I have a transformer which I got from a alarm system and wondered if I can use it in conjunction with my newly purchased bread board.I don't know how I would tell what the transformer is, I'm assuming the input is 230v (UK) but the output I'm not sure. The resistances of the windings are 0.7 ohms and 74 ohms. I'm assuming the output will be around 23V? Also, if I was to use this, which winding would the mains connect to, the lower resistance or higher resistance?
If it is a mains transformer, then the primary and secondary windings will be on separate bobbin sections with an insulator between them. The higher resistance winding will be the primary (mains) winding, as it has more turns than the secondary and is made of thinner wire. (Resistance tests on a transformer are not generally very informative as most meters measure only the DC resistance, and transformers behave quite differently when supplied with AC.) The easiest way to find out what comes out of the secondary winding, is to apply power to the primary. That will give you the off-load voltage. To find out how much current you can safely draw, you will need to measure the temperature of the transformer under load. It's safe if it isn't too hot to touch the laminations (at the furthest point away from the mains terminals, obviously) with your bare hands.
