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Thread: Power supplies for LED lighting

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    Default Power supplies for LED lighting

    I think that I have started to run up against the amperage limit of the 3A "wall wart" that I am using to power LEDs. This is a dedicated circuit supplying only a lighting bus, and the LEDs are hooked up in parallel with appropriate resistors in series with each LED. I have banks of LEDs controlled by switches so I can illuminate some but not all buildings, but notice that when they are all on there is noticeable dimming.

    Did I hook these up incorrectly? Should they be divided into several banks that are hooked up in series, or have I just reached the current limit?

    If so, what does everyone suggest for a dedicated LED power supply? Am I better off with several 1-3 amp wall warts, or one larger power supply providing more amps than I will ever need? Jameco has a load of different power supplies available, so there seem to be some good choice.

    For this application, what about switching vs. non-switching? Also, at what point do they need a cooling fan. Any advice would be appreciated.

    Thanks,

    Dan

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    Given that you have the bus already, it's likely easier to just switch to a single, larger power supply. If you go to multiple smaller wall warts, you have to worry about distinct buses for each plus having available outlets for each wart installed.
    Peter

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    It should work if you add another wall wart to the same bus. 3 amps plus 3 amps = 6 amps, right? Just be sure to get the polarity matched.

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    I use an MRC 1300 or 1370 connected to an MTH Terminal Block for all of my accessory lighting. Neither have failed me yet regardless of how many lights I have running, and I am referring here to my old HO layout.
    Cheers Tony

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    Quote Originally Posted by danb View Post
    I think that I have started to run up against the amperage limit of the 3A "wall wart" that I am using to power LEDs. This is a dedicated circuit supplying only a lighting bus, and the LEDs are hooked up in parallel with appropriate resistors in series with each LED. I have banks of LEDs controlled by switches so I can illuminate some but not all buildings, but notice that when they are all on there is noticeable dimming.

    Did I hook these up incorrectly? Should they be divided into several banks that are hooked up in series, or have I just reached the current limit?
    You hooked them up alright. How many LEDs at which current are you connecting? Or give us the voltage and resistor size...

    Becaue 3A = 3000mA, a typical LED will light up nicely somewhere between 2mA and 20mA, so you can connect between 150 and 1500 LEDs to a 3A power supply.

    Depending on the type of the power supply, the dimming may be a sign of coming close to the current limit - or a sign of a cheap wall wart with a non-stabilized output, meaning the output voltage will drop as the load increases even when you are far from the current limit. Or a sign of weak wiring... what gauge is your bus?

    Quote Originally Posted by danb View Post
    If so, what does everyone suggest for a dedicated LED power supply? Am I better off with several 1-3 amp wall warts, or one larger power supply providing more amps than I will ever need? Jameco has a load of different power supplies available, so there seem to be some good choice.
    Depends. Are your lights all close together, do you run all the power through a central control panel? Then go with a large power supply and heavy bus wire (as @pbechard suggested before me). Do you have your lights spread around the room with outlets conveniently located close to every cluster? Go with smaller power supplies and decentralized control panels.

    Quote Originally Posted by danb View Post
    For this application, what about switching vs. non-switching?
    Definitely switching. Are non-switching power supplies even available any more? Non-switching power supplies only make sense for very special use cases these days, like top-of-the-notch audio equipment or NIST-level measurement devices.

    I suggest go for a cheapo USB charger if it fits the bill - with the number of mobile phones available out there, they are among the cheapest reliable devices in the market (economies of scale...) and if you ever need to, you can power your lights from a powerbank

    Quote Originally Posted by danb View Post
    Also, at what point do they need a cooling fan. Any advice would be appreciated.
    It depends on the power supply, but generally speaking, switching power supplies don't need a cooling fan. Think of your laptop power supply, typically in the 100W-range (5A at 20V) - no cooling fan required.

    Quote Originally Posted by NtheBasement View Post
    It should work if you add another wall wart to the same bus. 3 amps plus 3 amps = 6 amps, right? Just be sure to get the polarity matched.
    If the wall warts have the exact same output voltage (including tolerance) and behave similarly when loaded, yes. If you connect a 4.8V power supply (5V -4%) to a 5.2V power supply (5V +4%), the 5.2V one will take all the load and even when no LEDs are connected there will be a lot of current flowing from the 5.2V supply to the 4.8V supply, which may damage either of them. Especially with modern switching power supplies, this can be critical, a traditional transformer-rectifier setup is more forgiving here.

    To be safe, connect each output through a decoupling diode to your bus - which will cost you about 0.6V: https://www.researchgate.net/post/Wh...es_actually_do (connect your power supply positive terminals to 3 and 4 and your bus to 1, the resistor is where your LEDs are). Still, if the output voltages are different, the one with the higher output voltage will provide most of the power.

    Heiko

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    Quote Originally Posted by Heiko View Post
    Depending on the type of the power supply, the dimming may be a sign of coming close to the current limit - or a sign of a cheap wall wart with a non-stabilized output, meaning the output voltage will drop as the load increases even when you are far from the current limit.
    This would be my first guess.

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    Oh, and I almost forgot: If you ever think of connecting the AC output of transformers in parallel, DON'T EVER. Because if you do and then pull the plug of one of them, there will be mains voltage at the open pins.

    With almost exclusively DC power supplies these days, that risk at least is a thing of the past.

    Heiko

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