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Thread: Electrical for dummies... Can you step down a PSU?

  1. #1
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    Question Electrical for dummies... Can you step down a PSU?

    I have a meanwell 24 volt, 25amp power supply. I was wondering if I could step the voltage down to something lower? If this is the right terms I am using. Can something like this be useful for a projector? I got it to power a 437W (I think) TEC waterblock for CPU cooling. Now it is just sitting in my room collecting dust. I wnat to know if I can use it with something laser related.
    Love, peace, and grease,

    allthat... aka: aaron@pangolin

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    Not a problem, just add linear regulators for each gadget to be supplied. If you want to be efficient (wise) buy some DC-DC converters to take 24V input and put out the current and voltage you need. At some point you'll need to separate any power supply into different voltages and current lines at need, and this big PSU will give you an extra stage of efficient regulation that will help to protect your gear. AND give you a low volt main buss, a nice safety feature.


    Edit:
    When calculating your safe limits for power and current, it's easy. Two basic rules:
    1. Linear regulators: Current in ALWAYS equals current out. The difference in voltage is proportional to waste heat. Big expensive heatsinks will be needed.
    2. DC-DC power converters are efficient! Very little waste heat, but POWER is equal both sides, so output voltage and input current rise or fall together as output voltage shifts from 24V.

    Those two rules will let you calculate your maximum current, up to 25A max. Aim slightly short of that to be safe, DC-DC converters always waste a tiny bit of energy.
    Last edited by The_Doctor; 09-29-2007 at 03:52.

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    Cool! Thanks man. As long as I don't need any Russkee capactiors... Sorry could help myself.

    I was worried I didn't have a use for this thing. It is kinda big though. Probably as long as the width of my projector. Now that I look at it it is a unipower corp not a meanwell.

    Um, since I'm a self proclamed dumb ass, you wouldn't happen to have a few links to what you are talking aobut.

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    What do you want to power with it? LDs? Galvos?
    You could power a row of laser sidewalk lights around your house

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    Quote Originally Posted by steve-o View Post
    What do you want to power with it? LDs? Galvos?
    You could power a row of laser sidewalk lights around your house
    Is it that big of a power supply? I dream of a 2 scanner projector, one rgb/ilda and one g or gyor/dmx...

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    25 Amps is a fairly hefty supply. Stepped down, it would power 69 Maxyzmodules!

  7. #7

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    Yes, 25A x 24V = 600W.

    That's not too much for a big projector, not really much more than most current computer PSU's put out. Thing is, most low-volt stuff is made to run off 12V or 5V so you might be better off using a computer PSU as they make those outputs already.

    If you want to look up linear regulators and DC-DC converters, it's best to google for links, they vary so much in detail and complexity, and the best thing to do is try a few that look like you can get a grip on them. No way to know which those are till you go hunting...

    Edit: What you really need to check out is Ohm's Law. Once you suss that out my first post will be clear. The power equation is called Watts law but it works the same way.
    Ohm's Law: Volts = Amps x Ohms.
    Watts Law: Watts = Volts x Amps. (I used this at the top of this post..)
    So you can shortcut that to get any ONE value from any TWO others, like Amps x Amps x Ohms will give you Watts...
    If you try that on a few knows examples you'll get the idea fast, and be able to apply it to regulators.
    Last edited by The_Doctor; 09-29-2007 at 07:56.

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    Since this is a switching power supply, if you only want to step it down a small bit, say to 18-20V, you could modify the feedback regulator in the secondary. This would keep high efficiency and you wouldn't need a big heatsink for a linear postregulator. This would require some knowlege of switching power supplies, though...

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    Lightbulb

    Quote Originally Posted by drlava View Post
    Since this is a switching power supply, if you only want to step it down a small bit, say to 18-20V, you could modify the feedback regulator in the secondary. This would keep high efficiency and you wouldn't need a big heatsink for a linear postregulator. This would require some knowlege of switching power supplies, though...
    Thanks man! Nice to see ya. I'd like to use it to power the whole projector so I would need several "rails", 5V, 12V, 15V, and probably 24V... Can I get 24+ and 24- like this?

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    Quote Originally Posted by allthatwhichis View Post
    Thanks man! Nice to see ya. I'd like to use it to power the whole projector so I would need several "rails", 5V, 12V, 15V, and probably 24V... Can I get 24+ and 24- like this?
    Nope, sorry. Only 1 Voltage. sounds like you're best off using postregulators. To make dirty -24V, you can use a charge pump voltage inverter if you don't need much current, otherwise it's another power supply for u.

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