PSU -- Wiring type -- Fuse -- DMM

Discussion in 'Power Electronics' started by Tech_Elect, Feb 13, 2019.

  1. Tech_Elect

    Thread Starter New Member

    Feb 13, 2019
    8
    0
    Hi,
    I have a PSU 250W fsp that I connected to a car radio, I have advised to connect together the yellow and yellow/black cables that are at
    +12V and at different amperage 8A (yellow) and 14A (yellow / black)
    using an AWG 8 cable and a 25A fuse.

    -Is this cable suitable or should I use another cable of a different type?

    - It is necessary to do this or it is sufficient the supplying cable
    +12V - 8A (yellow) already with the 15A radio fuse (blue)?

    I'm not sure of the amperages of the various cables
    (data plate psu apart)
    I would like to use a DMM to read the amperes on each cable.
    I've never used it on a PSU for pc.

    -Can it be done or is it inadvisable to do it?

    Thanks
    Regards
    [​IMG]
    [​IMG]
    [​IMG]
     
  2. dl324

    AAC Fanatic!

    Mar 30, 2015
    8,754
    2,118
    Can't tell what the wire gauges are from the photo, but none look to be #8.
    Can't say without knowing the currents in question. Where is the yellow/black wire being fused?
    It'll be more convenient to use a DMM with a clamp on current "probe".
    What do you mean by "it"? Measure current, assume a 15A fuse is appropriate, ...?
     
  3. AlbertHall

    AAC Fanatic!

    Jun 4, 2014
    8,171
    2,027
    Connecting the two +12V supplies together may be problematic unless they come from the same regulator inside the supply.
    If they have separate regulators then the one with the higher voltage (however slight) will supply all the current until it hits its current limit and that might shut down the whole supply.
     
  4. Tech_Elect

    Thread Starter New Member

    Feb 13, 2019
    8
    0

    Hi,
    yes, the wires in the picture are smaller than awg8
    (both those of the radio and those of the PSU)

    awg8 is what they advised me to use if I connect the + 12V cables of different amperage (as written on the plaque of the psu)
    example connect an 8A + 14A cable (always at + 12V) and get
    22A (which is why you have to use a larger section cable)

    the 15A blue fuse is on the yellow + 12V wire of the radio
    the yellow cable of the + 12V radio is connected to one of the + 12V 8A (yellow) cables of the PSU
    the black (ground) of the radio is connected to a black (ground) of the psu
    (as you can see from the picture)

    the yellow / black wire of the psu (+ 12V 14A) has no fuse at the moment and is not used (it is isolated)
     
  5. Tech_Elect

    Thread Starter New Member

    Feb 13, 2019
    8
    0
    Hi,
    it seems to me that for this model of psu the 12V voltage regulators are separate but I'm not sure even if on the data plate of the psu is written that both are at + 12V

    so I imagine that connecting them together would not be 22A that is the sum of the currents 8A + 22A but if the one with the highest voltage suppose is that to + 12V 14A then perhaps the current would be not higher than the max that is 14A
    is this what you mean?
     
  6. AlbertHall

    AAC Fanatic!

    Jun 4, 2014
    8,171
    2,027
    This isn't the certain result, but it is a possible result depending on design of the particular power supply.
     
  7. Tech_Elect

    Thread Starter New Member

    Feb 13, 2019
    8
    0
    of course
    we can only make assumptions since we do not have
    the scheme of the specific psu

    in conclusion it would be better not to connect the two + 12V cables together with different amperage

    I do not understand why they have advised me, perhaps mistakenly, to connect the cables together

    this is what they was told me:
    "summing them just means to put them together, you theoretically should get 22 amperes from doing this. Youre going to want to have a pretty short lead from the PSU and get a thicker wire from there to avoid the wire heating up.

    sum them as close as you can you the PSU, and use a bigger cable from there to connect your stuff

    he 12 volt wires are usually coming from a singular transformer, just split into multiple wires so that the molex plugs they connect to can evenly distribute the power where it needs to go. You arent using it for that anymore, so youre best off just cutting the molex off and summing them on something metal and insulated as to avoid sparks etc, but still get the full amperage you can from the PSU. If you dont do this, youll run the risk of trying to pull too much current thru tiny ass wires and thereby heating them past the point where their shielding is designed to protect them at, it melting or burning, then FOOM, fire...

    Anyways, the deck needs +12v and gnd(which can also be obtained from the PSU) so does the amp. The deck will have a "constant" and a "switched" for +12v, and unless you plan on leaving the psu on at all times (HORRIBLE IDEA) youre going to run into the need of resetting your bass/treble etc etc if theyre digitally controlled inside the deck or find some alternate source of a tiny amount of +12v and a ground to maintain the internal memory on the deck and use the PSU for its main power."

    based on what I was told I had the doubt that perhaps a AWG8 cable (bigger) is not the ideal solution
     
Loading...