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Thread: Powering LED screw lights

  1. #1

    Default Powering LED screw lights

    Evening all I'm wanting to power four LED screw lights rated at 0.25w each which I'm going to wire in series would the below power adapter work for this purpose? Any help greatly appreciated.

    https://www.amazon.co.uk/Adaptor-Swi.../dp/B019RO949C

  2. #2
    Flashaholic* DIWdiver's Avatar
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    Default Re: Powering LED screw lights

    What voltage are the lights designed for? We need to know a lot more than just the wattage rating.

  3. #3
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    Default Re: Powering LED screw lights

    Quote Originally Posted by DIWdiver View Post
    What voltage are the lights designed for? We need to know a lot more than just the wattage rating.
    Yes, more info on lamps is needed. If they use simple resistive current limiting and (assuming they are white LED) if you use four in series, 12v supply may not be quite enough to light to full brightness, three might work.

    In general a voltage-regulated dc wallplug does not provide current regulation required by LEDs; not to say it can't be used under
    the right conditions. Adapter itself seems pretty ordinary, except the terminal block. I find 12v/1A regularly in 2nd-hand stores for $2 each over the counter.

    Even this is overkill for 1W worth of lamps. There exist very small 12v/0.25A adapters generally to charge batteries in equipment.

    I've been using small flange-based LED bulb replacements for years, they can work well. One variant is 1-2 cell which uses step-up
    circuit in the base. I would be careful putting these is series. Other 3-4 cell variant seems to only use a dropping resistor but higher
    input voltage requirements.


    Dave
    Last edited by Dave_H; 07-28-2019 at 08:53 AM.

  4. #4

    Default Re: Powering LED screw lights

    Hi thanks for the reply the LED's are rated at 12v.

  5. #5
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    Default Re: Powering LED screw lights

    Quote Originally Posted by mattm19 View Post
    Hi thanks for the reply the LED's are rated at 12v.
    Now I'm confused...

    12v 0.25W bulbs wired in series with a 12v supply is not going to work. Wiring in parallel
    should be OK assuming the bulbs have built-in current limiting.

    Even wiring four in parallel, the 12v 2A wall adapter is way overkill.

    Are these by chance automotive-type bulbs? Those contain series resistors and usually one or more
    series diodes for reverse-polarity protection.

    (Actually one which is sealed which I can't easily get apart, I can see contains a constant-current regulator
    which allows it to operate over 10-30v with constant brightness).

    Dave

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    Default Re: Powering LED screw lights

    Quote Originally Posted by Dave_H View Post

    Are these by chance automotive-type bulbs? Those contain series resistors and usually one or more
    series diodes for reverse-polarity protection.

    (Actually one which is sealed which I can't easily get apart, I can see contains a constant-current regulator
    which allows it to operate over 10-30v with constant brightness).

    Dave
    I mention this is due to interest in low-voltage, low-level LED lighting primarily designed for automotive use, which can run from 12v dc adapter or battery.

    Over several years I have acquired a variety of LED bulbs including older bayonet-base such as 1156/1157 type; likely similar to what you want to use. Other lamps are meant for hard-wiring into vehicle power. 12v 0.25W is about 20mA, typical for small 3-5mm or SMT LEDs.

    Most are not very efficient as they are connected as 3 series LEDs (or parallel groups of 3) run from 12-14v which is right off the bat, 50% or lower efficiency for red/yellow/amber; more so with some with only 1-2 in series such as "penny" style marker lights.

    What colour are your bulbs?

    Let me know if this is of not too off-topic, or I could make it a new thread.

    Dave

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