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diode for collapsing magnetic field

Discussion in 'General Electronics Discussion' started by Blank Stare, Oct 10, 2012.

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  1. screwball

    screwball

    89
    1
    Jan 9, 2012
    Like so ;)

    EDIT just only seen there was more than page 1 lol
     

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  2. Blank Stare

    Blank Stare

    48
    0
    Oct 10, 2012
    OK, hope I didn't make a complete fool of myself here. I'm still getting over being sick, but I am going "stir crazy", stuck in the house.

    Let me see if I can address each paragraph, so that I am certain that I am following...

    It is manufactured by a company called "Viaire". I do not know the model number, off-hand, but if the label is still on the pump, under the hood of the truck, I will get it, and let you know.

    It has a 100% duty rating, which is to say that it's designed to run continuously, without overheating.

    Actually, believe it or not, I did.
    I started with a flow chart, and visited another forum, (which I can no longer find the URL for,) and they took my cocktail napkin, and started offering me suggestions. Over the course of several weeks, I had managed to draw what I had designed, with the help of knowledgable people like yourself. Like you, they were very patient with me, as I stumbled through the steep learning curve.

    What you see is the compact, final drawing, which I created in paint shop, and used to build/install the system into my truck.

    KrisBlueNZ...

    OK, the power relay is fed by either the the diode coming off of the SPDT, or the one coming off the Automatic Pressure Switch, depending on whether the system is on automatic, or over-ridden by the momentary manual switch.
    CHECK

    The relay coil is inside of the 1-1/4" black relay cube. I have used them rated 30 amp and 40 amp. I have use one rated 50 amps - they all failed, eventually - some faster than others. I understand that this is from "back EMF", that occurs when the relay's EMF collapses.
    CHECK

    The automatic pressure switch is all hardware, no electronics. It works strictly on the physical pressure in the tank of air. It has no coil - I think we can discount that possibility.
    CHECK

    That is NOT to say that breaking the auto press switch connection doesn't cause or contribute to the "back EMF", only that it does not appear to have any contact damage. - I am able to visually inspect this component.
    CHECK

    I'll take your word about watching an LED to verify "back EMF", I have no doubt whatsoever that this happens.
    CHECK

    To date, I have not had any switches or LEDs go bad - just the relays themselves.
    CHECK

    The traditional way is clear, and you are correct - that is exactly what my friends were talking about.
    CHECK

    QUESTION
    I believe this is exactly the problem we are discussing. Assuming an amp reading of 30, and a 12 volt DC system, would you recommend the same 1n4001 diode?

    QUESTION
    The pump is shut off by pressure sensitivity. I believe it is always the first switch to open it's contacts, but last to close them. Again, completely mechanical. If I understand you correctly, you are telling me that an arc across the auto press switch makes it back to the relay, also causing arcing?

    QUESTION
    Since it couldn't hurt to add a diode at the pump, I'm happy to do so. Which would you recommend?

    QUESTION
    There is never a time when the relay, or any switch, for that matter needs to open or close fast, to satisfy the system's purpose. It is usually no less than several minutes, before the pressure switch calls for power again. - Does that change the need for the zener diode?


    Thanks, screwball, I believe that is exactly where this discussion is heading.

    Based on our discussions so far, here is an updated drawing of what I THINK we have come up with so far. the two proposed diodes are in the green circles. I am not sure about the diode at the pump - I think we talked about a different spec there, but I must have missed it, somehow.

    I have spread the components out, so as to make the drawing easier to read.

    Am I getting any closer to seeing the light? :D
     

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  3. screwball

    screwball

    89
    1
    Jan 9, 2012
    Looks like its getting there :p
    Do you understand the purpose of the diodes across the motor and relay?

    After re looking over it, i noticed the diode over the relay would keep the relay magnetized after pressure switch being pressed and released, id imagine you dont want that to happen?

    If not then the diode that is across the relay, disconnect the cathode from the coil and connect it to the relay switch common pin (or between that and after the 30amp fuse)

    Also i dont the ratings of the 1N4001 diode but it wants to be enough to take the current that the motor takes otherwise it may blow when pressure switch is released
     
    Last edited: Oct 17, 2012
  4. BobK

    BobK

    7,682
    1,688
    Jan 5, 2010
    The diode across the pump needs a 30A rating at least (same as the pump)

    Bob
     
  5. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

    4,960
    651
    May 8, 2012
    Yes, you have to flyback diodes oriented correctly.

