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Diode help

Discussion in 'General Electronics Discussion' started by BShelton, Aug 20, 2012.

  1. BShelton

    BShelton

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    Aug 20, 2012
    Brand new to the forum so I may be shabby on etiquette.
    I'm looking for an axil lead type diode to use in a power cable that "Y's" from a camera to two 24 volt batteries.
    I've been told that this is necessary to prevent voltage from going from the battery with more voltage to the battery with less. The reason I need the "axil lead" is because I want to fit the diode inside the 3 pin XLR connector.
    The amperage draw will never be more than
    10 amps surge at start up.
    Have I provided enough information?
    Thanx for any responses.
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Almost :)

    How long is the startup surge, and what is the normal current requirement?

    I presume you're powering it from 2 batteries? Yes, a diode in each lead will stop one battery from trying to charge the other one. It will also save your camera from a potentially expensive fix if you accidentally connect a battery up backward.

    10A -- that must be some huge camera!
     
  3. Electrobrains

    Electrobrains

    259
    5
    Jan 2, 2012
    I suppose the surge current is less of a problem. More important (as Steve asks you about) is the continuous current. That will generate heat when the diodes are squeezed into a tight place.
    If it's less than approx. 0.8A you could probably use a couple of cheap standard diodes like 1N4001, 1N4004, 1N4007.
    If it's between 1 and 2.5A I would suggest a schottky diode like 1N5821 or MBR340G
    Just put the cathodes together (the side with the ring) and connect that side to the load.
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Yeah, most rectifier diodes allow a fairly massive overload for one mains half cycle (that's around 0.01 seconds).

    If your surge is approximately this long, there will generally be no problems. If it's 1 second, or 10 seconds and/or it is repeated, then you'll have to think about a component that is significantly higher rated [edit:than one suited for the continuous current].
     
  5. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    All good advice here. Here are a few specific pointers.

    All diodes drop SOME voltage. Standard diodes will drop about 0.8V or a bit more, depending on the current flowing through them. This means your 24V battery will be 23V at the camera.

    Schottky diodes drop about half as much voltage and might be a better choice.

    Small diodes around 2 mm diameter are rated for around 1A continuous. Larger diodes around 1/4" diameter are rated for around 3A continuous. Both types can tolerate short surges of at least ten times the continuous rating.

    Diodes also have a maximum allowable reverse voltage (reverse breakdown voltage) rating. In your application, 40V reverse voltage should be plenty.

    1A silicon diodes: 1N4001 (1N400x series)
    3A silicon diodes: 1N5401 (1N540x series)
    1A Schottky diodes: 1N5819/MBR140P
    3A Schottky diodes: MBR340
    Diodes with higher current ratings are available but they're big and they're not usually in axial packages.

    Go to digikey.com and search for "diode", go to "discrete diodes" page, and narrow down your search.

    For reverse voltage, choose 40 to 100V. For current, choose the current you need and a few options above that. For mounting type, eliminate surface mount. Choose standard or Schottky. Good luck!
     
  6. BShelton

    BShelton

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    0
    Aug 20, 2012
    So here is more info on what I seek.
    The electronics guy at the rental house told me that he uses a Schottky Diode # Y 1545 DN (45 V, 15 A) for this "Y" cable. The problem is that he uses a junction box to connect the cables and that gives him plenty of room use the schottky diode in the 220 package. But this package is way to big to put into a three pin XLR connector and that is why I am in search of an axil diode. Does such a thing exist that can do what the Y 1545 DN can do?
    Thanx for any replys.
    Cheers
     
  7. Electrobrains

    Electrobrains

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    Jan 2, 2012
    You must tell us the continuous current, otherwise we cannot answer...
     
  8. CocaCola

    CocaCola

    3,635
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    Apr 7, 2012
    An axial diode of similar rating is going to be about 8-10mm in diameter, no smaller than a TO-220 in the end...

    http://www.ebay.com/itm/10PCS-15A-4...875?pt=LH_DefaultDomain_2&hash=item3a78d9f7f3
     
  9. BShelton

    BShelton

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    Aug 20, 2012
    The continuous amperage is less than 5 amps at 24 volts. The startup peak would probably be no more than 8 amps.
     
  10. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    And how long does the startup peak last?

    It sounds like you're guessing. Have you measured any of this?
     
  11. Electrobrains

    Electrobrains

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    Jan 2, 2012
    Then you could probably use a VS-12CWQ03FNTRPBF if you have approx. 6.5mm space. It contains two diodes.

    If that one is too big, you could look at this one: PDS1040L. It's amazingly small, but would run at the limit in your application.

    In any case, I strongly suggest you solder whatever diode to some metal part within the connector, or it may overheat!
     
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