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Help selecting the correct Diode

Discussion in 'General Electronics Discussion' started by Michael-J, May 14, 2016.

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  1. Michael-J

    Michael-J

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    May 14, 2016
    I need to supply 12 vdc (15vdc max) to a DC solenoid valve (1.7 amp continuous draw) from two separate source. I cannot have either source back feed the other so I think a diode in the output of each supply would work well to keep the sources isolated. I am not familiar with how to specify a diode and was looking for help in identifying the appropriate specs for the required diodes. This will be used in a piece of mobile equipment so there will be substantial vibration and temperature swings. The solenoid will not cycle more than once per second and continuous on time may be around 20-30 minutes at any time. I may also need to place the diode within a wiring harness but if not possible, could install in an enclosure. I am looking for heavy duty and reliable, cost is not a significant factor. Any ideas on commercially available connectors to incorporate the diode into a harness would be appreciated as well.
     
  2. Minder

    Minder

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    Apr 24, 2015
  3. Michael-J

    Michael-J

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    May 14, 2016
    Thanks for the diode recommendation. Should I be concerned about any voltage spikes from switching the solenoid on and off or will this diode handle that? I could splice it in-line and use heat shrink but am concerned about the durability. I was hoping someone was aware of some type of compact in-line enclosure to encase the diode and solder joint in to protect it. Not sure if this type of molded case would be an issue for heat dissipation? (or how much heat may be generated by this diode).
     
  4. Minder

    Minder

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    That is a 5 watt diode that should be rated well within the current you are using, You will probably find it barely gets warm.
    If you are concerned about vibration and durability I would rate a soldered splice high on the list, to say nothing of the neater approach.
    If worried about spikes, place a reverse biased one across the solenoid, which is recommended anyway
    You would need this in smaller qty's http://www.digikey.ca/product-detail/en/stmicroelectronics/STTH5L06RL/497-5231-1-ND/1121684
    M.
     
    Michael-J likes this.
  5. dorke

    dorke

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    Jun 20, 2015
  6. Minder

    Minder

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    General purpose diodes have been used successfully as steering diodes for many decades now.!
    Speed is not required in this application. I have personally used them this way for years.
    M.
     
    Last edited: May 15, 2016
    Bart Rydzynski likes this.
  7. Kiwi

    Kiwi

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    Jan 28, 2013
    Here is a nice video on diodes;


    I only keep two diodes for these sorts of simple jobs;
    1N4007 1A, 1000V
    1N5408 3A, 1000V
    I have never had an issue using either of these diodes.
    I also often solder them inline and put heatshrink over them.
     
    Michael-J and Minder like this.
  8. dorke

    dorke

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    Jun 20, 2015
    Well,
    Who said anything about speed?
    It's the Vf that makes all the difference!

    At about 2A and 25C
    The 1N5821 shottky diode will drop about 0.35V,
    while the 1N5408 silicon diode will drop about 0.85V.
    That is a significant difference in loss of voltage feed,
    and in a lesser way efficiency loss due to power dissipation.

    So,
    you have been doing something the wrong way for too many years,
    Maybe your application didn't "mind" the drawbacks.
    But,don't you think it is time to do it better?;)
     
    Michael-J likes this.
  9. dorke

    dorke

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    Jun 20, 2015
    Nice of you to put the video in.
    But,did you watch it and understand it ?
    The shottky diode is the way to go with such applications, not the silicon diode one.
     
    Bart Rydzynski likes this.
  10. Kiwi

    Kiwi

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    Jan 28, 2013
    Yes and Yes.

    Schottky diodes may be better for this application due to their slightly lower voltage drop, but are not an absolute requirement for simple circuits like this. General purpose silicon diodes may get slightly warmer, but will still work well in this application. There must be zillions of garden variety silicon diodes in use around the world in similar circuits.

    And yes, I have been doing lots of things wrong for many years. Probably too long in the tooth to change my error ridden ways.;)
     
    Minder likes this.
  11. Minder

    Minder

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    Apr 24, 2015
    +1 the 1N4007 is the first go to for me.
    Actually the one I linked to in Digikey covers all bases as a Fast switching diode plenty suitable for this purpose.
     

    Attached Files:

  12. Michael-J

    Michael-J

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    May 14, 2016
    Thanks for all the discussion. It seems like there are many diode options each with it's own pro's and cons. With a better understanding of what i should be looking for with regards to a diode, I found a pre-packaged diode that plugs into a standard automotive mini fuse holder (Cooper Bussmann 22903-6 6A mini Diode Fuse). The only issue now is that the only spec they give is that it is a 6 amp diode (they do have a 3A as well). I haven't been able to find any additional technical data on line so I e-mailed the manufacturer tech support and will hopeful see a response. This type of configuration will provide for the cleanest installation and allow for easy user service if ever needed. I also needed to install some relays and the fuse block holder allows for this as well. I'm hopeful the diode specs are similar to those recommended.
     
  13. Minder

    Minder

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    That product appears to be a diode only, no fuse Over rating on the current is no problem for the diode, do you have any other fuse in the circuit prior, looks like you would have to fuse separately?
    M.
     
    Last edited: May 15, 2016
  14. Michael-J

    Michael-J

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    May 14, 2016
    The overall circuit is fused at 15A and supplies multiple solenoids at the same time. They all have a common power source but I need one of the solenoids to have a secondary power source (thats what I am adding) that doesn't backfeed all the others if it is activated hence the need for the diodes in the existing feed and the one I am adding to that one solenoid. With the design of the fuse block, I could incorporate a separate 3A fuse upstream of the diode to protect the diode. As is designed, if the solenoid shorts out, existing wiring sizing and main fuse would prevent harness damage but diode would go first I would guess. It's only 2 jumpers and 2 ATM fuses to protect the diodes and there is space in the fuse block so it wouldn't hurt to add it in I guess.
     
  15. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Commercially available (Diode) battery isolators have been available from the marine electronics industry for decades. They're manufactured to live in extremely harsh environments.

    Chris
     
  16. elebish

    elebish

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    Aug 16, 2013
    I would use the schottky diode instead of the regular silicon but both will work fine. No rocket science here!
     
    Minder likes this.
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