Any Sparky's - And I mean Electricians! ;-)

Hi all,

just wondering if there are any electricians amongst us who could help me with a small electrical dilemma?

I have some low voltage garden lights that I've had in the garden for years and they work wonderfully. The problem is that the missus has re-landscaped the garden meaning I now have to add two more lights. Not a problem as I have the lights. There are 4 lights, all of which are 12v 7w running off a 32w transformer. Now here's the question, if I added two more 12v 7w to the line what would happen? Would the transformer blow up, all the lights would run dim, or it just wouldn't work? I could get away with adding only one extra light as I have two separate chains. Or is it a case of trying to source a higher rated transformer. Of course I could just get 12v 5w bulbs instead. Which is the best option?

Any help would be greatly appreciated! Thanks in advance

Well, overloading will cause extra heating of the transformer.
If it's well designed, it will have a thermal cutout and possibly an overload circuit as well - it will then shut down to protect itself.

If it's a nasty cheap one it may work...and then overheat, short a few turns and blow a fuse. If it's a really nasty cheap one from China it might just burst into flames instead.

At the very best, it'll run hot, and have a drastically reduced life. When I designed power systems for aircraft we worked on a design rule that a 15C rise in temperature halved insulation life.

Your two suggestions are good - lower power lights or a bigger transformer. Personally I'd go with lower power lamps.

yeah, as above...

I reckon from what I see of faulty transformers, you will melt the transformer, which will then stop working or cause a fire.... but if you put that load on I reckon it would too hot to hold after 30 minutes (and I reckon the transformer will be cheap and therefore will have no protection on it)

I agree, to derate the lamps is a lot cheaper and easier than sourcing the transformer then fitting it....

but as a sparky... I just gave my wife a headtorch electrical aparthy sets in when I get home

John

Go on John...tell 'em your surname...go on go on go on

Circuit

Brilliant.

I always wanted to be a florist... but noone would take me seriously :cry:



John

There is a electrical goods place near you (well compared to me one in Cardiff the other in Swansea) called TLC
http://www.tlc-direct.co.uk/ I've used the online store before and they where fine and dandy.

other online electronics stores (Farnell/Rapid) should have LV PSU's as well.
Think I got my last one from Farnell.

Thank you very much one and all

I'll go down the route of lower wattage bulbs, the wife would never forgive me if I burnt the house down

Thanks once again