hv lazor
    experiment

    Thanks,
    Caltus
     
  2. First, this will kill you no problem.

    How will you convert DC to AC?

    Last, this will kill you no problem.
     
  3. Your point? A gun will kill him too if he points it at his head(first he
    will need to make sure it is loaded).

    Breakdown of air is about 30kV/cm so its not like this thing will jump out
    at him. Obviously if he's storing charge on the cap then he will need a safe
    way to discharge it before sticking his hands in there.

    http://engr.nmsu.edu/~etti/3_3/3_3h.html

    In any case 10mA isn't, in general, enough to kill.

    You would have been more helpful to try to answer his questions instead of
    stating the obvious.
     
  4. John Fields

    John Fields Guest

    ---
    I notice that even though you were critical about Homer's not
    answering the OP's questions, neither did you. Is there a reason for
    that?

    Also, you obviously aren't familiar with the obvious if you think
    that a cap charged up to 4kV won't supply more than 10mA into a
    human load.
     
  5. Most people know a gun will kill them. Not as many know a sign transformer
    will do this as well.

    The fact that he's confused about what a transformer will transform is a red
    flag that he is in the unknowing group.
    You wanna take a chance on that?
    I asked him a basic question and I warned him of the danger. You'd have done
    better to mind your own business since your knowledge is so slim.
     

  6. Oh!! Great come back. You asked him a question... did he ask for a question
    to his question or to answer his question? If you know so much about this
    shit then surely you could supply more information. Your question about how
    he will convert DC to AC shows just how ignorant you are... Your trying to
    act like your intelligent by misdirection. The crux of the matter is not
    that how he will get AC from DC(which I assume he will do by an inverter
    like everyone else) EXACTLY what he asked.

    Unlike you I do not know the true answer so I did not respond. I wouldn't
    want to give him bad advice. Maybe you should take that advice instead of
    trying to act like you know something about something you don't.

    My answer would be to add about 100kohms in series with the cap to generate
    a peak instantaneous current of V/R ~= 2k/100k A = 1/50 A. While this is
    over is rated max of 10mA it is only 10mA above it and will die down to 7%
    of that within ~5 RC's. For his application this might be to long. He
    mentions that it is for a pulsed laser but how long between each pulse does
    he need. How big is the cap? In anycase he could work down from the 100kOhm
    resistor to increase the charge rate. Although having a resistor of 1ohm
    produces an instantaneous peak current in the secondary of about 2000 A and
    that means its over 4M in the primary. I'm sure that he will definitely not
    get this out. But even if it pulls just 10 amps from the 12VDC supply it
    could eventually cause problems. (depending on how fast and how many times
    it is pulsed) Obviously there will be a saturation point that will limit the
    peak inverse current and most devices can handle a substantially higher peak
    inverse current but I have no specific answers.

    But unlike you have I have no practical experience with the subject so I did
    not answer... You also obviously have no practical experience but answered
    with nonsensical questions trying to act like you know something that you
    don't(which you do a lot of).

    I mean, come up... WTF is up with "How will you convert DC to AC?"??? WTF do
    you think you can ask such stupid questions. You are assuming the guy is a
    total idiot... and this really means you are the idiot. He did not ask
    anything about that and you should assume that he as a little bit of a clue
    what he is doing. Now maybe it is the case he will hook up the 12VDC supply
    directly to the sign transformer and it won't work... GUESS THE **** WHAT???
    YOU KNOW THEY MAKE 12VAC POWER SUPPLIES TOO? Your fucking question is moot
    and just a waste of time. If he does have that problem he will post back and
    say it doesn't work and then someone will solve that problem very quickly
    and he will just have to run to wal-mart and by a 12VAC adapter or tear out
    the rectification in his 12VDC adaptor.

    Now instead of that bs you should have tried to answer his real problem but
    no, since you have no clue you misdirect like a magician. A magician has no
    real magical powers so they pretend. You are nothing but an intellectual
    magician. I see your BS all the time in this NG and you do more harm than
    good and I think its time someone pointed it out. Surely though there will
    be those that will jump on me because they too are intellectual magicians
    and everyone knows you guys stick together.

    Also, it is true its a probably a good idea to point out that it could kill
    him but if he doesn't know this already then maybe natural selection needs
    to take place. Also, every time someone plugs in a device you need to warn
    them they might die too. Do you know that only about 200 people a year die
    from electrocution? Of those how many do you think are not electricians or
    kids?

