LED Lights Failing

jus001 · Jan 17, 2016

Hello,

I bought a couple of LED plinth lights and connected them up in parallel to a standard 12V switch mode power supply (measures a steady 12V) only to have one fail a few minutes after powering up and then the second one failing a few seconds later. A second pair did pretty much the same thing. They have a single SMD LED in them and appear to have a resistor built in.

Does anyone know why this might be happening please? I'm probably missing something really obvious but can't think what the problem might be at the moment!

Thanks,

J

Jay R · Jan 19, 2016

Perhaps they aren't 12 volt input lights ? They may be 5v input or such. Do you have the specs to hand ? Also, are you sure the + and - are the correct way around.

FRITZHID · Jan 19, 2016

LEDs are diodes, they won't function at all if polarity is reversed. My guess would be they aren't ment for 12v operation, OR if they are, they needed to be heatsinked. I'm betting if you'd touched them while running they'd have burnt you fairly nicely. Do you have a specs sheet on them to confirm proper operating voltage & application?

Jay R · Jan 20, 2016

FRITZHID said:
LEDs are diodes, they won't function at all if polarity is reversed.

Which would be true if the lights only had an LED and a resistor, however, there may be additional circuitry involved that the poster didn't notice which is why I mentioned it. Having said that, I also strongly suspect they aren't 12v led's and they are just burning out.

beley · Jan 20, 2016

Its also possible that they are meant to run on 12VAC, which with no extra circuitry would mean they would be running at 50% (or less) power they would be with 12VDC.

PhotonWrangler · Jan 20, 2016

That power supply might be putting out spikes that are greater than 12 volts. The only way to know whether this is happening is with a 'scope on the output.

jus001 · Jan 22, 2016

These are the lights:

http://www.strictlyleds.co.uk/30mm-led-plinth-deck-light-various-colour-options

They claim they are 12V and the supplier confirms that. It's hard to see inside properly but it doesn't look like there's much else other than the LED chips and a resistor.

I'll have a look at the output of the power supply on a scope and see if it's doing anything nasty.

Other than that I'm a bit stumped.

jillthomson · Mar 2, 2016

jus001 said:
Hello,

I bought a couple of LED plinth lights and connected them up in parallel to a standard 12V switch mode power supply (measures a steady 12V) only to have one fail a few minutes after powering up and then the second one failing a few seconds later. A second pair did pretty much the same thing. They have a single SMD LED in them and appear to have a resistor built in.

Does anyone know why this might be happening please? I'm probably missing something really obvious but can't think what the problem might be at the moment!

Thanks,

J

Biggest enemy of any LED is the heat they generate while operating, and if proper heat sinks are not attached with them (even low powered LED have a miniature size heat sink attached to them) then they can fail very quickly, so please check if the heat sinks are no0t too small and are getting proper ventilation...

DIWdiver · Mar 2, 2016

Those are assembled luminaires, not LEDs. There's no way to add any heatsinking to them. And the spec sheet clearly says they "can be run from any 12v DC power source".

Any switchmode supply should be regulated 12V and not be putting out spikes large enough to damage the LEDs. So it really doesn't look like you are doing anything wrong. I'd say check the power supply to see if it has failed and is putting out more than 12V, or is doing something unexpected. If not, it looks like you got a bad batch and should expect a refund.

Jay R · Mar 3, 2016

Pretty sure he was talking about the heat sinks inside the bulbs. If you don't have a good thermal path from the LED's to the case they will overheat and burn up pretty fast.

DIWdiver · Mar 3, 2016

That's true. But it that's what happened, it was a manufacturing defect, and he should get his money back.

LED Lights Failing

jus001

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Jay R

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FRITZHID

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Jay R

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beley

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PhotonWrangler

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jus001

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jillthomson

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DIWdiver

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Jay R

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DIWdiver

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