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Which diodes I need?

  1. Aug 2, 2011 #1
    Hey, I have flasher module installed and I wanted to have flashing corner lights and turning lights from the same wire. Problem is when I would use corner lights, the turning lights will be on too and when I would use turning lights, corner lights will activate too.

    [PLAIN]http://bestpcreviews.com/uploads/thumbs/1312303226_photo.jpg [Broken]

    The problem is to have turning and corner lights flash, the lights must be connected, therefore when they do their original function, electricity connects to other light and they both work

    So solution is to use diodes, but I am not sure which numbers I need. Please help me because I don't know much about electrical engineering.

    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Aug 2, 2011 #2
    I didn't understand a bit of about what you are doing, except that you need a diode.
    You can try 1N4001
  4. Aug 2, 2011 #3
    lol, sorry about that.
    But bottom line is I need diode that will work with car power, which is 12v of course. Through the diode will go power to activate 35w foglights and turn signals.

    I looked at the number 1N4001 and it says

    * Forward Voltage: 1V

    * Forward Current: 1.1A

    * Repetitive Reverse Voltage (Max): 50V

    * Current rating: 1A

    * Package/Case type: DO-41

    So I am confused, if car runs on 12v, how come the 1N4001 says 1v, will it work or I need another diodes?
  5. Aug 3, 2011 #4
    The 1V is forward Voltage Drop. You should look for reverse voltage(50V), which is way more than 12V.
    So, voltage wise, its fine.

    But, since you need 2.92A (35W / 12V ), its 1A rating isn't sufficient. You need to use 3 in parallel or use 3A diode, 1N5401
  6. Aug 3, 2011 #5
    Thanks a lot for your help!
    One more question, as I understand, even though its one flow diodes, low voltage still goes opposite way, so I was wondering, will I have problems with that? or the opposite voltage would be too low to even light up LED light?
  7. Aug 3, 2011 #6
    Diodes in parallel is generally a 'no-no'.
    If the forward voltage drops are not IDENTICAL, one of the diodes will carry the brunt of the current and will be subjected to thermal runaway.

    This author did a nicer job of explaining it than I can...

    You could add resistors in series with each of the diodes to help balance the load (the resistors would handle the imbalance), but you're better off just using one diode IMO.
  8. Aug 3, 2011 #7


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    It may be worth pointing out that you would never connect a diode across 12V in the forward direction - there would always be a resistance (bulb or whatever) in series. Under that condition, there would be a bit under 1V drop across the diode and 11V across the device. Direct connection would just fry that (or any other, beefier) diode because a massive current could flow.

    For a 3.5A foglamp, the diode should be one that is specified for up to, say, 5A forward current. The 1N4001 would cook. There are plenty around to choose from, though. Get a cheap, automotive type.
  9. Aug 3, 2011 #8
    Thanks a lot. So 5a should work for all car lighting applications? What do you mean by automotive diodes? They are designed specifically for auto? How can I find those on ebay? What I need to type in search to find those?
  10. Aug 3, 2011 #9
    Thanks for that.
    I_am_learning. :)
  11. Aug 4, 2011 #10


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    Look in a catalogue of semiconductors and find one with suitable parameters. It's really not critical in this case - just make sure the current is high enough. In some lists they describe the application - because they are often presented in number order. You shouldn't't need to spend too much on a 'high performance device'.
  12. Aug 4, 2011 #11
    Sorry, I don't understand what you mean by diode across 12V in the forward direction

    I wanted to connect wire with diode to positive wire for turning signal and I don't want the turning signal power up the wire with diode.

    Also, would this one work for me?

    SR540 5A 40V

    DO-201AD package

    Max, recurrent peak reverse voltage : 40V

    Max. RMS voltage : 28V

    Max, DC blocking voltage : 40V

    Forward voltage : 0.60V at 5A

    Operating temperature range : -65℃ ~ +150℃

    Storage temperature range : -65℃ ~ +150℃

    Typical junction capacitance : 200pF

    Body dimension : 5.5x9.5mm Dia x L

    Lead length : 25.4mm, min
  13. Aug 5, 2011 #12


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    That diode would be fine for supplying enough ( 5A) to any lamp but a headlamp, i should imagine.
    It would help me (and you probably) if you drew out a proper schematic diagram of what you want to do. It is just not at all clear to me why you should need a diode at the moment.

    You know the sort of thing. A line across the top with 12V on it and a line along the bottom for Ground. The various bits of circuit will take current from top to bottom via lamps, switches and your diode. Believe me, they are a terrific way of understand what will actually happen when connected up. A bit of 'discipline' at the start will do the business for you.
    Remember, the actual routing of the wires is irrelevant; it's what they connect to what that counts. That's what annoys me about so many automotive circuits - they are obsessed with keeping the wire in the looms which is great for tracing, blindly, but makes understanding the actual function very hard. You can bet that the designer didn't use what you find in the workshop manual.
  14. Aug 6, 2011 #13
    Thanks, well, let me try to expalin and if that won't help, I'll try to draw again.

    I have flasher device and want to use the device on my corner lights and my turning lights at the same time.

    To do that, I need to connect positive wire to corner light and to turning light. (same wire/connection)

    If I do that, corner and turning lights will flash through the flasher device, but if I just want to turn on corner lights, it will also turn on turning lights because of the positive wire that is connected to both of these lights (wire coming from flasher device)

    That's why I want diodes so that when corner lights are on, power will not go back to flasher device or to turning light and when I use turn signal, power from it not going to go back to flasher device or to corner lights.

    Hopefully that explains it :)
  15. Aug 7, 2011 #14


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    I see. 12v from one wire turns on one light. 12v from the other wire turns on both. Diode between live end of both bulbs will do it. All that's needed is a needy enough diode.
  16. Aug 7, 2011 #15
    Thanks. 5A diode? Can you tell me which specific diode model I need?
  17. Aug 7, 2011 #16


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    I suggest the cheapest 5A diode you can get. There's no point in my giving you a type number. Use your local electronics store or an internet supplier. It is non-critical - just go for 5A max forward current rating or above.
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