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Need to draw 5 amps

Discussion in 'General Electronics Discussion' started by Anon_LG, Mar 2, 2016.

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  1. Anon_LG

    Anon_LG

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    Jun 24, 2014
    I require a 5 volt supply that is capable of providing 5 amps or more. I have found this, but it look as if I will have to wire the plug. If this is the case, is this safe?

    I feel it safer to go with a power supply that already has a plug pre-wired. I will be drawing five amps or more, with the RPI, the steppers, lights etc, and other than the one above, I can not find a supply that is able to supply enough current.

    I do not want an expensive benchtop supply, just a set 5 volt regulated (or higher) output. Budget on this one is dependant, I have to draw this off of an overall supply of £500 for the prototype.

    Thanks,
     
  2. Gryd3

    Gryd3

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    Jun 25, 2014
    LED Drivers are typically constant current, so you may find that one unsuitable.
    If you are looking for a budget 5V supply, take a look at old/new desktop PSU units...
    [​IMG]
    It's not uncommon for these to be able to pump out more than 10-20A . They have over-current protection and are fairly close to the regulated output.
    You also have a 12V and 3.3V output to play with.
    *Note that these sometimes require a load on the 5V line in order to properly regulate and output the 12V or 3.3V line.
     
  3. dorke

    dorke

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    And if needed a constant current circuit can be added to drive the part(s) that needs it.
     
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  4. BobK

    BobK

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    There are plenty of high amperage supplies for LED strips available on FleaBay.

    Bob
     
    hevans1944 likes this.
  5. davenn

    davenn Moderator

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    very, as long as you know how to connect a cabled plug properly ;)

    I have used dozens of these style of supplies for multiple commercial jobs.
    As long as the complete supply is housed in a box etc so that people cannot touch the screw terminals with their fingers, no problems

    @Gryd3 's alternative suggestion is also a good way to go :)

    Dave
     
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  6. hevans1944

    hevans1944 Hop - AC8NS

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    If you do go with the PSU you selected, you need to mount it in a box, wire a fuse and a power switch in series with the mains, perhaps add a neon power on indicator, and provide a strain-relief grommet where the power cord enters the box. You can purchase illuminated rocker switches with a neon lamp and ballast resistor built in. Another grommet should be used for where the DC wires exit the box. Use crimp-type spade terminals of the appropriate size to make connections to the power supply. Or do as @Gryd3 suggested and purchase an AT-type PSU which will have a power cord receptacle and a power switch already fitted.

    What is it you are trying to DO? Many LED strip lights are designed to work with constant-voltage DC, having the requisite current limiting circuitry built into the strip. Check your lighting strips to see what their voltage and current requirements are.

    Be safe, young man. Live long and prosper.
     
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  7. AnalogKid

    AnalogKid

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    Jun 10, 2015
    Note that while ATX power supplies do have overcurrent protection on the output, that protection does not kick in unto about 115% of the rated output current. So a 30 A output like the one in the photo will happily supply close to 35 A into whatever the load is if the load has a problem.

    ak
     
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  8. dorke

    dorke

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    Jun 20, 2015
    FleaBay ,spoken as a true Addams.
    Mui bien senior Gomez;)
     
  9. sureshot

    sureshot

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    The converted ATX is the favorite here, so long has you can convert one safley .I use the +5 and +12 volt rails output for many applications, and there a winner.
     
  10. Anon_LG

    Anon_LG

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    Jun 24, 2014
    I was dubious as to the desktop supply suggestion at first, expecting high prices. But I was wrong. This is, judging by the reviews and description, perfect.

    3.3, 5, 12 Volts
    High Wattage
    Low price

    This seems too good to be true. The bad reviews are only complaints on wire length, noise and build quality. None of which are a problem in my situation.

    This seems to be what I will be getting, it meets all requirements. This power lead to go with it.

    Due to multiple 5 volt outputs, I can power the Pi directly from this supply, can I not? As it is SATA standard, I assume that all outputs are properly regulated. This would be of great convenience as I would not require an additional Pi supply.

    Thanks,
     
  11. Gryd3

    Gryd3

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    Jun 25, 2014
    Ground is common of course, and the outputs are all regulated and pretty darn stable. They may not be exactly 5V ( 4.97V is close enough for most people )
    On 'some' supplies, they offer more than one 5V or 12V rail to pull from, but that's only the case with higher end PSUs.
    Once that arrives, there are three things you need to do to make it work:
    - Make an adaptor to plug into the PSU, or cut the plugs off and terminate the ends how you see fit.
    - Find the PS_ON wire on the large 20/24pin connector. This must be shorted to ground to turn on the power supply fully on. Consider this a 'soft power' switch, because there will be 'some' outputs in operation. Usually only on a couple wires as a 'standby voltage'. (This PS_ON wire is held to ground when the computer turns on... the standby power is provided for very low power items on the computer like BIOS, clock, and some basic logic)
    - If applicable, you may need to put a 1W or 3W resistor on the 5V output of the power supply to be able to use it to it's full potential. Some supplies will not properly regulate the 12V or 3.3V line unless there is draw on the 5V line... I have not actually found a supply that operates like this though... the 4 I have used have functioned great providing enough power for a Car Audio Amplifier and a small embedded PC for bench testing, as well as powering a 12V automotive 'emergency' air compressor :D
     
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  12. Anon_LG

    Anon_LG

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    Jun 24, 2014
    So this supply will only have one 5 volt pin to pull from? When I research SATA pinout, it shows several 5V pins. But there are several pin outs provided, is there a reliable source that states the pinout for the SATA connection present on this PSU?

    Thanks,
     
  13. Gryd3

    Gryd3

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    Jun 25, 2014
  14. Gryd3

    Gryd3

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    Jun 25, 2014
    Sorry! I may have worded that incorrectly. The ATX Power Supply will offer multiple voltages you can use at the same time.
    The power supply unit will typically only have 1 rail for each voltage, but multiple wires connected to that rail.

    So, there may be a 5V wire on 7 of the pigtails that come out of the PSU, but they are all the 'same' 5V supply.
     
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  15. Anon_LG

    Anon_LG

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    Jun 24, 2014
    OK, that explains it. So, for example, if I get a large transient on a 5 volt pin, and I have a Pi powered off of this, even on a other pin, the Pi could be destroyed?

    Your source for the pinout matches the one that I looked at previously, so I can be confident that the diagrams are correct.

    Thankyou,
     
  16. Gryd3

    Gryd3

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    Jun 25, 2014
    You are absolutely right with that assumption.
    You would need to wire your own form of protection on the Pi . If you accidentally shorted the 12V and 5V wires together for example, you would shoot 12V into the Pi.
     
    Anon_LG likes this.
  17. Anon_LG

    Anon_LG

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    Jun 24, 2014
    OK, in terms of protection I will not be able to use a simple blocking diode, a voltage drop will be present, making the output useless unless I boost it back up. But then comes the problem that these boost converters provide less than the 2 amps required by the Pi.

    So should I use a p channel FET with a schottky, according to the diagram.

    p-ch-fet-circuit.png
    This attached between the power supply and components likely to cause transients, such as voltage converters and motors, should prevent the large reverse voltages. I would change the value of the schottky though.

    Is this a good option or is there a preferable alternative?
     
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