0

enter image description here

I have LED strip lighting under my cabinets in the kitchen. Recently, they started flickering with noise. Worked fine for a couple of years. I believe it was the adapter that was faulty. Unfortunately, I lost the adapter somewhere so I'm unable to order another without knowing how much wattage should it have.

My LED strip configuration is: 3528 (18/foot). I have 11 feet of strip. I know the wattage would depend upon the lumen.

Here are my queries:

  1. Am I right that the adapter caused the flickering and the noise or it could be the LEDs? (My previous experience with LEDs is that if they failed, all of them fail)
  2. Is there an average rating that I can use to determine the total wattage for the adapter? I have come across 0.08-1W on the internet
  • you can use a higher wattage (current really) adapter than you used to have w/o problems, just don't go lower. – dandavis Oct 16 '19 at 16:42
1

Your LED strip has one resistor per 3 LEDs, which is the standard for a 12V strip. Each group of 3 LEDs is wired in series, with the resistor setting the appropriate current. All groups of 3 LEDs plus resistors are then wired in parallel.

White LEDs take about 3-3.6V each, so 3 in series mean 9-10.8V, with the resistor taking the rest of the voltage up to 12V.

For a strip, the resistors set the current, so you don't need a constant current driver. You need a standard 12V constant voltage power supply.

3528 LEDs should run at about 20mA each, but remember they are wired in series in groups of 3, so each group of 3 LEDs will use 20mA on your 12V supply. So, 18 LEDs/foot means 120mA/foot, so 1.3 Amps total or 16 Watts.

If you don't fancy getting electrocuted, an enclosed power supply is better than an open frame or naked PCB. I like Meanwell so I'll shill for it. They also make IP68 waterproof models.

If you have a 12V DC wall wart lying around somewhere, that can also work well.

Am I right that the adapter caused the flickering and the noise or it could be the LEDs?

If a group of 3 LEDs fail on the strip, perhaps one LED is dead in that group, or a solder joint cracked.

If one half of the strip fails but the rest works, then the copper trace which carries 12V is broken somewhere around the transition between "works" and "doesn't work."

If all the LEDs are off, or all blinking, then it's either the power supply, wires, or connection between wires and strip.

(My previous experience with LEDs is that if they failed, all of them fail)

If they are all wired in series like in some lightbulbs then yes, one single LED failing open will open the whole circuit, but this is not how strips are wired.

2

Flickering is caused by the voltage conversion “driver” The driver sets the correct voltage and current level. The problem with today’s led’s Is they can be just about any voltage. For instance I have some 4’ strips that fire at ~40v but need ~60v for full brightness, so you really need to find the specs to get the proper driver for your lights. But yes flickering is a sign of the driver overheating and or starting to fail. I did look closer at your strips and they show 12v so then you would need a supply large enough in watts or amps at 12vdc to light them up.

  • I used to have a 12V adapter, but I'm missing the current. 5A would mean a 60W output. – Rohan Oct 15 '19 at 18:54
  • 1
    Yes 5 amp at 12v = 60W – Ed Beal Oct 15 '19 at 20:46
1

Unfortunately 3528 is simply an industry standard package name. It means the LED components are 3.5 by 2.8 mm with a specific "footprint" that describes where the terminals and solder should go on a printed circuit board.

We can see in your photo that the polarity and voltage are specified and there are markings where the tape could be cut. There are three LEDs and one resistor (the black component) in each section. That makes sense: white LEDs often have a forward voltage around 3.4. Three of them in series should require 10.2 volts; the resistor performs the role of limiting the current. A regulated 12V supply is all you'll need. The supply doesn't need to control the current for this type of LED tape.

As to the current or wattage capacity you'll need.. If you have an ammeter you could measure the current drawn by one or more sections and multiply up to accommodate the whole setup -- if not, then make a guess. This site claims LEDs in the 3528 package are typically operated about 20 mA per series string.

You mentioned your strip has 18 LEDs per foot. We see they're in groups of 3, so there are 18/3=6 groups, or series strings, per foot. Then each foot of tape might need 20*6=120 mA, and the whole 11 feet would need 120*11=1320 mA=1.3 amps.

Get at least a 2 amp (24 watt) supply and you should be fine.

1

This appears to be a fairly standard monochrome LED strip using 3528s. And I apologize, but I'm going to use Metric units because that's how they're specced.

  • The standard/common strip has 300 LEDs per 5 metres. This comes down to 3 LED per 2" segment. There are double density (600/5m) or half-density (150/5m) strips also.
  • This one is a "standard 300" using 3528s. Of these types:
    • A full 5 metre (16 foot) strip of these uses 24 watts per channel. It has 1 channel, being a monochrome strip.
    • As you might infer, that is 1.5 watts per foot.

Wow, that was easier than I expected.

As always, when dealing with Chinese stuff, you should overspec your power supply by a factor of 2 or 3. So if you figure out 20 watts, get a 50-60W unit. Meanwell is a good brand that you can drive closer to spec.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.