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LED Lights and Transformer


By Dave Rongey - Summary:

How to Install Electrical Wiring for LED Light Fixtures

How to Install Electrical Wiring for LED Lights

Electrical Question: I just bought a led spot light MR16 12volt to change them with the old one I had which was a spot light MR16 12volt. The replacement lamp is not working ? Do I need to get a different transformer for the led lights?

This electrical question came from: Giacomo, from London, UK

See more about Home Wiring in the UK

Dave’s Reply:
Thanks for your electrical question Giacomo

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2 Responses to “LED Lights and Transformer”
  1. Dave Rongey says:

    Hi Zach,
    Here is what I believe you have identified about LED lights: LED lights work with DC voltage and they are polarity sensitive because they are basically a diode which only allows voltage to flow in one direction. This is why they worked when you tested them with standard DC batteries and the polarity was correct. From what you have described, the power supply is the problem because it does not have a DC output. The oscillating output of the power supply will not work with the LED lights. The ma is simply the amount of power that will be required and consumed by each LED light, therefore the new DC power supply must be rated for at least the combined total of ma required for the number of LED lights that will be connected.
    I hope this helps,
    Dave

  2. zach says:

    One of my Christmas inflatable’s light wire pulled apart from the terminals, and at the time I didn’t have a way to fix them so I just threw the three LEDs away. I now am trying to wire 3 white LEDs in Series to my inflatable to get it to light up. I initially hooked up 9 incandescent to the blower motor and had problems with it working, although the light would glow dim it was not my desired effect. So, not knowing anything about LEDs I cut a string of LED lights that I bought and wired 9 up in series and tired to get them to work. As you guys probably know, there wasnt enough volts to light them. I then did research and found that my inflatable had a 12v adapter and I figured I had picked to many LEDs to light. I then tried to light 3 LEDs and that did not work. Thinking that the LEDs were burnt out I made a LED tester from 2 AA batteries and found that all my LEDs worked. I did even more research and found that LEDs have to be hooked up a certain way to work and can not be run in reverse polarity.

    With all this new knowledge I thought I had figured it out. I ran my lights and thinking my lights were rated for 3.4v I figured 12v would be plenty to run 3 of these LEDs and not t much to make them burn out. Well I plugged them in and still no light.

    Here is the information I have so far:

    The string was 50 mini LED warm white lights. The string is rated 4.8 watts (.04amp). The lamps are to be replaced with 3.8v .076watt LED only. That converts to 5.6ma per LED.

    I checked each of my LEDs with my 2 battery LED tester and they all glow. What I have found now is my DC power supply is alternating volts from 8 to 11 and back again. I think my Power Supply may be bad. My latest test was like this. ” I Plugged in my power supply. Tested the volts and got 12.24v. Connected my string of 3 warm white LEDs at that are rated for 3.8v, and nothing happened. I checked my voltage from the beginning of the string to the end of the string and got 12.24v. Scratched my head and asked my self “Shouldn’t I have had some sort of power drop through the whole string?” I am not sure but I think I should have. I tested again and the Volts started alternating. I checked my outlet and was getting a steady 116v.

    Why is it people say 20ma across the LEDs and these are needing 5.6ma? Can to much amps cause them not to light up?