i have an old project that is causing the client current problems. installed was 12v halogen lighting 10w bulbs,G4 base, multiple lights, buried cabling, multiple transformers from 120v to 12v. client is interested in swapping to LEDs and i understand the halogen transformers will not successfully run the LEDs due to flickering and burn-out issues. there are 7 different lines, in two distribution blocks, run by 2 transformers, 4 and 3... i am at a loss on how many transformers, resisters, etc. to use to power the "new" LED lighting...

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    \$\begingroup\$ Welcome to EE.SE. We appreciate proper punctuation, capitalisation of words and electrical units and spelling. It helps legibility and credibility. "i (sic) understand the halogen transformers will not successfully run the LEDs due to flickering and burn-out issues." Why would a transformer cause flickering? What burns out - the transformers or the LED lamps? \$\endgroup\$ – Transistor Sep 20 '17 at 19:37
  • \$\begingroup\$ Is it important that the lamps use 12 V, e.g. are the wires exposed? \$\endgroup\$ – Andrew Morton Sep 20 '17 at 19:37
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    \$\begingroup\$ You can get G4 LED bulbs that will run on AC - just look around and be careful not to buy DC-only ones. \$\endgroup\$ – user_1818839 Sep 20 '17 at 20:10
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    \$\begingroup\$ Are the original transformers real copper iron transformers, or electronic "transformers"? \$\endgroup\$ – Ian Bland Sep 20 '17 at 21:03

When I did this I used 4x 3W rated LEDs in series using only about 8W on an Alumclad thin strip for illuminating under each wood step and used a 30A Sh diode bridge and high ripple current rate cap >16V with no series resistors and the power was just right and not using all the LED rated power with no flicker. I think I had a 200W Schlumberger transformer. But this takes some skill with Ohm’s Law and pre-made 1*4” alum PCB with Cree LEDs. If you have similar 4S power LEDs on a board, you can try a test with a Bridge and 1mF low ESR cap and maybe a 1 or 2 ohm series R after the bridge.

You can also get outdoor coated power StripLeds which are less efficient since the 4th 3V drop is replaced by resistors for much wider voltage tolerance to 14.2V and power from a Bridge and 1mF low ESR cap per transformer

  • or consider these and save all the underground expense.

If you define the lighting , LEDs or luminaire, and power per drop, better solutions may exist.


i understand the halogen transformers will not successfully run the LEDs due to flickering and burn-out issues

If we're talking about oldskool transformers (the heavy ones) they output 12V AC at 50/60Hz so you need G4 bulbs that can take AC. They are easy to find, just check the specs. However notice a G4 bulb is quite small so there is not much room for a capacitor, which means they are probably going to flicker at 100/120 Hz. If this is a problem, get bulbs specified as flicker-free or read on.

If we're talking about "electronic transformers" (the flimsy and very light ones) they usually output 12V AC at a high frequency like 25 kHz or more which is usually also modulated by mains frequency. You need the same 12V AC LED bulbs, and they might flicker (or maybe not).

Some of these "electronic transformers" have a minimum load which might not be met by just a few LED bulbs, which then causes the electronics to misbehave and the light blinks or shuts off. I have some of these "transformers" in fixtures and usually they need at least one bulb to be incandescent.

If these "transformers" cause problems, a simpler solution is to replace them with 12V DC switching power supplies which are cheap and available. Then your G4 bulbs will get 12V DC and they won't flicker.


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