Kitchen counter LEDS are faulty- uniformly dim

[Manyprojects]

Hi all,

First post here! But no doubt there’ll be a few more…

I searched but couldn’t find anything similar to this answered before.

We live in a new build (2012) block of flats - in the kitchen there are low voltage kitchen counter/shelf LEDs, numbering about 10 (it varies slightly by flat size) connected to a transformer hidden behind an access panel behind one the of cupboard backs. The lights are switched on via a standard (ie not dimmable) light switch.

My neighbours lights have recently gone uniformly dim, and I offered to have a look.

First visit- found the transformer, checked there weren’t any loose connections and checked the output from the transformer at 43v.

I guessed the transformer was at fault after 12 years of service so I bought an identical one.

Second visit- replaced the transformer and… exactly the same, all LEDs are uniformly dim. The transformer is plugged into a standard three pin socket, so I tried plugging it into another of the sockets on the kitchen, no change.

So what’s going on? The transformer doesn’t appear to have been the issue. My neighbour said the LEDs flickered a bit and went bright before going dim, which suggested some sort of power surge but I find that unlikely through a transformer.

Assuming there was a power surge, is it possible it could have damaged the LEDs in a uniform way? They’re all the same level of (not very) brightness. Is there a way I can test them?

Oddly the LEDs appear to be wired up in series which I wasn’t expecting, as removing any of the led plugs turns them all off.

Photos attached of transformers (original transformer below and replacement above) and plug/wiring behind access panel.

Any comments or suggestions gratefully received.

Cheers

 

[Alec_t]

Welcome to DIYnot.

Oddly the LEDs appear to be wired up in series

That is quite normal for LED lights. The 'transformer' is actually a constant-current (350mA) driver with a maximum output of 43V. So if each light is rated for 350mA at, say, 4V the transformer could drive a string of ten lights in series (10 x 4V = 40V, leaving 3V 'spare').
I can't explain why the DC-driven LEDs are uniformly dim but all still light up.

 

[DetlefSchmitz]

Although I've never personally come across series connected leds, when they are connected that way, I suppose it is possible for a fault on one to make them all dim.

 

[Manyprojects]

Welcome to DIYnot.

That is quite normal for LED lights. The 'transformer' is actually a constant-current (350mA) driver with a maximum output of 43V. So if each light is rated for 350mA at, say, 4V the transformer could drive a string of ten lights in series (10 x 4V = 40V, leaving 3V 'spare').

Thanks- we’re about to buy a house that needs some work, so I expect I’ll be posting more quite soon…

Ok, that explanation of constant current makes sense.

Cheers

 

[Manyprojects]

Although I've never personally come across series connected leds, when they are connected that way, I suppose it is possible for a fault on one to make them all dim.

I thought that, but they’re all a uniform dimness.

I suppose it’s not beyond the realms of possibility that there could be a fault with one that makes it dim and somehow makes the others as dim - as they’re all wired in series and removing any plug makes them all go off I’d need to do some labelling and careful re-plugging together to find the faulty one.

Assuming I find one that is faulty, can I bridge the connector for that one on the distribution board, meaning that the remaining 9 are wired in series and the fault one is just left disconnected?

As the LEDs are glued into the bottom of the shelves with the wires (presumably) exiting through a hole drilled horizontally through the shelf I can’t imagine being able to extract one to replace it without wrecking something.

Cheers

 

[DetlefSchmitz]

Assuming I find one that is faulty, can I bridge the connector for that one on the distribution board

I would think so. In fact it may be a quick way to diagnose which lamp may be faulty.

 

[Alec_t]

Agreed. Whether 9 or 10 are in series should make no difference to a constant-current driver.

 

[SUNRAY]

The reason you are seeing 43V and dim lights is somewhere in the system there is insufficient load to draw the full 350mA (as would be the case if too many leds wired in series), you may very well find that shorting out any of the lights brings the rest up to full brightness.

One of the things that gets forgotten is LEDs age and gradually drawing less current means they are not as bright, this could possibly be the case here but I'm not trying to say it is.

I have a number of stage lights which are predominantly three 10mm LEDs in series with a resistor, as they are running right up to their limits failures are not uncommon.
These are some I purchased off Ebay last year as faulty, all should be lit but failures are obvious. Bottom left circled it may be possible to see 2 blues are dim where they have aged.

It's very difficult to take meaningful pictures

After the pic I repaired them and the replacement LEDs clearly show brighter.

 

[Doug99]

Using a new serviceable LED, swap each one in turn until you find the one causing the voltage drop.

Edit - That assumes only one LED is at fault. If 2 are at fault, the dimness should improve when one defective LED is replaced.