1N4148 Logic Diode to Relay

Discussion in 'General Electronics Chat' started by Mastermind, Dec 27, 2011.

  1. Mastermind

    Mastermind

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    Hey guys,

    I am soldering a 1N4148 Logic Diode to this relay
    http://www.amazon.com/Parts-Express-1N4148-Logic-Diode/dp/B0002KRC7C

    I am using this diode to dampen the reversed polarity high voltage pulse when removing the voltage from the relay.

    I am basically just using the relay and this rocker switch as a high current allowing on/off switch.
    http://www.amazon.com/gp/product/B001TQKKMC/ref=oh_o03_s00_i00_details

    I am having trouble figuring out where to connect everything. Heres what I have so far.

    Diode soldered onto terminals 85 and 86 (Which way do I solder the diode on? Also which side of the diode is anode and which side is cathode?)

    Input: terminal 87
    Output:terminal 30

    Where do I put the rocker switch? On the input?

    Thanks
    Mastermind, Dec 27, 2011
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  2. Mastermind

    GonzoEngineer VIP Member

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    Got any information on the relay?..that might help us to help you.

    How about a wiring diagram? so we know more of what you are trying to do.
    GonzoEngineer, Dec 27, 2011
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  3. Mastermind

    Resqueline Moderator

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    The "bar" on the diode goes on the positive terminal of the relay.
    You can have the switch (& also the load) on the negative or the positive side according to what is most suitable (beneficial) for the wiring.
    85 & 86 are strictly speaking interchangeable, as are 87 & 30.

    Attached Files:

    Resqueline, Dec 28, 2011
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  4. Mastermind

    Mastermind

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    Sorry I intended to post the information http://www.amazon.com/gp/product/B001PNMBE4/ref=oh_o02_s00_i00_details

    Here's a little schematic I made on my whiteboard
    http://www.electronicspoint.com/attachment.php?attachmentid=3252&stc=1&d=1325039215

    Ok heres what I understand.
    Picture in next post because it wouldn't allow me when editing

    The diode would look like this then - ---------------------[ |]------------------------- +

    Attached Files:

    Last edited: Dec 28, 2011
    Mastermind, Dec 28, 2011
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  5. Mastermind

    Mastermind

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    Attached Files:

    Mastermind, Dec 28, 2011
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  6. Mastermind

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    I don't understand your diagram.

    What are you trying to do?

    Are you charging two 12 volt batteries in series?
    (*steve*), Dec 28, 2011
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  7. Mastermind

    Mastermind

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    That's what I am trying to do. I could not find a high current allowing switch so I have to use a relay instead
    Mastermind, Dec 28, 2011
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  8. Mastermind

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    You don't need a diode if you're using a switch. It's really only needed if you're switching the relay using a semiconductor device. (in any case, you'd need to use a higher powered diode)

    Look at Resquline's answer above (just remove the diode).

    BTW, you still haven't said what you're trying to do. I see two 12 volt batteries in series in your diagram. I hope you're using a 24V relay (or is there only one battery?)
    (*steve*), Dec 28, 2011
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  9. Mastermind

    arg733

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    Hi

    the black line indicates the cathode and the other side of the diode is the anode
    you need a flyback diode connected parallel to the relay with the cathode pointing to the + and anode from - (anti parallel) otherwise you may see sparks when closing the switch because of the hv pulse generated when you cut power to a coil. The same is with semiconductors. MOSFET should be ok as they have a small leakage but if you use IGBT the pulse will destroy them.
    you can also use an array of 5 or 10 IGBTs instead of the relay (the relay has a limited number of switching times whereas the IGBT or MOSFET can be switched on and off indefinitely.

    hey that is a very low voltage diode why dont you use a 500v or 1000v ? the pulse of the relay could be more than 200v. I dont understand your circuit but i think you are using the diode the wrong way. You should use it as a flyback diode.
    arg
    Last edited: Dec 28, 2011
    arg733, Dec 28, 2011
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  10. Mastermind

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    The voltage rating of the diode would only ned to be sufficient to withstand the operating voltage of the relay (e.g. 12V?)