    FYI, you're not a complete novice. They don't draw schematics like that. Theirs are more akin to a very confusing puzzle. :D

    Chris
     
  6. Blank Stare

    Blank Stare

    48
    0
    Oct 10, 2012
    Thanks

    I actually understated my professional experience.

    I did start out as a Painter, and I still do some, in my semi-retirement.

    However, I was also a building / remodeling contractor at one time.

    Drawing circuits isn't all that different from drawing structural blueprints, once you know what the pieces look like, and where to put them.

    I will admit, however, that I have dozens of hours in previous drawings, before I managed to draw this "clean" one.
     
  7. Blank Stare

    Blank Stare

    48
    0
    Oct 10, 2012
    But, but, I am as dumb as a paper bag full of hammers...

    OK, I'll ask the obvious dumb question;"What number would that be?" I have no idea how to select a diode, unless someone advises me.

    Thanks,

    ~ Blank Stare
     
  8. CocaCola

    CocaCola

    3,635
    5
    Apr 7, 2012
    This thread is coming around full circle, Steve advised you how to search for such a diode way back on Page 2 I believe... Digikey as well as Mouser have searches that allow you to easily narrow parts do based on perimeters you choose... Choose diodes greater than or equal to 30 Amps if that is the motor rating, preferably a little higher just to give some head room...
     
  9. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

    4,960
    651
    May 8, 2012
  10. screwball

    screwball

    89
    1
    Jan 9, 2012
    Thats a hardcore diode haha not seen one like it

    Anyhow, just to repeat my previous statement incase it was missed, the diode across the relay coil would keep the relay closed even when the pressure switch is released right?

    The path through the diode and through the coil to ground is easier than the path through the motor then to ground so it would almost definitely keep the relay closed when the pressure switch is released?

    The cathode of that diode would go to the 30Amp fuse potential or stay where it is but a PTBS or something to break the flow to allow the relay to reopen and stay open until pressure switch is pressed again
     
  11. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

    4,960
    651
    May 8, 2012
    You lost me. The coil diode may delay the opening of the contacts a tad but we're taking milliseconds here.

    Chris
     
  12. CocaCola

    CocaCola

    3,635
    5
    Apr 7, 2012
    On this subject I was just sourcing some small reed relays for a project and much to my surprise the one I selected has the option of a built in coil diode for no additional cost... A nice little perk that saves one component...

    Resume normal thread...
     
  13. screwball

    screwball

    89
    1
    Jan 9, 2012
    I am thinking that when the pressure switch is pressed, current flows through the relay coil to close the relay, now the relay is closed, current is able to flow through the relay diode all the time therefore keeping the relay coil energized, therefore keeping the relay closed always

    Do you kind of get what im trying to say?
     
  14. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

    4,960
    651
    May 8, 2012
    Unfortunately, not even kinda!

    Chris
     
  15. screwball

    screwball

    89
    1
    Jan 9, 2012
    Just quickly drew up practically part of the circuit that was last attached in this thread i think
    SW1 is the pressure switch
    I simulated with bounce, faults etc and it still does what i am saying (keeps the coil energised)

    Do you see what im saying any better now? I most probably have misinterpreted something or have lack of knowledge somewhere along the line, if someone could clear it up for me then that would be great :)
     

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  16. BobK

    BobK

    7,682
    1,688
    Jan 5, 2010
    I get what you are trying to say, but it is not correct. The current decreases due to losses in the coil resisntace and the diode until it is zero.

    Bob
     
  17. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

    4,960
    651
    May 8, 2012
  18. screwball

    screwball

    89
    1
    Jan 9, 2012
    I see, so the slowly decreasing current is what would physically keep the relay closed until theres not enough current then the relay opens?

    is there any online examples that could teach it well exactly how and what happens? or what I need to read up on to learn it well? thanks
     
  19. screwball

    screwball

    89
    1
    Jan 9, 2012
  20. CocaCola

    CocaCola

    3,635
    5
    Apr 7, 2012
    That's my response as well...

    That's actually wrong as well, it should be grounded on the lower side (as pictured) not the positive switch leg... Diode should be tied parallel to the coil...
     
    Last edited: Oct 18, 2012
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