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I want to connect about 9 LEDs (12V DC) using a simple wiring. For that I prefer serial wiring.

But when I connect the LEDs in serial they don't working. When I connect in parallel, they are working.

The adapter output is 60w. What am I doing wrong? What can I do better?

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  • Each LED has a voltage drop. So you may simply not have enough voltage to get "through" all the LEDs in serial. Also keep in mind that serial wiring means "one dead, all dead" so parallel is generally preferred for lighting.
    – manassehkatz-Moving 2 Codidact
    Commented Apr 29, 2019 at 16:34
  • Will another transformeter solve the issue? What am I need to look for to find a UL that will support at least 3 pieces of 4V DC LEDs?
    – Aminadav Glickshtein
    Commented Apr 29, 2019 at 16:37
  • If each unit needs 4V, then a 12V circuit can only run 3 in series. You'd need a 36V power source to run 9 of them in series. This is getting towards the edge of what most places consider 'low voltage'.
    – Joe
    Commented Apr 29, 2019 at 17:19
  • @manassehkatz: LEDs often fail short circuit, so "one dead all dead" isn't always true, and in parallel, if one fails as such, all the energy will go into that one LED, until it re-fails open-circuit, and then the missing current is distributed to the other LEDs, pushing them harder and hotter than designed. once the 2nd parallel LED goes, the rest will instantly pop and you've lost the whole chain instead of one LED. this is assuming a traditional constant-voltage supply, like we use for tungsten. a constant-current driver will step down the voltage as LEDs fail.
    – dandavis
    Commented Apr 29, 2019 at 20:23
  • Not sure why the down vote not everyone understands solid state electronics.
    – Ed Beal
    Commented May 31, 2021 at 3:13

2 Answers 2

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I'm making some assumptions, please add the make and model of the LED-bulb and the power supply to the question. Assuming that you have LED 12V GU4 LED bulbs and some generic 12V electronic halogen (or 12V LED) transformer series connection of LED-bulbs is not possible.

It looks like you have a constant voltage setup, 12V power supply 1 or more 12V led bulbs. In this setup all LED-bulbs need to be connected in parallel and the voltage output of the power supply must match the bulbs. There is no reliable way to run multiple LED-bulbs in series even if the voltage of the power supply would be enough to cover the voltage drop of all bulbs.

There is however constant current setup, where all LED's must be connected in series. To explore this alternative search for LED bulbs or modules explicitly stating "constant current" or "driverless" in their description and then getting a constant current LED-driver with same or lower output current than the light sources chosen. The combined voltage drop of the LED's must be also in the driver's output voltage range.

Example for constant current setup: Parts picked somewhat randomly around Internet. Better combinations can be found.

That driver can drive 2 of those led modules in series. Only 1 module -- voltage drop is 11V which is less than 16V, 3 modules voltage drop 33V which is more than 32V. Also the LED-modules need to be attached to a heatsink to prevent them from burning out.

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It doesn't matter how you prefer to wire them. You must wire them in a way that matches the devices to the power supply.

If they are "dumb" resistor-limited units, and they are an identical match, then it's easy - hook 2 in series to a 24V supply instead of 12V. Or 3 in series to 36V, but that's the end of the road - any higher and you lose the low-voltage exemption, and you need to treat DC with the kind of fear and respect you ought to treat 10 times the AC voltage. It's a nasty customer. Do not mess with that unless you really know what you're doing.

If they have an internal DC-DC converter or constant-current regulator, then you cannot wire them in series. You must wire them in parallel at any of their spec voltages.

If you are driving bare LED emitter components, such as those made by Cree, where the spec sheet saysto drive them at a constant current... Then series connection is the preferred way to do it, since one CC supply can drive several emitters.

If you are hooking up LED products in series because you read the last paragraph somewhere, then read more :)

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