We've got 12V halogen G4 fixtures mounted under our kitchen cabinets and would like to use LED's instead. I found some G4 LED bulbs on Amazon, and they fit in the fixtures just fine, but if I try to replace more than one of the halogens with the LED's, they won't fire up (they just barely come on at all).
On a circuit with two fixtures, if I have one LED and one halogen, they light up just fine.
You probably need to replace the power supply with one designed for LEDs. According to various web sites, some LEDs have compatibility issues with transformers designed for halogens. In particular, the power supply may have a minimum load and your all-LED setup uses too few watts: "When replacing with LED bulbs they found they had to keep at least one halogen in the circuit to keep the load high."
Are all the fixtures connected to one ballast? In any case the the power supply or driver needs to be changed. You will need a driver that is rated in Current and voltage to match the number of lamps you connect to it. If you can share the current and voltage rating of the Led lamps purchased I can help you with that. Noor
@Foo Bar is probably right here but there are literally no givens are rules for LEDs right now. All manufacturers are spending ton of money on trying to get them to act just like incandescent bulbs and they certainly aren't sharing their technology or striving to use a certain "code".
I have actually contacted GE and another manufacturer to ask them a series of questions. Their answers were all over the place and sometimes different bulbs at same company had different answers and even worse sometimes the same (model) bulb had different specs.
My first reaction would be to try a different bulb. For instance there are certain LED dimming bulbs that have blinked when I place them with a certain type of switch (rated for LED of course), then I use another switch and they are fine. I have had dimming bulbs go nuts on certain dimmers and 3 different models later all is good. I know the manager at a local Lowe's and he said that LED bulbs were by far their biggest return. Other than "try a few things out before doing anything drastic" my other piece of advice is buy a few samples at a local store so you aren't paying shipping. You have to understand that these are simple electrical equations anymore since we are no relying on complicated chips inside of the LEDs.