    "A low-voltage (110 to 220v) 60 Hz AC traveling throughout the chest for a
    fraction of a second may induce ventricular fibrillation at currents as low
    as 60 to 100 mA; about 300 to 500 mA of DC are required. If the current has
    a direct pathway to the heart (e.g., via a cardiac catheter or pacemaker
    electrodes), much lower currents (>1 mA, AC or DC) can produce fibrillation.
    Body resistance (measured in ohms/sq. cm)* is concentrated primarily in the
    skin and varies directly with the skin's condition. Dry, well-keratinized,
    intact skin has an average resistance of 20,000 to 30,000 ohms/sq. cm,
    whereas the resistance of moist thin skin is about 500 ohms/sq. cm. "

    So assuming the length of is arms to chest is ~30cm gives about
    2000/(30*30k) = 2mA. Ofcourse if he's playing with the shit wet or swetting
    a lot then that goes up to about 133mA.

    Instead of being a moron about the dangers you should just point out that
    its not safe and maybe link to a site about the dangers and some saftey
    precautions. Ofcourse if he's poking around in the circuitry while its life
    then maybe he deserves to get electrocuted. Its not that bad though, I've
    messed around inside of life TV's and not be electrocuted. (Maybe it was a
    stupid thing to do but I'm alive.)

    The point is, Homer, is that if your not going to try and answer is
    questions then why bother to post? I know you need to feel useful but its
    just a waste. Try volunteering at something your good at like picking up
    trash.
     

  7. This was just for a rough approximation. Obviously its an RLC circuit but
    this should just result in reducing the overall peak instantaneous current
    which means RC will effectively be larger. I did most of those calculations
    earlier so they may be wrong. (My memory isn't so good these days). In any
    case it wasn't suppose to be a detailed analysis but just an overall general
    idea. The point is that increasing R increases the charge time but
    decreases the maximum instantaneous current. I would imagine that its not so
    important because it will be limited by the transformers and as long as the
    average current isn't to high over the charge time then it shouldn't be a
    problem but the average will need to include the number of charges per
    second too.

    I would think that if you just use it intermittently then you probably don't
    need a resistor. If this is pulsed many times a second then you'll need a
    more detailed analysis. (or just experiment) (also I'm assuming V = 2kVDC
    but since its suppose to be 2kVAC the above numbers will be off)

    In any case I'm not really trying to give any info because I have not done
    this sorta stuff before and I coudl be wrong. There are many web sites that
    talk about HV and stuff and you'll find more practical experience there.
    Also, an important side note, which you probably know, is that the capacitor
    will probably be the most dangerous thing there. You should make sure you
    safely discharge the cap if you plan on messing around it. The 2000V could
    span a mm or so and get you. Probably won't kill you but could hurt.

    If your eager to start you might try using a 1M resistor and taking some
    measurements such as charge time(which you can approximately compute
    anyways) and run it for a while and see if things get hot(very doubful).
    Then work your way down from there until you reach your specs. My guess,
    and its only a guess, that you could probably deal with maybe even just a
    few hundred ohms or even less and everything will work fine if your not
    pulsing it hundreds of thousands of times a sec.

    You might want to give more information on the specifics so someone that
    knows about this stuff can give a more informed decision. (although maybe
    all pulsed lasers follow a specific implementation). I think the two
    important things are the capacitatance, pulses per second, and operation
    time.

    Jon
     
  8. You're still an idiot. Hooking up a 12 VDC supply to a sign transformer
    isn't going to do much of anything. Asking questions is the best teaching
    method.

    And your assumptions could kill him. I've been working with electronics and
    electricity for over 50 years and I don't fool with sign transformers or the
    like without following a lot of precautions. For someone with as little
    knowledge as he shows his next few steps could end his world.
     
