Voltage in a disposable camera capacitor!

Discussion in 'The Projects Forum' started by NM2008, Apr 14, 2008.

  1. NM2008

    Thread Starter Senior Member

    Feb 9, 2008
    135
    0
    Hi,
    Does anybody know off hand, what voltage a disposable camera flash capacitor would charge to?
    By looking at the circuit it is obviously high, but I do not want to risk putting the multi-meter on it, that split second could do damage!

    Thanks for your time!
    NM
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Yep, it can reach several thousand volts. You'd need a high voltage probe to read it. They're expensive.

    Be careful. You can kill yourself by creating a current path through your torso.
    When dealing with high voltage circuits, keep one hand in your back pocket.

    Here's a search for you:
    http://www.google.com/search?hl=en&q=Xenon+flash+voltage
     
  3. NM2008

    Thread Starter Senior Member

    Feb 9, 2008
    135
    0
    Yes, the circuit itself, gave me the impression that it could pack a nasty rap!

    Anyway, why I ask is, I am planning/thinking of building the strobe effect which the aviation industry use on planes, (navigation lights on wings, eg. 2 quick flashes left wing, delay, then two quick flashes right wing....)
    I have a strobe circuit built which replicates this effect, but it uses l.e.d's.
    Aviation strobes are expensive, so I though of using 2 disposable camera flashes and there high voltage circuits. But as they only operate on a single triple a 1.5v batery, the capacitor takes roughly 5 seconds to charge enough to make a visible flash, 5 seconds is too long for the cap to charge for the quick flashes!

    I was wondering which is best, trying to modify it, or should I build my own circuit with a cap that charges in about one second.

    THANKS
    NM
     
  4. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Well, AAA batteries have a pretty limited current supply. You might try using a "D" alkaline cell. That by itself may cause the circuit to overheat, though.

    You could try connecting several of the circuits in parallel to charge a single capacitor. But if any of the circuits failed shorted, you would have fun trying to figure out which died.

    Increasing the voltage supply by adding batteries in series would likely burn them out very quickly.

    Decreasing the size of the HV cap would reduce the charge time, along with the intensity of the flash.

    You could attempt building your own flyback converter supply. This page has a lot of good ideas:
    http://www.dos4ever.com/flyback/flyback.html
     
  5. Søren

    Senior Member

    Sep 2, 2006
    472
    28
    Hi,

    Time for a sanity check...

    It will charge to somewhere around 300V tops (+/- ~50V)which most DMM's will be able to measure.

    (I sure would love to watch "several thousand volts" going into one of 'em... As long as I can do so from a distance :D)
     
  6. Caveman

    Active Member

    Apr 15, 2008
    471
    0
    You are all right (to a point).

    There is a charger circuit that charges a cap to about 300V as Soeren says. This voltage is applied to the ends of the flash tube. However, 300V isn't enough to cause breakover (ie. flashing) in the flash tube. If the tube were about 1/4 shorter it would work, so a trigger transformer is added. This transformer takes a pulse from the 300V and steps it up to about 10,000V as SgtWookie says. This voltage is literally just connected to a piece of copper tape on the back of the flash tube about 1/4" from the ground side. When the 10,000V triggers, the gas between it and the ground side of the tube ionizes, effectively shortening the tube for the 300V across. The tube then breaks over and the 300V capacitor drops all of its charge into the tube causing a flash.
     
  7. Caveman

    Active Member

    Apr 15, 2008
    471
    0
    As far as quick flashing. The blocking oscillator boost circuit that is in these circuits is amazing and efficient. You could just merge a couple or more of these circuits side by side so that while one is flashing, the others are charging. Then just sequence flashes.
     
  8. Søren

    Senior Member

    Sep 2, 2006
    472
    28
    Hi,

    And since the question was... "Does anybody know off hand, what voltage a disposable camera flash capacitor would charge to?"
    This is the correct answer :D


    Well, since the question related to the cap, an answer of "several thousand volts" is absolutely wrong.

    Besides, the pulse from the trigger is nothing but... Just a very short decaying "ring", while the cap holds its (DC) potential for quite some time if unused.

    But thanks for the differentiation, The other guys in this tread obviously needed it ;)
     
  9. Caveman

    Active Member

    Apr 15, 2008
    471
    0
    A few years ago, one guy brought one in, and all the guys at the office looked at the schematic, and were baffled by the boost circuit. It actually depends on transformer saturation to work. I finally figured it out, but learned a bit about the rest of the circuit in the process.

    No work was done that week, but I pitted a few screwdrivers in the lab. :D
     
  10. NM2008

    Thread Starter Senior Member

    Feb 9, 2008
    135
    0
    Thanks for taking time to respond to my post,
    At least now I know what I am dealing with.

    Caveman, thanks for the info on the blocking oscillator boost circuit. I did not know about this.

    Soren, I am still in the early stages of electronics, I stated "off hand" as I just wanted to confirm if the cap, would be dangerous if accidentally touched while charged!

    Regards NM
     
  11. kubeek

    AAC Fanatic!

    Sep 20, 2005
    4,670
    804
    It is not too dangerous, but definitely an experience to remember.

    I once held the whole disposable camera flash circuit including battery and fully charged, by the edges, and it accidentaly slipped and touched my hand with all the pins on the bottom side. The jolt was really shocking and the hand (palm) was a bit paralized for few minutes. I was like ten years old, so that is how my first contact with high voltage looked like :)
     
  12. iONic

    AAC Fanatic!

    Nov 16, 2007
    1,420
    68
    Just try experimenting with the capacitor value.
    1) Will it fire with a 200V or even a 100V cap instead of the 300V
    2) Lowering the Cap value from 100uF to 22uF or even 10uF

    I believe you could get a less fearsome flash yet far brighter than an LED and with a much shorter charge rate between flashes!

    Interesting links:
     
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