2 power supply one common/negative possible

Discussion in 'Power Electronics' started by Maldives, Dec 25, 2017.

  1. Maldives

    Thread Starter New Member

    Dec 16, 2017
    6
    0
    Hi,

    I am building 100W studio led light and I have 2 power supply I am planing to run 3 pin jack to light
    wire 1 12v for fan
    wire 2 26v for led
    wire 3 Negative

    Is this possible?
    Screen Shot 2017-12-25 at 9.50.18 PM.png
     
  2. ian field

    AAC Fanatic!

    Oct 27, 2012
    6,172
    1,115
    It depends on the PSUs - if one has a floating output; you're in the clear.

    Its not unusual for the negative terminal to be a chassis connection, which is also OK.

    If one of them is positive earth - there will be problems.
     
  3. ElectricSpidey

    Member

    Dec 2, 2017
    443
    95
    Just calculate the current needed for the fan and use either a power resistor or a regulator to run the fan from the 26/36 volt supply. (your text does not match the diagram)

    You could get a small PWM controller and just use that right at the fan.

    I mean if you are going to use a power supply…you might as well just step down instead.
     
  4. Maldives

    Thread Starter New Member

    Dec 16, 2017
    6
    0
    Thanks,

    I am planing to have a common power supply and use multiple lights each have 12v fan and 32v led.
    whats is the best option:
    1. have a common voltage step down for 12v in 32v power supply and wire 3 wires to light
    2. wire 2 wires to light and in each light use resister or voltage step down for 12v
    3. have 2 PSU and wire 3 wire to light with one common (as above)
    12v https://www.meanwell.co.uk/s-40-15.html
    32v https://www.meanwell-web.com/en-gb/ac-dc-enclosed-power-supply-output-48vdc-at-10a-sp--500--48

    is this PSU can be used if so how?
     
  5. Audioguru

    Expert

    Dec 20, 2007
    10,399
    1,140
    How will you limit its current and cool the LED? Please post its datasheet.
     
  6. Maldives

    Thread Starter New Member

    Dec 16, 2017
    6
    0
    I am very new, Planing to to have step down with a knob to limit voltage and using 2 CPU heatsinks and fan

    Specification(20w/30w/50w/100w)
    Model Type: High Power Integrated Chip lamp Beads
    Chip size: 24MIL*44MIL
    Forward Voltage: 30-36V
    Forward current: 20w(600mA) 30w(900mA) 50w(1500mA) 100w(3000mA)
    Luminous Flux: 90-120LM/W
    Color-rendering index: 60-85
    Beam Angle: 120 degrees
    Working Temperature: -20 centigrade to 60 centigrade
    Color Temperature: Warm White: 3000-3200K
    White: 6000-6500K
    Life Span: 100,000 Hours
     
  7. Audioguru

    Expert

    Dec 20, 2007
    10,399
    1,140
    Each LED has a different forward voltage that changes a little when it warms up.
    You do not "step down" the voltage to change the power in an LED, instead you reduce its current and its voltage stays almost the same.
    Pulse-Width-Modulation (PWM) is usually used to adjust the power of powerful LEDs.
     
  8. ElectricSpidey

    Member

    Dec 2, 2017
    443
    95
    Have you bought the parts yet?

    Try to spell out exactly what you need in the end.

    And I’m confused, you state 3 different voltages for the higher supply.
     
  9. Maldives

    Thread Starter New Member

    Dec 16, 2017
    6
    0
    Sorry
    I have 2 PSU
    https://www.meanwell.co.uk/s-40-15.html
    https://www.meanwell-web.com/en-gb/ac-dc-enclosed-power-supply-output-48vdc-at-10a-sp--500--48

    I want make 2 or 3 100W LED studio lights(dimmable and data sheet above) with a common power supply.

    Each led light have a CPU fan with a heatsink

    what is the best way to go forward I don't mind having single PSU

    Thanks
     
  10. Audioguru

    Expert

    Dec 20, 2007
    10,399
    1,140
    The 15V power supply is not 12V. Use a 12V power supply to run the 12V fan.
    The 48V power supply has a voltage that is too high and it does not have adjustable current. Use a power supply that is made to vary the power in your LEDs.
     
  11. ElectricSpidey

    Member

    Dec 2, 2017
    443
    95
    You could turn that 15 volt supply down to 13.5 and run those fans, when a fan is rated 12 volts that is usually a nominal voltage, and another 1.5 won’t hurt. Or use a resistor if you are nervous about using 13.5. Wouldn’t need to be that big to drop 1.5 volts.

    You could also run 4 12 volt fans from the 48 volt supply in series. No need to change their speed when you dim the LEDs.

    The real issue here is why do you need to use only 3 wires…just use 4.

    But as the guru states you should use a current controlled LED driver for the lamps. (dimmable) Fiddling around with PWM and resistors is fine for lower power LEDs but I wouldn’t mess around with 100 watters. And be damn sure you can dissipate the heat from those bad boys.

    But it would be possible to run them off of that supply using a dropping resistor and a well heat sunk regulator in CC mode.

    If fact if you didn't really need to dim, you could just use a resistor, that would be risky if your heat dissipation is marginal.
     
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