  9. Guest

    ok, I appreciate all your concerns for safety and believe me all
    precautions will be taken.
    the cap size will certianly be more than 100 times more powerful
    enought to kill myself but i will be doing whatever so that wont
    happen. So lets not worry about that for now .
    the basic charge curcuit after ac adapter and fuse is as follows
    the ac current to charge the cap will be 1/2 wave rectified on + and
    1/2 wave on - using 4 6kv 200ma diodes.
    each ac lead will have 2 diodes connected to it ( forward and reverse
    on each)
    the the 2 + ends will be positive out and the 2 negative ends will
    be negative out. this will evenly split the ac into a 1/2 wave
    rectified positive and 1/2 wave rectified negative. 2kv ac usually
    means peak + and - is 2kv so by seperating them i will have
    effective 4kv diference on leads for cap charging without
    multiplying.
    now this is where i have questions. 1) imaging this is going
    straight to a large cap. will discharging the cap cause feedback to
    the 2kv transformer? I have seen others use a 1k ohm resistor past
    the diodes for feedback prevention when the cap is discharged? I know
    that resisters for this could vary and ohms law dictates that if i
    use large enough Resistors most the current and voltage will go thru
    however if a return spike came back on discharge it would filter and
    prevent most or some from hurting my diodes or transformer. Thing is i
    would like to prevent as much feedback as possible however do not
    want to drop as much voltage. My experience comes form Whimhurst
    machines and variants so i dont know alot about HV resistors. Im
    stepping up from those as my projects need more current that
    vandegraff. and believe me when it comes to safty, with leyden jars
    theese can be just as dangerous or more so.


    i would also prefer to sync charging ( or at least discharging ) as +
    and - are perfectly out of phase on diferent leads.
    can i achieve this by charging first to a 3 way cap ( think of
    leyden jar setup with ground connection each on like how some
    whimhurst machines are configured, positive - ground chain -
    negative ) the discharging from them automatically?
    this circuit would be the same as a Greinacher voltage doubler

    thanks, any thoughts or jokes about the guy that will blow himself up
    is appreciated ;)
    lol
    Thanks,

    Caltus
     
  10. Obviously you don't know how to fucking read.
    omg! you must be fucking l33t all those years of installing ceiling fans and
    you call yourself an expert. I guess you really think that just because
    you've been around for 50+ years means your an expert. To bad you don't
    understand that age != experience. Ofcourse one might think it is correlated
    but usually arrogance and ego wins out every time.
     
  11. Guest

    thanks Jon, that is exactly what i was looking for. you have
    answered while i was typing that last post it appears.
     
  12. Yeah, I agree. If your stupid enough not to be careful then your stupid
    enough to die. (Ofcourse there are always accidents but if one is
    irrational like homer then they will never get anything done. Sometimes you
    gotta take a risk to make progress)
    Yes, there is things such as inductive kick bad, EMF radiation, etc that can
    cause problems. I cannot really tell you much because I do not know either.
    There are several sites I have seen that do discuss this topic though. What
    you want is some type of path to ground that the feedback can take.

    For example, metal oxide varistors are used when a voltage spike on the
    mains is larger than a certain amount and the mov sorta opens up and proves
    a least resistive path to ground. This prevents that spike from going
    through the transformer. You could use somethinglike that but not sure if
    they make them for that high of a voltage. (although maybe you could use
    several in series) Theres probably a better method and ofcourse theres a
    whole industry built around HV stuff and they all have these very special
    techniques and exotic devices for dealing with these kinds of issues. You
    might look into how they handle this stuff in power distribution. (usually
    though its for high currents but maybe something will work).

    I would say maybe you could just ignore it for now and see but you might not
    want to take the chance and ruin your components.

    Maybe you can put a relay switch between the cap and diodes to completely
    remove it from the circuit? The relay can be triggered to open when the cap
    has reached a certain voltage. Might be a good solution. Ofcourse when it
    closed there would be an inrush of current and this could effect the
    contacts.
    So you want to charge up one side while discharging the other? (so you would
    increase the pulse rate by a factor of 2)
    No, I have no issues with you doing this. Its better than sitting on your
    hands or twiddling your thumbs cause your too afraid. There are a lot of
    weenies out there. If it wasn't for people taking risk we wouldn't be where
    we are. Ofcourse its not that big a risk and you seem like you know the
    risks. There are many things you can do such as wearing insulated gloves or
    even a suit but this isn't really necessary if you just pay attention(which
    I think you will and its not really my place(or anyones) to tell you what
    you can and can't do)

    Have fun.

    Jon
     
  13. John Fields

    John Fields Guest

    ---
    Yes, nice post.

    What we need to know in order to go forward is the value of the OP's
    homemade capacitor, the output frequency of the neon PSU, and the
    discharge time of the cap through the laser. From that we can tell
    him what the charging impedance must not fall below in order to keep
    from damaging his wall-wart and what his pulse repetition rate must
    not exceed in order to get maximum power out of the laser.
     
