Transformer size

[deuce22]

Hi.

Can someone please let me know what size transformer I need for low voltage downlights.

There are 7 20w bulbs.

Thanks.

 

[bernardgreen]

Assuming you mean an electronic "transformer" and not a wound transformer.

7 times 20 watts is 140 watts.

So the transformer's continuously rated output power has to be greater by at least 10% ( 50% if halogen lamps ) than 140 watts and its minimum load rating must be less than 140 watts.

Dimmable or non dimmable ?

The output voltage must match that of the lamps.

 

[ricicle]

You don't need a transformer for low voltage downlights - you need one for extra - low voltage ones though.

7 x 20 = 140w. Transformers are rated in VA which is more or less the equivalent of W in this case so you are looking for around a 150VA transformer in this case unless manufacturers literature specifies a greater margin of spare capacity.

 

[deuce22]

Thanks guy's.

The choice was between a 150w/va and a 210w/va.

Is this something that an electrician should know. Although he hasn't been doing it long (about 18 months) he didn't know which one I would need and asked me to find out.

 

[timtheenchanter]

personally Id have more than one transformer, then if the transformer dies. you dont loose all your lighting.

 

[bernardgreen]

My choice would be a wound transformer that has no electronic components.

 

[flameport]

Is this something that an electrician should know.

Yes - it's very basic stuff.

Although he hasn't been doing it long (about 18 months) he didn't know which one I would need and asked me to find out.

So they have been doing electrical work for 18 months with apparently no understanding of the most basic concepts.

 

[RF Lighting]

He isn't an electrician, and he certainly shouldn't be designing jobs after only 18 months in the industry.

Multiplying the number of lamps by their wattage to work out a transformer size is THE most basic calculation. I seriously advise you to look for an actual electrician to carry out this work for you.

 

[deuce22]

He's someone that a plumber friend has been using and when he did first fix he had another electrician with him.

Now he's doing second fix, he is on his own.

 

[ban-all-sheds]

He's not an electrician.

 

[Lectrician]

If it is for standard downlights, I would be fitting a transformer per fitting, for the price these days you can't really argue!

This avoids issues when the transformer fails (loosing all lights) and also means if someone swaps a 20watt for a 50watt with out consideration, it will not cause issues.

 

[sparkybird]

and he's got a cheek - asking the customer to find out the info - can't he do that himself? He might learn something for next time then!