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Adding accessory power to a DC power input?

Discussion in 'Power Electronics' started by jsovey, Oct 23, 2020.

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  1. jsovey

    jsovey

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    Oct 23, 2020
    I'm looking to add accessory power to field monitor that runs on 15v DC ( via ac/dc wall adapter) or a large battery (also 15v DC) I would like to run wires from the two 4pin-XLR power inputs to an accessory power tap but work whether it's plugged into either or both power sources. I'm pretty new to electronics so need help. I made up a schematic in EveryCircuit to test. The power inputs are two 4pin XLR and are represented in the schematic as "voltage sources". ( Schematics show power from either and both power sources) The accessories are represented by an LED (but would be a power tap to plug in the accessories) it looks like a diode coming out of either positive would protect the battery. I was afraid if I plugged into the wall adapter and a battery the accessories would get double the Voltage or current but EveryCircuit says its looking safe. Much appreciated! Back.jpg Both.jpg Wallpower.jpg Battery.jpg
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    Your schematic looks good.
    No way. The power source with the (slightly) higher voltage will power the device. Voltage sources in parallel do not add up. Current draw is determined by the load, not the voltage source.

    Note that the output of the circuit after the diodes will be slightly less than the input voltage from the battery or Dc power supply. Each diode results in a loss of about 0.6 V to 0.7 V. That should be no problem as there has to be an internal voltage regulator within the device to account for varying battery voltage.
     
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  3. jsovey

    jsovey

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    Oct 23, 2020
    Thanks, appreciate it!
     
  4. Alec_t

    Alec_t

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    Jul 7, 2015
    Just make sure that the added power consumption of the accessory doesn't overload the supply.
     
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  5. jsovey

    jsovey

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    Oct 23, 2020
    Any advice on what diode would be safe to use?
     
  6. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    That depends on the current drawn. The labels next to the XLR inputs show 6 A and 7 A respectively.
    Add the additional current for the accessory. Example: accessory requires 1 A, therefore max. current is 7 A + 1 A = 8 A. A 10 A diode has enough headroom to be on the safe side. Here's an example list of suitable Schottky diodes (I selected Schottky diodes for their lower pass voltage over Silicon diodes). Note that an additional heatsink may be required.
     
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  7. jsovey

    jsovey

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    Oct 23, 2020
    Great info, Thank you all so much! Excited to solder it up.
     
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