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Trying to determine the size of Diodes required

  1. Mar 14, 2017 #1
    Hey All, i just joined today to try and figure out what size of diodes i need for the project im working on.

    I am working on installing a new Light Bar and Flood Lamps to my Jeep to get better light at night.

    This is my hope to accomplish:

    Relay 1 will be used to turn the LED Light Bar and Both Side Floods on when i activate the BRIGHTS in my headlights. The power for this relay will be controlled by RELAY 2, which will allow me to control whether or not the LEDS come on when the Brights are activated (I dont want LED's on when im driving on Freeways in cities). Relay 2 will be controlled by a switch in the cab of my vehicle.

    This is where it gets tricky...

    I want to have functionality to be able to turn JUST the Right Flood ON or JUST the Left Flood ON when im doing my security checks at night, without the LED Light Bar on at the same time. Relay 2 Controls just the Left Flood, Relay 2 Controls just t he Right Flood. Those will both also have swiches in the cab to control the on/off feature. Ive circled where im sure i need the Diodes to go, just unsure what direction to install them and what size i need to install.

    Attached Files:

  2. jcsd
  3. Mar 14, 2017 #2
    Welcome @DakotaE to Physics Forums!

    I would help you to choose such a diode which will work perfectly in those circled regions.

    For High Current like a 6Amp supply of 12 Volt. You need to consider such a diode whose Reverse current is minimum and high operating temperature handling capabilities (Because at 6A, things would get hot enough). So Its better to choose such a diode which would work in all the conditions (specifically for your application).

    I would suggest one of the following diodes to be connected:-
    1) 6A10 (MIC)
    Mounting Style: Through Hole
    Package / Case: R-6
    Vr - Reverse Voltage: 1 kV
    If - Forward Current: 6 A
    Type: Standard Recovery Rectifiers
    Configuration: Single
    Vf - Forward Voltage: 900 mV
    Max Surge Current: 400 A
    Ir - Reverse Current: 10 uA
    Series: 6A10
    Packaging: Reel
    Height: 9.1 mm
    Length: 9.1 mm
    Maximum Operating Temperature: + 175 C
    Minimum Operating Temperature: - 65 C
    Operating Temperature Range: - 65 C to + 175 C
    Termination Style: Through Hole
    Width: 9.1 mm
    Unit Weight: 0.074075 oz

    2) 10A10 (MIC)
    Part No: 10A10
    Repetitive Peak Reverse Voltage(VRRM): 1000V
    RMS Reverese Voltage: 700V
    FWD Voltage(VF): 1V@10A
    AVG Rectified Output Current: 10A @ 50C
    Peak Reverse Current(IRM): 10uA @25C and 100uA @ 100C
    Typical Junction Capacitance: 80pF
    Typical Thermal Resistance Junction To Ambient: 10C/W

    The above two listed diodes are best suited for your application.

    Choose any one of them, buy them at



    Connect them in a Positive biased configuration, this would make it possible to switch the lights at any desired time.
  4. Mar 14, 2017 #3
    I just looked at my notes, and the lightbar is actually 10 amps (24 x 5 watt diodes) Is the 10A10 higher capacity then the 6A10? i dont know anything about Diodes. Im assuming the side with the little mark on it goes the battery side? what side of the diode would i hook to the LED Flood Lamp To?
  5. Mar 14, 2017 #4


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    Having a little trouble understanding what you want. A truth table would be nice. Chances are if you do your relays right all you need is a couple of small signal diodes that are able to handle relay coil current. Not full load current.
  6. Mar 14, 2017 #5
    Averagesupernova, what im trying to accomplish is isolating the flood lamps from backwards voltage so i can either run both floods and the lightbar at the same time using one switch, or i could use one of the floods without the other flood and the lightbar from illuminating using a separate switch. I need to install diodes where i have circles on the diagram. I need to know how big of a diode to install to keep the voltage going only one way from the Lightbar feed. I hope that clarifies what im wanting to do.
  7. Mar 14, 2017 #6
    The lightbar is 10 amps and each flood lamp is 1.5 amp
  8. Mar 14, 2017 #7


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    Science Advisor
    Gold Member

    I wouldn't wire it that way. One relay per light or set of lights. Why be tying them together after the relay where you have to deal with full load current? Do the diode work on the wires that feed individual relay coils and deal with much lower currents.
  9. Mar 15, 2017 #8
    OK - in your desired scheme: R1 + R2 = All lights on, R3 = Just the Left, and R4 = Just the right.

    In the way you have it The Blocking diodes ONLY need to carry the current of the side lights when R1+R2 are on. ( individually 1.5 A)

    Connect them like THIS - the banded end of the physical diode, is the "bar" end in the symbol. (The diode will NOT carry any current needed by the main light bar , so they do not need a > 10A rating)

    So you want 2 diodes, rated > 1.5 A and > ~20 V.. THESE 100V. 6A diodes will work. Radio Shack does not have them on line, but I'll bet a few calls to the local stores you can fins one package.

    As Averagesupernova pointed out you can you can also do this with the relays, and use a smaller diode, I probably still would not go below 1 A - Example - Clearly RadioShack can not count,,,,I will miss having SOME source of components immediately available.
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