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Adding a capacitor to a fuse for initial loading?

Discussion in 'Off-Topic Discussion' started by soggyBottom, May 19, 2023.

  1. May 19, 2023 at 5:49 AM
    #1
    soggyBottom

    soggyBottom [OP] Well-Known Member

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    I have a device that "can" run on 12v. When I plug it in to my cigarette lighter it blows 15A fuses. The device works fine on a big 40v power supply.

    The device is rated for 500w output, but I'm only ever really using about 100watts. it's just the initial moment when it's plugged in that the current draw is too high.

    I've seen electronics use a ceramic capacitors across a fuse and I'm wondering if I could do something like that here. Any ideas on where to start? I have a lot of electrolytic and ceramic caps.
     
    Last edited: May 19, 2023
  2. May 19, 2023 at 6:04 AM
    #2
    3JOH22A

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  3. May 19, 2023 at 6:12 AM
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    SR-71A

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    The point of fusing is to protect components of the system, ie the wiring, wire terminals, etc. If you are going to the length of modifying the factory system, Id just run a dedicated heavy gauge lead from the battery.

    Also I have the same question as above, what is this device? It operates at both 12v and 40v?
     
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  4. May 19, 2023 at 11:33 AM
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    soggyBottom

    soggyBottom [OP] Well-Known Member

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    This is it. It's actually a 500w LiPo charger. It has 2 inputs.

    1) 120vAC - 40vDC - charger

    2) DC input with barrel and xt60 in parallel

    Screenshot_20230519-122952.png
     
  5. May 19, 2023 at 11:36 AM
    #5
    soggyBottom

    soggyBottom [OP] Well-Known Member

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    I misspoke slightly. It accepts a DC input between 10v and 38v. I have my 40v DC power supply turned down to 38v.
     
  6. May 19, 2023 at 11:42 AM
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    Gutentight

    Gutentight Well-Known Member

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    I’m not an EE. Now that’s out of the way..

    I would think the capacitor would go in series just after the fuse to reduce the initial current surge through the fuse. Also consider it will still be live for a while after pulling the fuse (or blowing a fuse) unless you add some high resistance jumper.

    edit: Actually even if only using 100W it is a decent amount for the cigarette lighter. As suggested earlier you’re probably better off running a connection to the battery. 12ga wire should be good for a 25amp fuse and maybe then you can skip the capacitor. That would still be undersized if you used the full device capacity.
     
    Last edited: May 19, 2023
  7. May 19, 2023 at 11:47 AM
    #7
    0xDEADBEEF

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    How big of a current spike are we talking here? Is it just charging up some big capacitors?

    A thermistor or resistor would be a better choice to limit the inrush current.
     
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  8. May 19, 2023 at 12:36 PM
    #8
    Bivouac

    Bivouac Well-Known Member

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    Run a new circuit from the battery for the load you have and be done.

    Do you plan to add a timer to allow the cap to charge first before your device is energized .

    Your just adding even more of a demand on your circuit .

    It is your project do what you think best.
     
    SR-71A likes this.

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