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Capacitor charging

Discussion in 'General Electronics Discussion' started by Mark34, Sep 29, 2016.

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  1. 73's de Edd

    73's de Edd

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    Aug 21, 2015
    Ah-haaaa, now we have the further needed information . . . . this is related to a photoflash unit.
    With several concepts of operation faults being seen.
    Typical photo-flash power supply circuits have a special main storage electrolytic that exhibits a very-very low leakage, in order to hold its voltage level up for the longest possible time.
    Also the main power supply is feeding a voltage sample down to trigger on that power supply circuit automatically, if it denotes a decline of voltage level being available, below a certain specification.
    That design then makes a constant voltage available to supply your photoflash tube.
    Now in looking back to the right terminal board and now knowing that an SCR is being involved instead, I am still seeing a fault, in it's being able to activate a photoflash tube.

    With your photo flash tube not being shown in circuit, it's looking like you are wanting to connect the far ends of the photoflash between the charged capacitor and one end of the SCR with the other end of the SCR then going to the ground and possibly your thought of using the FULL . . . UN CURRENT LIMITED . . . twelve volts of the battery going through RED / ORANGE tact switch to then activate the gate of the SCR.
    Your thinking there might be that the flash will then work.
    BUT look closely at the center of that flash tube and see that there is a central wire usually with a conductive paint around it, and THAT wire needs several kilovolts of temporary voltage applied to it for the internal gas fill to then ionize and THEN the tube will be able to flash through that then conductive path with that high level of stored energy being in the main capacitor.

    Your present transformer that is used in the main power supply looks eerily similar to what we call a trigger transformer that is typically used to fire the flash tube but it's voltage source is a small paper capacitor that is chargeed up to the order of 200 V and then applied across the primary of that transformer with a resultant multi kilovolt coming out of the secondary of that trigger transformer to then fire the flash tube.
    Maybe "they " are thinking that they can repurpose the use of one of the trigger transformers for use as a power supply transformer, but I see the need of a more robust transformer for that main storage capacitors keep alive power supply application.
    Can you provide any on line reference to this " kit" so that we may then get into their minds and examine their "thinking" ?

    As per your very final comment on that diode, if this is an attention getting strobe.
    It could be that is a voltage sensitive semi conductor device that conducts at a certain voltage build up of the main storage capacitor threshold and then feeds down to the resistor below it and if that junction was connected to the SCR gate, it would cause the SCR to conduct.

    73's de Edd
     
    Last edited: Sep 30, 2016
  2. Mark34

    Mark34

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    Sep 23, 2016
    I sent you a private message 73's de Edd.
     
  3. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Mark, in amateur radio what you just did would be considered an echo. His name is Ed. "73's de Ed" means "Best regards (73's) from (de) Ed". So you're post should read "73's de Mark". ;) It was born when (Morse Code) ruled.

    Chris
     
    (*steve*) likes this.
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Arcane R Us
     
  5. davenn

    davenn Moderator

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    well if you want to go that way, then your ceramic us is totally pointless as it's capacitance value is going to be very limited for a start ... likely less than a few uF at most
    and is not going to hold charge for any signif time compared to an electrolytic

    consider you DONT have to be wary of "charged" ceramics lying around the workshop waiting to bite you cuz they don't hold a charge for any length of time,
    that's where electros win
     
  6. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    I think we're having a Struther Martin moment.
    It wasn't suggested to replace the 1000uf cap for operational use. The ceramic cap is only to test the PS using no load but a 10MΩ DVM. This way electrolytic leakage as the culprit can be eliminated.

    Doesn't matter though because I think Steve nailed the problem. Which seems to be a misunderstanding by Mark regarding what the voltage or capacitance rating of a Cap means.

    Chris
     
  7. Mark34

    Mark34

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    Sep 23, 2016
    Well i know what the voltage and capacitance of a Cap is but don't know about Cap electrolytic leakage, i did something else i removed the Cap entirely to see the inverter voltage it goes up to 30V and that's it.
     
  8. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Yes, old and understood by very few. That's it's charm!

    Chris
     
  9. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    If that was a scope measurement it would be meaningful. With a DVM?..... Eh, not so much!

    Chris
     
  10. BobK

    BobK

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    30V was the average. The inverter most likely produces short high voltage pulses, which might very well average to 30V.

    Bob
     
  11. Mark34

    Mark34

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    Sep 23, 2016
    Capacitor electrolytic leakage- discharge of current between Cap plates when charged but with no load, that's not too hard to understand.
     
    Last edited: Oct 1, 2016
  12. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    What? that statement doesn't make sense. (how can you have discharge without charge???)
     
    davenn likes this.
  13. Mark34

    Mark34

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    Sep 23, 2016
    Last message edited, is that correct?
     
  14. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    That's better, but remember that leakage exists even when there is a load. In fact it's a load all by itself. In many cases it can be considered to be a resistor in parallel with the capacitor.
     
  15. Mark34

    Mark34

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    Sep 23, 2016
    What capacitance/voltage should have the ceramic Cap for the test ? I could try another electrolytic Cap a 330V 160uF until i get the ceramic one.
     
  16. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    I wouldn't bother. It's clear that the device tops out at 250V. We can tell that because you bought it and that was the rating of the capacitor.

    There's all sorts of stuff you could try. larger batteries (D cells instead of AA), a higher voltage (try adding one more cell), or even a voltage doubler on the output.

    All of these have their drawbacks, either by putting the circuit at risk of premature failure or reducing the speed/capacitance at the output.
     
  17. Mark34

    Mark34

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    Sep 23, 2016
    Maybe a transformer with a greater turns ratio?
     
  18. duke37

    duke37

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    To make a transformer with a greater turns ratio, you could add more turns on the outside of the transformer you have. The new winding should be in series with the existing secondary and connected in the correct phase. If you have an inductance meter, add turns to equal the inductance of the secondary.
    The rectifier should be upgraded to suit and any voltage limiting feedback should be left in place.

    The frequency will be very high and I expect that a 10nF capacitor will be big enough for testing.
    What is the input resistance of the voltmeter?
     
  19. Mark34

    Mark34

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    Sep 23, 2016
    Don't know the resistance of the voltmeter how do I find out ?
     
  20. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    When in the DC Voltage mode Standard DMM's have a 10MegΩ input resistance.

    Chris

    Edit: I had to cut 95% of this reply because it was intended for a totally different thread!:oops: So if anyone read it and struggled to make a connection to Mark's question,....there was none.
     
    Last edited: Oct 2, 2016
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