    The current through the diode will be aproximately the same as the operating current of the relay.

    You only get a high voltage if the diode is absent.
    (*steve*), Dec 28, 2011
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  11. Mastermind

    Mastermind

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    That's where the 1N4148 diode comes in. The point of the diode to suppress the high voltage rebound pulse and keep the current flowing in one direction. I am using a diode to increase the life of my relay.


    Steve:

    There are two 12 volt batteries in series. I am using a 12 volt 80 amp relay.
    Mastermind, Dec 28, 2011
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  12. Mastermind

    jackorocko VIP Member

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    No actually the freewheeling diode directs the current flow back into the inductor. This cycle repeats till the diode has used up all the stored energy. This will not increase the life of your relay, but it will protect other sensitive parts in the circuit against high voltage spikes. The coil in the relay is nothing more then an inductor and it needs to release it's stored energy somehow.
    Last edited: Dec 28, 2011
    jackorocko, Dec 28, 2011
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  13. Mastermind

    Mastermind

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    Oh ok I understand. I'm going to use the diode even though it may not be necessary.

    Requeseline:

    Thanks for the diagram. What does the 12 volts mean on your diagram?

    I also found this diagram which is pretty much the same as yours. The dotted line should be disregarded.

    Attached Files:

    Last edited: Dec 29, 2011
    Mastermind, Dec 29, 2011
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  14. Mastermind

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    You can't use a 12V relay from a 24V supply (well you can. but it won't last very long). You need a 24V relay.

    If you're switchng 24V than youalso need a relay with contacts rated for 24V.

    The easiest way of doing this is to get a relay designed for use on a truck since they often have 24V electrical systems.

    The 1N4148 is the wrong sort of diode to use in this application. You really should use a rectifier diode rather than a small signal diode. A 1N4001 or 1N4002 would be more appropriate.

    Or are you using 12V to switch 24V as per your last diagram?

    We're still guessing because you haven't told us what you want to do. But hey, if you just want answers (and not good answers) then who am I to argue.

    The diode across the relay is needed in your circuit above because you have a LED which would be subject to large reverse voltages if you didn't (and all the better reason to use the correct diode).
    (*steve*), Dec 29, 2011
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  15. Mastermind

    Mastermind

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    ok here is my scenario. I could not find a switch that could pass 48 amps so I am using a relay that is energized when a mechanical switch is turned on. Only my motors operate at 24 volts. All the other electronics runn at 12v or lower. Will my 12v 80 amp relay still work? As I understood it, this relay needs a minimum of 12v to run properly, but it will be able to run at 12v. Maybe I was taught incorrectly.
    Mastermind, Dec 30, 2011
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  16. Mastermind

    GonzoEngineer VIP Member

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    Just build it....and tell us how it went!:D
    GonzoEngineer, Dec 30, 2011
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  17. Mastermind

    Mastermind

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    I would, but I'm on a low budget because I'm 14 (also explains my newbieness and inexperience).
    Mastermind, Dec 30, 2011
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  18. Mastermind

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    OK, not too hard to find a switch rated at 48A, but probably not cheap eaither. Look at battery isolation switches for example.

    You need to make sure the relay is rated for a continuous 48A load -- or at least rated for the duration you wil leage the load powered.

    A 12V relay will operate from a range of voltages, perhaps 10 to 16 volts, but outside of that you will have problems. Again, reading the specs of the device will be the sure way to tell. Operating it from 24V is almost certainly going to be very bad.

    If you're using 2 batteries for the 24V, then jut use one of them to power the relay.

    Be a little careful because this will cause one battery to drain slightly more than the other which is a consideration whilst recharging them (how do you intend to do that?)
    (*steve*), Dec 30, 2011
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