  14. John Fields

    John Fields Guest

     
  15. Yet I do it so much better than you.
    Think entire building climate control systems of the most complex kind, not
    to mention all sorts of industrial experience, some with very unusual
    equipment.
    It does.
    Actually that's exactly what it means.
    No, being able to fix equipment and systems that others have tried and
    failed to service is more than enough proof. Passing the electrical exams
    with the highest numbers of anyone is just a bonus. And of course I can also
    write grammatical English.

    I gave the OP good advice and tried to start helping him. You came in and
    pissed all over the reply with your bone headed comments.
     
  16. Do. Use one hand only and stand on an insulated surface - even a stack of
    dry newspaper will do in a pinch. Try to use well insulated tools and think
    the thing you are going to do through.
     
  17. Guest

    i think ill do the throw switch like you suggested to prevent that
    feed back. Im going to making my own relay switches to insure
    proper insulated and safely encased . basically all my work will be
    contained in pexiglass with a few redundant grounding options in
    case a path burns out.


    this is not really necessary for the lazor project. Im looking however
    for a simple solution to to sync the negative and positive pulse that
    i split from the same output. the negative ac phase must match the
    exact positive phase.
    End result i want for this seperate project is pulsed dc that is equal
    and opposite + & -. this is for hv tests regarding field polarization
    effects. Non phase is usless for this test as the oppsite current
    is gone or stored before the other pulse comes out. That why i was
    thinking on using the doubler using the ground . just not sure on a
    circuit that will pulse out from that . that curcuit " i think"
    just maintains HV voltage if we dont use too much load where i want
    pulses like discharges instead.
    I thinking my best option might be to wrap my own transformer with 2
    equal output windings. for the sync, any better suggestions? If i
    wrap one winding in one direction and the next in the opposite
    direction would each output winding be opposite polarity in sync? im
    not 100 % sure tho i think thats how it works. of course if this works
    i woudl run it on a figure 8 laminated core with input on centre
    and oppsite outs on either end to prevent it from shorting across
    the increased diference. in voltage. how does that sound?
    Again thanks for all your input.

    Caltus :)
     
  18. Guest

    here is the transformer i bought and i have 2 of them.

    http://www.allelectronics.com/cgi-bin/item/HVS-1/480/GAS_TUBE_SIGN_POWER_SUPPLY_.html
    Specifications: Input: 12 Vdc @ 1 Amp (Suggested power source CAT#
    DCTX-1215). Output: 2,000 Vac @ 10 mA. Open circuit voltage: 3,000 Vac
    30Khz. Short circuit current: 15 mA. UL.

    I got the recomemded 1.5 amp power supply however other findings
    show that is a bit much current for this devic and i got another
    adapter that outputs 1 amp , again i dont want to burn anything
    out.
    i got an asortment of resistors and diodes as i was not sure what to
    get.
    6 x 220 ohm 3 wat , 3 x 1k ohm 5 wat.
    10 x .2 amp 6k diodes and a wackload lower voltage ones that prob
    will not ever need now

    as for the home made cap i made from 6mil polyethelene which someone
    else used, surface area for diferent caps for now are ony small for
    testing now and will get bigger later. ( dangerous either way im
    sure )
    foil surface area is about 30 cm x 5 cm for each pos and negative
    plate and tightly rolled around a dowel.

    other caps are same materials but smaller surface area . later for
    good discharges i may have to go 10 or 50 times the size as the one i
    mentioned. i dont expect you to do all the math as im lazy however
    just want you to have a better idea what i have to start with other
    then loads of pexiglass
     
  19. John Fields

    John Fields Guest

    ---
    You're a liar.

    All _you_ tried to do was to piss all over the OP in a
    self-aggrandizing effort without offering anything other than
    pejorative comments.

    You obviously don't even have the capacity to envision the system he
    was describing (as evidenced from your retort about 12V into the
    primary of a transformer, when the OP clearly stated that the
    _supply_ was 12VDC in and 2KVAC out) and yet you pretend to know
    what you're talking about?

    You're an utter disgrace to decent Canadians everywhere, eh?
     
  20. Lord Garth

    Lord Garth Guest

    Don't sweat the extra current capacity, the circuit will draw what it
    requires. If your voltage is regulated to the correct value but your
    circuit needs more than the available current, expect the voltage to
    sag. Otherwise, you're good to go.
     
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