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Thread: Electronics Idiot here....

  1. #1
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    Default Electronics Idiot here....

    O.k., I'll admit it. I know less than I thought I did and am not too proud to display my stupidity. I keep getting parts arriving in the mail and end up saying... huh?? I've currently got two dumb questions as it pertains to power supplies. (More stupid questions will be revealed as we get into flexmods, scanners and DZ's colorboard!)

    1) I got a benchtop style power supply (photo below). I was always under the impression that, with something like this, you turned the voltage knob up to adjust the voltage and then adjusted the current knob in order to adjust the mA going to a particular device that you had connected. I assumed I could set the voltage to say, 5 volts and then, turn up the current knob to say, 500mA for the puposes of testing and measuring the output of a diode harvested from sleds. Then, perhaps adjust it to 550mA and re-check. Well.... it's strange. Apparently it doesn't quite work like that.

    One member said I need to adjust the voltage, then "short it out" (whatever that means - I guess connect the positive and negative leads together) then adjust the current reading to a point you want to test, and then turn off the power supply. Then, connect the diode and flip the supply back on. I guess I'm just not clear on how you stick a diode into a O-Like housing, attach some leads and then apply power to check it.

    2) Since a benchtop supply is obviously not what's used in a projector and it was suggested I buy 5 volt DC power supplies, I order four of the supplies in the picture that, again, hopefully appears below. With there being five wires, and a pot, I'm just not certain what gets hooked up to what. I'm guessing the red and black are going to be my AC current in from the wall. Then the white and black probably go to the laser driver. Not sure about the green and yellow wire though.

    I'd really like to not fry any expensive parts or myself in the process.
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  2. #2
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    Quote Originally Posted by Bradfo69 View Post
    I'd really like to not fry any expensive parts or myself in the process.
    Hehe...

    I'm a self confessed electrical 'numpty' (as we say in the UK). Like yourself, I don't really get the 'shorting out' bit and am looking forward to the explanations.

    I just thought it would be nice for you to know you're not alone. Just look upon frying some expensive parts as a sort of initiation ceremony, i've fried plenty

    Cheers

    Jem
    Quote: "There is a theory which states that if ever, for any reason, anyone discovers what exactly the Universe is for and why it is here it will instantly disappear and be replaced by something even more bizarre and inexplicable. There is another that states that this has already happened.... Douglas Adams 1952 - 2001

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    black and white are your AC in...

    black = hot
    white = neutral
    green = ground

    red + output
    black - output

    pot is probably a voltage adjust...

    most power supplies are not current limiting, they will put out whatever you pull up to their rating

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    Thanks Frank.... I would have definately had that one backwards. Although... upon thinking about it, that makes sense.

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    Quote Originally Posted by Bradfo69 View Post
    1) I got a benchtop style power supply (photo below). I was always under the impression that, with something like this, you turned the voltage knob up to adjust the voltage and then adjusted the current knob in order to adjust the mA going to a particular device that you had connected. I assumed I could set the voltage to say, 5 volts and then, turn up the current knob to say, 500mA for the puposes of testing and measuring the output of a diode harvested from sleds. Then, perhaps adjust it to 550mA and re-check. Well.... it's strange. Apparently it doesn't quite work like that.
    You can't adjust current without a load, only voltage (No load = no current )

    Quote Originally Posted by Bradfo69 View Post
    One member said I need to adjust the voltage, then "short it out" (whatever that means - I guess connect the positive and negative leads together) then adjust the current reading to a point you want to test, and then turn off the power supply. Then, connect the diode and flip the supply back on. I guess I'm just not clear on how you stick a diode into a O-Like housing, attach some leads and then apply power to check it.
    That would be me. Short it out = Connect positive and negative leads. This will give you a load, and the current limit can now be adjusted. Don't use too much time adjusting, or your power supply will overheat. <15 sec should be fine.

    Simple as that

    /Thomas

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    Quote Originally Posted by Badpip View Post
    You can't adjust current without a load, only voltage (No load = no current )
    That would be me. Short it out = Connect positive and negative leads. This will give you a load, and the current limit can now be adjusted. Don't use too much time adjusting, or your power supply will overheat. <15 sec should be fine.

    Simple as that

    /Thomas
    Wouldn't a small value resistor be better?

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    Quote Originally Posted by laser_freak View Post
    Wouldn't a small value resistor be better?
    A couple of diodes in series would be better, but it isn't necessary... Lab supplies are short circuit protected, so they will tolerate a LOT of abuse (Mine is still alive after 20+ years).

    Turn the current adjustment all the way down, short the output, and turn the current up to desired level. Doesn't take more than a few seconds.

    /Thomas

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