Get yourself a good 12v lighting transformer to supply low voltage power to your patio lighting, and all is well. But what is a good 12v transformer? And how do you know that you haven’t found an unsuitable type? Allow me to sort this question out for you.
The right type of 12v transformer simply converts mains voltage to 12v – AC or DC. You will know which type you need exactly, by looking at your light bulbs. It should be a rather simple task to find and buy the right type – and it is. Especially, if you shop at the right places, where the goods are clearly labeled and the information is plentiful. But what if you are either in the mood for a little experimentation, out to save some cash – or both? You might come to the conclusion that you have a little junk-box jewel somewhere, that might do the job for no money at all! Wouldn’t that be great? And sure – you may in fact have the right type lying around, ready to be put into action as a lighting transformer and it may even be clearly labeled with mains input terminals and 12v output terminals. Piece of cake, right? But get this: Even if it all seems to check out, even if it does put out 12 volts, if it has all the power your need, is fused, etc – it may still be bad news.
I’ll get to the point now. If that transformer is either an auto-transformer or a bipolar transformer, you need to make a full stop! An auto-transformer is used in many applications, including automotive uses, but I would never use it for patio lights or other outside lights – or any d.i.y lighting project at all! Why not? Because, unlike regular transformers, in an auto-transformer, there is a direct electrical connection from the mains terminals to the output terminals. This means that you could get electrocuted, even if you touch the supposed low voltage terminals! Never, never, never use these for patio lighting – or anything else for that matter.
The other type you should avoid is the bipolar transformer. This one is not so dangerous to you – but it might harm your lights. A bipolar transformer outputs both a positive voltage and a negative voltage, which means that there are 3 output terminals or pins, instead of just 2 – as on a normal transformer. If those terminals are incorrectly labeled – or not at all – you could accidentally connect your lights to the positive AND the negative pins – instead of the positive and ground, as you should. In this case, you will get the voltage difference between negative and positive, which is twice the rated voltage – 24v instead of 12v. Your lights may be fine with this – and they might not. Don’t chance it.