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Voltage Regulation

Discussion in 'Power Electronics' started by PowerSet, Jun 27, 2020.

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  1. PowerSet

    PowerSet

    6
    0
    Jun 13, 2015
    Hello all, I am most of the way through a project and was looking for a little help, since I am not well versed in electrical components.

    My concern is with a high current power supply and low current devices. In the past I thought that most devices typically only accepted the amperage they could handle, and I’ve never had a problem using high amp power supplies for anything before, but today I tried powering two old 12v powered usb hubs, and they did not like the power at all and blew a capacitor right next to the power input.

    I am guessing this happened because they were extremely cheap Chinese junk from a few years ago, but I would like to try to regulate the output regardless to be safe.

    Basically I have 12v capable of 40+amps, going to multiple outputs for various projects, and I would like to limit the maximum available current.

    I would like this to be able to power various 12v devices, so I don’t want to use resistors calculates for a specific load, and although not extreme priorities, budget and efficiency would be nice to keep in mind.

    It seems like there are a few options, and with my limited knowledge I am not sure what would be best, and there are a few things I’m completely unsure of.

    I would also like to include a fuse for each output, and some of my research makes it sound like a fuse would limit my current, but I believe there is more to it than that.


    So to limit the maximum available current from a 12v 40a source, would a 5a fuse be suitable to limit 5a output, or will the fuse just blow because more than 5a is attempting to be drawn?

    Would an in line voltage regulator be an option? Most that I see are step down converters, and I don’t think they can go from 12v to 12v, but I am guessing there are regulators or something similar that aren’t step down modules.


    Any advice would be appreciated, I just want to have some protection for any devices I power with this!
     
  2. duke37

    duke37

    5,364
    769
    Jan 9, 2011
    A 40A fuse should protect the 40A power supply. No fuse will protect the drven devices, they will take what current they like. A fuse in each supply will help if the device is faulty. 12V at 40A is plenty to start a fire.
    Fuses do not limit current unless they blow. A 12V bulb can be used as a current limiter.
    There are convertors which can raise the voltage and others which can decrease the voltage. It is possible to get convertors which can do both but these are more complcated and expensive. The convertors can have current limiting built in. You could boost to 15V, then buck to 12V.

    If a 12V device fails with supplied 12V of the correct polarity, it may be that it has been sitting doing nothing for too long and the electrolytic capacitors need reforming.
     
  3. PowerSet

    PowerSet

    6
    0
    Jun 13, 2015
    I am definitely aware of the potential hazards of high amperage, which is why I’m here, and that’s what I thought as far as fuses, it sounded very odd to me to limit the output current with a fuse, since I’m pretty sure it would just cut the connection when too much current passes through.

    I have never experienced an issue like that before, and assume it was due to the old cheap devices I was using, so I definitely want to be safe with this and figure out what the issue was, which still seems to be a high likelihood of the hub itself being cheap and old.

    So in theory, if I have a 12v 40a supply, going to 4 devices, that will draw 12v at between .2 and 3.5 amps, there should be need for anything else to make the attached devices work correct?

    I only planned on having 4 outputs, for a few different 12v items normally run by 12v 2.5a wallwarts, with a 5A fuse before each connection.
    I don’t think the fuses are necessary, but anything I do adding auto electronics I always fuse, and I can’t see a downside to it.

    I did not think about using a boost converter to bring the voltage up, and a buck converter to bring it back down to a regulated 12v at a limited amperage, but it seems like it would be an inefficient way to do it, and hopefully something that is not necessary.
     
  4. duke37

    duke37

    5,364
    769
    Jan 9, 2011
    It is often said that a fuse only protects the cable, not the device. You do not want 40A to be fed through a thin cable. Look at each device and fuse to somewhat larger then the demand. I would venture to suggest that 1A would be enough for most pieces of equipment.
    A scrap fuse array out of a car would make a safe distributor.

    Boosting and bucking is messy but not too ineffivient with switch mode supplies. Why do you want to generate 12V when you have it at the start?
     
  5. PowerSet

    PowerSet

    6
    0
    Jun 13, 2015
    I didn’t want to generate 12v, but limit the maximum current. But it’s only because I’m a COMPLETE idiot and was completely wrong about how wires are labeled. I repurposed some old connectors from dead wall warts, and I could have sworn the wire with dashed marking was the negative, and it didn’t help that I was initially testing it with an old linksys router that apparently works whether the center pin is negative or positive.


    Boy do I look dumb.
     
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