Transformers and 12v lights

[sherman0251]

I have already got installed 12v down lighters with 1 transformer per light. The transformers are 20-60VA.

I have just purchased 3W LED lamps (mr16) to replace the 20w 12v halogen lamps. When i put the LED lamps in the fitting they came on fine for about 5 mins then started to flash then went off and dont work anymore.

I have contacted the seller and he has said that it is because the transformer is too powerfull??? and it should have a minimum of 7 3W lamps connected to 1 transformer so that there is a minimum load of 20W on the transformer!
My understanding about transformers is that they only give out what is pulled from them up to their maximum rating.

Am I right or can some one explain???

 

[Chri5]

Unfortuantely there are 2 x types of electronic transformer. One's that work between 0- and a set wattage and ones that only work from 20w up.

Unfortunately you have the latter and will need to change the transformers, or rewire the lights to feed from 1 transformer of suitable wattage for the total of LED lamps connected.

See products at http://www.tlc-direct.co.uk/Main_In...lights_Index/Lighting_Transformers/index.html

 

[ericmark]

Your transformer is not just a transformer. It would be better called an inverter. The power going in is turned to DC and stored in a capacitance then it is turned into ac at a very high frequency because it is so high the transformer can be very small. The output is sampled and the bit making the ac is adjusted to ensure the output voltage is kept very steady. This means the quartz halogen lamp runs at exactly the right temperature so active material is bounced of the envelope back onto the element but not too hot to burn out. This is why the 12v versions give off more light per watt and last longer than 230v versions.

It is cheaper to make 20w to 50W than 1W to 50W so that is what was done. Newer versions allow for use of other than quartz halogen and have a wider tolerance. And very old was plain transformer and work from 0 to rated output.

The 230v version does have the advantage they will work with cold cathode (florescent) versions as well as LED and tungsten and all my new lights are the GU10 type with cold cathode and at 11W a reasonable output. Much better than older LED types. The newer LED's are brighter but expensive.

So now you have three ways out.
1) Wire them all to one transformer (Not best as if LED's blow then same problem).
2) Renew transformer.
3) Change to 230vac type.

If latter be careful to select fitting to take the slightly longer cold cathode lamps.

 

[Steve]

The 230v version does have the advantage they will work with cold cathode (florescent) versions as well as LED and tungsten and all my new lights are the GU10 type with cold cathode and at 11W a reasonable output.

Eric, While cold cathode and fluorescent are similar technologies, I think it is wrong of you to be mixing their terms around like you do. They are different types of lamp. Cold cathode illuminates immediately and runs on higher voltage - an example is neon. Fluorescent usually has a delay on startup and runs at 230v.