down light transformer question

[GPack]

Hi there,
A quick question on 12V down lights and their repective transformer.
If I am using 1 transformer per downlight, is a 10-60VA transformer suitable. I have been told in the past that if the lamp goes the transformer will burn out and if so what is the best one to use? The lamp is a 50W halogen. Would quite like to nail this one and wipe away another myth maybe.

 

[Adam W]

You could use one with a minimum output of 0VA, then when the lamp fails it won't take the transformer with it.

 

[GPack]

So will the 10-60v fail?

 

[nickblake]

It is incorrect to advise you that the transformer will go when the lamp goes , not always , on occasions it may well take out the transformer , this is due to the resistance of the lamp filament basically shorting out the transformer , the majoritory of the times the lamps blow open circuit ,or fail due to the life of the lamp expiring ,the lamp lifegiven is also a estamated guide for the length of the life of a lamp not how long the lamp will last , as for the size of transformer i have found that the 60 va and 50 watt lamps although are correct, causes the transformer to run hot especially when surrounded by insulation , so i install 102 va transformers and have found doing makes them more reliable and less likely to fail ,

 

[GPack]

this is due to the resistance of the lamp filament basically shorting out the transformer ,

How does this work?

 

[nickblake]

basically what happens every time you use a filament light the filament heats up , over days weeks years (youll be lucky with 12volt 50 watters ) the resistance and elasticity of the filament decreases , this decreases to the extent that the resistance is so low that it causes a short , have you ever turned on a light and heard a tink and a bright flash and the MCB trips this is what happens on normal filament gls lamps

 

[GPack]

So if there is a short what is the actual affect on a 10-60VA transformer? Does this have the same affect on a 0-60VA transformer. Thanks for your help on this. It can be quite difficult getting straight answers when talking to people to try and learn a bit more.

 

[Adam W]

I don't know if this is strictly correct but the way I look at it if a lamp blows open circuit there will be a load of 0VA on the transformer, which could cause problems if the minimum load is 10VA.

 

[GPack]

I've just been reading quite a good site about this. The transformer we are using has an autoreset capability. If there is a Short Circuit or overload condition the transformer will stop working unit the condition has been removed, then auto reset and continue working. It maybe that, as you say, older transformers that were expecting a minium load of 10VA would have burnt out if there was no load.

LED Home Lighting | Replacing 12v Halogen Lamps | KuleKat . comhttp://www.kulekat.com/led-home-lighting/led-home-lighting-a-buyers-guide.html#LEDDriversAndDimmers

This link has some really useful advice about downlights, 230V/12V/ and LED lighting. Definitely worth a look if you don't know too much about it and are keen to learn more like me.

 

[Shocking]

A friend of mine has got a problem with down lighters not to sure if they are 12 v or 230 going to have a look saturday, one lamp blew now the other 5 downlighters on that switch dont work, would just changing the bulb that is blowen fix the problem or could it be a transformer problem now. the building the flats in is about 4-5 years old.

Any help guys

 

[Amp David]

Probably got the 5 lights on the same tranny and its gone pop.

 

[Shocking]

Thanks David that wat I was thinking! guess Ill have to pop some lights a feel around in the void, if thats the case should I put a Transformer on each light or just replace the single transformer?