Power adapter for 400 LEDs? The last one blew!

28 Dec 2008
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United Kingdom
Seasons greetings!

I have wired up, using multiple strands, what I would guess to be up to 400 LEDs - mostly around the garden, but some at the front of the house and some inside the house. (the strands originally came from cheap solar power garden string LEDs, but I removed the solar panels and connected the strands together to make a long chain. I don't believe the LEDs themselves are the 'super bright' LEDS available)

I used a £7 multi-voltage adapter, setting the voltage at 4.5v. It was a:
Lloytron 300mA Unregulated AC/DC Multivoltage Mains Adaptor Black A1506BK

Unfortunately, probably within an hour, the power adapter failed. Turning the power outlet wall switch off and on again got it working again, but the power adapter failed then even faster. Now, the power adapter won't turn back on at all. A red LED on the adapter also does no longer lights up.

Could you recommend to me a power adapter capable of:
-powering up to 400 LEDS (it might be less)

(and would a separate power breaker for the adapter be useful?)

And could I also ask, how best to get the power evenly distributed across the lights, so they don't start of brighter near the source, and practically dead near the end of the chain?

ALTERNATIVELY: Perhaps I should just buy 400 LEDS with a dedicated 230V adapter? Only £20!


in which case, would it be possible to branch off from this, near the power source, to power up to 30 LEDS that we have around the house?

Many thanks![/url]
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You need to calculate the current and voltage requirements for the LED, and base your adapter on the requirements ( taking into account the wire length and number of LED's!)
You really need to work out the current draw. A small super bright LED might typically be 10-30ma, so 400 could draw 12amps. If it's anywhere near that it's not surprising your PSU blew. Can you see any writing or numbers near the LEDs. Numbers such as 3630, 5050, 5630 or 7020. If you know what sort of LEDs they are you can find a power consumption.

A properly sized power supply might sort your problem of the LEDs further away being dimmer. Oththerwise you'll need to run a trunk cable of reasonable size wire and attach each set of LEDs to that, rather than daisy chaining them together.

As you say it might be easier to buy a new one with a properly sized PSU, although with LEDs the saying "you get what you pay for" is very true.
The LED is a current device not voltage so to power from a voltage source needs something adding to control current could be as simple as a resistor or as complex as a switched mode power supply.

As you add more and more LED's in series it becomes harder and harder to control the current. And colour does matter.

So a red LED rated at 30mA will likely have 1.2 volts across it. So 8 in series will need around 9.6 volt so with a 12 volt supply 2.4 volts / 30 mA = 80Ω but feed it with 14 volt then 147Ω. But with a single LED then 360Ω @ 12 volt and 427Ω @ 14 volt the difference is far smaller. Drop 30 mA to 20 mA and you will not see that much difference but drop 30 mA to 10 mA and they will be really dull.

Raise the voltage and you can clearly power more LED's on each string but 1 LED and the 360Ω resistor uses the same power as 8 with a 80Ω resistor so using a simple resistor you really need a stable supply voltage and multi sets of 8 LED's.

So lets say for example 50 sets then 1.5A as sets of 8 in series but as singles then 12A for same number of lamps.

Some LED's come with current regulation built in others don't and according to colour threshold voltage of 1.63 to 3.5 so if every one is 30 mA you would have to build a strip of say 5 and use a resistor then measure the current and adjust resistor size.

I have tried all sorts including using a 555 timer and over driving with pulses all good fun.

The 12 volt LED you buy may have a small chip to control current or a simple resistor which is why there are very different figures given on lumen per watt output.

You don't say exactly what you have so I can only guess why they failed. Likely either drawing too much or too little current.
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Basically, pretzelz, they aren't jjst lots of small bulbs which you can string together as if they were - a lot more knowledge of their nature and planning for their needs is needed.
Thank you all for your replies.

Since £20 on Ebay will give me around 400 LEDS and an appropriate power source, it looks like that will be the way to go, especially in light of christmas :)

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