# Flickering LED light strip



## deefordog (Dec 31, 2013)

I recently installed a 1.5m LED strip (cut from a 5m length/roll) and wired it into the existing 'van 12v system via this switch http://www.diy.com/departments/bq-r...34_BQ&ef_id=VF1NTAAABMfulQt6:20141107225532:s

Recently, the strip has started flickering when it's been on for more than one hour. Given that these LED strips are only 5w per metre length, I should only be drawing c. 7.5w. In an attempt to sort out the flickering, it became apparent that the screw terminals in the switch are very hot to the touch. Given that the switch is rated at 2A, it should be able to handle at least 25-30w.

Any ideas why the switch contacts/terminals should be getting so hot as I think this may be causing the flickering?


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## gaspode (May 9, 2005)

My guess would be that it's because you're using a switch specifically designed for use with AC on DC instead. Apologies in advance but it's a bit of a technical explanation that follows.  

A switch rated at 2amps AC should be capable of switching a load of 500w on 240v AC, however using it on DC is a completely different story. On AC the current varies continuously with voltage and will become zero twice ever 50th of a second which means that at some time in the fraction of a second as your switch contacts open when switching off, the current will become zero and quench any arcing. This effectively prevents a sustained arc being created between the switch contacts.
On DC this doesn't happen because you're switching full current every time, which can cause considerable arcing across the contacts. This arcing will then burn into the contacts and create a resistance across them. The resistance thus created will then act as a heat source, making the switch warm, reducing the voltage being delivered to your load (the LED strip) and could possibly cause the flickering.
There is also a possible element of inductive load being switched which would also contribute to the arcing at switch off but maybe trying to explain that is going too far. It's why things like time switches are rated much lower for use with inductive loads such as low energy bulbs.

There are switches made specially for use with 12v DC which incorporate a "snap" action, better contacts and greater contact seperation which reduce the arcing to a minimum, maybe you need to try one of these switches?


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## listerdiesel (Aug 3, 2012)

Is it the whole string that is flickering, or just a couple of LED's ?

As Gaspode says, switch contacts may be the issue, but for what you are switching I'd have thought the switch would be OK. I'd try another strip before condemming the switch.

A failing LED that is pulling too much current would also affect the strip.

Unfortunately, many sub-standard LED arrays get onto the market. We have bought about 60 G4 round arrays in the past year or so, one batch had individual LED's flickering, which were replaced by the seller, another batch had colour casts on some.

Peter


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## gaspode (May 9, 2005)

> Unfortunately, many sub-standard LED arrays get onto the market.
> Peter


You're absolutely right there Peter, it could well be a fault on the LED strip. I simply based my answer on the fact that the O/P reports that the switch terminals are getting very hot - not something I would expect under the loading described.

When buying LED lamps of any description from sources such as Ebay you have to consider the price you're paying. Many of these items are sold at completely unrealistic prices so it's hardly surprising that many turn out to be faulty in some respect. In many cases, the items for sale cheap are just the ones which fail the QC procedure. They might work but they have some sort of fault. In my experience with LED strips it's often defects in the silicon layer which allows water to enter the workings over time causing eventual failure. I recently bought some 5630 strip from China at a price not much over £1 a metre 8O fully aware that there was some risk involved. In the event it turned out to have a very slight pink cast to the (white) light colour - not a problem to me as colour was not important for the intended use - but it just confirms that the strip probably failed the QC process although it was being sold as perfect.

Just goes to prove that there's no such thing as a free lunch (or even a cheap lunch) these days. If you want guaranteed quality and reliability you need to pay a realistic price.


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## deefordog (Dec 31, 2013)

Thanks guys for all your help and thoughts.

The strip in question does flicker as one for a few milli seconds at a time, not individual lamps. I had a thought this morning that perhaps the wiring was too thin as I used speaker/bell wire but then again the wires aren't getting hot. The flickering only occurs when the strip has been in use for a period of time, so I'll have to go along with Gaspode's reasoning that the switch isn't man enough for the job.

We have two other identical lengths which haven't given any problems yet but they're running through a dimmer switch and never at full illumination, so I guess the loadings are lower. I've checked the switch terminals on these two and they're cold after several hours of use.

I'll look to source some suitable 12v switches but they need to be similar in size to the AC ones due to the location and surface fixing - any ideas?


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## deefordog (Dec 31, 2013)

A thought - the obvious choice for a 12v switch would be an automotive toggle switch so Halfrauds or Maplins are on the cards today.


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## gaspode (May 9, 2005)

It's difficult to recommend a specific switch, only you can decide what would be acceptable cosmetically. Try looking in Halfords or Maplin for a switch rated for 12v DC at 5 amps or so. No doubt RS will have something suitable if you look through their website:
http://uk.rs-online.com/web/


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## listerdiesel (Aug 3, 2012)

Try replacing the switch, or put one of the other strips on it to try and pin it down.

Peter


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