Help! Why the flicker?

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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:
http://www.screwfix.com/app/sfd/cat/pro.jsp ;?id483&ts289
Each supplying three 50W lamps:
http://www.screwfix.com/app/sfd/cat/pro.jsp ;?id423&ts289
I 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.
2. The transformers are causing the flicker.
3. 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
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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...
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Good idea thanks!
If this is the problem could I just replace the transformer with the
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Good idea thanks!
If this is the problem could I just replace the transformer with the 210W model:
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too)
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 50x600w - 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...
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On Tue, 30 Dec 2003 19:37:10 -0000, Sparks wrote:

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.
--
Cheers snipped-for-privacy@howhill.com
Dave. pam is missing e-mail
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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....
--

Regards,
Harry (M1BYT) (Lap)
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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.
--

Regards,
Harry (M1BYT) (Lap)
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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
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Sorry
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...
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Way too fast, the lamps are just not steady.
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fast?
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...
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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
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Oh, come ON, I can't wait till then!
mike r
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mike ring wrote on Tuesday (30/12/2003) :

My money is on unstable SMPSU's oscillating :-)
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Harry (M1BYT) (Lap)
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On 30/12/2003 Harry Bloomfield opined:-

I've never heard of an overloaded/overheated ferro transformer on a resistive load oscillating like this.
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Harry (M1BYT) (Lap)
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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
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"Chris Oates" <none> wrote in message wrote in message

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 http://tinyurl.com/2tpl3 ) If so, are the 58p ones open or closed!
...and where do you get them!
Sparks...
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Yes the little ones - I always buy open faced as they're not used in bathrooms - the address is http://www.suzo.co.uk/home/default.asp usually buy 20 at a time. they may refuse to deal with you or not have any. nothing to lose by asking though
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Chris Oates wrote:

90p, but mine seem to have infinite life. Newey and Eyre

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