Help! Why the flicker?

[Bill Gardener]

Further to my post below I still cannot find the reason for my halogen LV lighting flicker.

The LV lighting consists of two 150W 12V transformers:

?id=10483&ts=12289Each supplying three 50W lamps:

?id=13423&ts=12289I checked the entire lighting circuit for a loose connection but couldn't find one. So I temporarily removed the transformers from the lighting circuit and connected them to a 13amp plug. After plugging in to the nearest socket the flicker was still there so I assume this rules out a fault on the lighting circuit.

Also I have noticed that when first switched on the lamps are fine, the flicker only develops after 10 minutes or so.

In my mind this leaves one of three possibilities:

1. There is a fault that affects all circuits in the house. Maybe at the consumer unit.

1. The transformers are causing the flicker.

2. All the lamps are faulty or they are incompatible with the transformers.

I am reluctant to buy replacement transformers/lamps and I am a bit stuck on how to proceed from here.

Any thoughts/advice would be most appreciated.

Thanks,

Bill

[Sparks]

Although the transformer is rated at 150w and the total wattage of the lights is also 150w there is always some loss, so you may find your transformers are getting overloaded. (The bulbs rated at 50w may actually be drawing everso slightly more too)

Have you tried disconnecting just one of the lamps in both circuits?

This will put less load on the transformer (obviously!)

If this solves the problem, I would buy another transformer (150w) and connect only two lights to each one.

I personally never like taking things to their max and always oversize a little!

Sparks...

[Bill Gardener]

Good idea thanks!

If this is the problem could I just replace the transformer with the

[Bill Gardener]

Good idea thanks!

If this is the problem could I just replace the transformer with the 210W model:

[Harry Bloomfield]

On 30/12/2003 Bill Gardener opined:-

You are using the word 'flicker', do you mean an absolutely steady and consistant flicker, or one where the level of light varies randomly?

The first would suggest it is a flicker at the mains frequency of 50Hz and the second still due to a poor connection. You would be able to notice the effect in a normal 240v lamp. You have ruled out a problem in the lighting circuit, by connecting to a 13amp socket.

A 50Hz flicker is not normally seen in tungston lamps due to the thermal lag, but you can often see this flicker in a TV picture or a florescent light. Are you running these LV lights close to a lit florescent light perhaps?

I can't really think of any affect which might be a result of the tranformers being overloaded, other than the transformers over heating and the lights being slightly dim, certainly not a visible flicker. I have a 250va transformer feeding 5x 50w lamps in my summer house with no eveidence of flicker and it is usually recommended that the transformer is a good match to the load.

My only suggestion at this distance, assuming we are talking of a 50Hz flicker, is that your eyes may be ultra sensitive to the flicker and to invite someone else to give a second opinion.

Sorry, I am really scraping the bottom of the barrel for ideas....

[Harry Bloomfield]

Harry Bloomfield wrote on Tuesday (30/12/2003) :

Just another long shot.....

I don't suppose you have the transformers wired via a dimmer switch have you? The transformers will not appreciate being wired via a dimmer and this can cause flicker.

[Sparks]

Yes, but it would be cheaper to simply buy another single 150w one and use the original ones!

You can run the lot of one transformer (as long as they are not miles apart!)

The total load from the lamps would be 50x6=300w - I would use a 350-400w transformer for this.

But as I said before, it would be cheaper to buy another 150w one and just wire two lamps per transformer, making use of the existing ones!

Either this, or change the bulbs for a lower wattage!

Sparks...

[Bill Gardener]

The flicker is hard to describe, both my wife and I have noticed it. It is not random but is very fast (50Hz maybe). I have even tried flipping all MCBs at the consumer unit so only the lighting circuit is on and also turning off all other lights in the house. The flicker is still there. Sorry it is hard to describe.

I have wired the lamps in parallel via a junction box to each transformer. Would wiring them in series help?

No dimmer switch just a normal wall switch.

Also why would the flicker appear after 10 minutes of use?

Bill

[Sparks]

Nope, you will get very dim lights then, since the voltage will then be shared, not the aperage

To me, it looks as if they are overheating, cutting out for a very short period, then turning back on, only to repeat hence the flicker!

How fast are we talking here, something that is barely noticeable, or a blatant flicker?

Can you count the "flickers" in a 5 second period, or is it way too fast?

Sparks...

[Bill Gardener]

Way too fast, the lamps are just not steady.

[Sparks]

OK, I would try the removing a single light in each circuit, then tell us what that did!

The fact there is a time delay of about 10 minutes before it does it tells me it is an overheating problem.

Where are the transformers located? - do they have space to breathe?

Sparks...

[Bill Gardener]

Yes trying this tomorrow morning.

In the space between kitchen ceiling and upstairs landing. Plently of space between joists. Lights flickered when floorboards were up so not a ventilation problem.

Bill

[mike ring]

"Bill Gardener" wrote in news:3ff1e918$0$13343$ [e-mail]:

Oh, come ON, I can't wait till then!

mike r

[Harry Bloomfield]

On 30/12/2003 Bill Gardener opined:-

One further point, are we discussing an actual transformer, either ferro or torroid cored? These will be quite heavy, about the weight of a house brick. The other possibility is a switch mode type, which ought to work at a much higher frequency than the 50Hz mains frequency. If a badly designed SMPSU, then it might give rise to the effect you are reporting. An SMPSU would be relatively light in weight.

It depends what you call series. With the 3 lamps in series they would each receive about 4v each (12v/3 = 4v) and would be very dim, so no.

[Harry Bloomfield]

mike ring wrote on Tuesday (30/12/2003) :

My money is on unstable SMPSU's oscillating :-)

[Harry Bloomfield]

On 30/12/2003 Harry Bloomfield opined:-

I've never heard of an overloaded/overheated ferro transformer on a resistive load oscillating like this.

[Dave Liquorice]

The image in the link previously posted looks like an electronic transformer aka a SMPS. Add in the 10 min delay then I suspect they are overheating and shutting down/becoming unstable.

Check the specification of the transformer, is it capable of driving 3 x 50W lamps. Yes, they maths is OK but practice is another matter...

It would also be fairly important that each transformer only feeds 3 lamps. The two transformer outputs are best completely isolated from each other.

[Dave Liquorice]

Probably not a problem with electronic transformers but under loading a real transformer can shorten bulb life as the voltage has not been "pulled down" enough by the load.

Agreed, but the amount of "oversize a little" is variable.

[Chris Oates]

no - the result tends to be a worrying smell.

While we're on halogens - what do people pay for 12V 50W jobbies ? - I was stunned to see them in Woolies for IIRC £4.99 each !!

I pay 58p

[Sparks]

58p! How many do you have to buy at a time to get them that cheap!

(I presume we are talking about the little dichoric ones that look like this

) If so, are the 58p ones open or closed!

...and where do you get them!

Sparks...