I am new to this site and a little desperate too as I am no electrician. I purchased some led lamps (3w, 12V) to replace a series of G4 20w lamps I run in my household. Since the wiring is in the wall I would like to leave current configuration and just replace the current power supply and the current lamps to LEDs.

My problem is that I am uncertain of the power supply required to run 5 led lamps as shown in the diagram below. This is how currently everything is wired and I think lamps are in parallel?. Sorry but as stated earlier I am no expert! Can anyone help me?

Schematic of current wiring Led lamp specifics

Thanks and regards,


  • 1
    \$\begingroup\$ Do you have a data sheet for the LEDs or any link? \$\endgroup\$
    – Andy aka
    Dec 4, 2014 at 8:14
  • \$\begingroup\$ You say you are replacing a number of G4 20W (incandescent I assume) lamps. Those are 12v already, not? I would think you can just replace the bulbs with the LED ones and you're done. \$\endgroup\$
    – RJR
    Dec 4, 2014 at 8:41
  • \$\begingroup\$ Actually - you'll want to check if the current power supply gives you AC or DC. If it's an 'old' (heavy, with transformer) one it is likely AC. Newer ones (swhiched-mode, much ligher) are probably DC. Best way to check is with a multimeter in DC mode (12V AC should give about 0V). \$\endgroup\$
    – RJR
    Dec 4, 2014 at 8:49
  • 1
    \$\begingroup\$ What Raivis said - it's OK if the wattage of the power supply is higher than the wattage of the bulbs. Voltage should be 12V. connect as per your diagram. Note that bulb is probably polarity sensitive. \$\endgroup\$
    – Russell McMahon
    Dec 4, 2014 at 11:28

1 Answer 1


12V marking on your lamps imply they require regulated voltage, so you need 12V supply. You have 5x3W laps, that in total is 15W, hence you need power supply that can handle more than 15W, say 20W, so that there is some safety margin, which expressed in amps would be 20W/12V = 1.6(6)A, or in nice round numbers - 2A or more.
So answer is 12V 2A power supply is what you need. And yes, you have to connect them in parallel.


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