Can i use 2x12v transformer as one secondary with 24v output?

[JebemMajke]

Two secondaries, each one with 12v. I;ve read somewhere that if i connect V1 and V2 with each other and 01 with 02 I'll get 24v. Well actually guys were implying that I'll get around 35v. If that is true could I use lm317 as a regulator to put it down to 24v? With some capacitor filtering of course.

[Seljer]

Yep. Just wire the secondary windings in series. Just make sure to get the polarity right because you can make windins cancel each other out (quickly verified by hooking up yout multimeter in AC voltage mode).

You're going to get 34V after the turning it into DC because AC voltage is rated as root-mean-square value, so if add the diodes and capacitor you end up with peak value which is 1.414 times larger then the RMS. Read the great article on power supply at geofex

[PRR]

Connect one secondary to the other (NOT one secondary to itself!). Measure across the free ends. You either get 25V or zero V. If zero, use a different end on one secondary.

USE CLIP LEADS!! Don't hold 24V wires by hand! It's pretty unlikely to kill you, but on a hot sweaty day 24 Volts can give a real strong tingle which can make you jump, even slip and fall.

As Simon explains: 24V rounded AC sine wave has a Peak of 34V, and that's what the rectifier and main filter cap will get. In my experience you really get 37V DC at light load, sagging under 30V DC at heavy load. Note that many 3-pin regs are rated 35V max in-out, and at start-up their output is normally "shorted" by a heavy cap across the load (your circuit). So momentary 37V across a 35V part. They usually survive this. Yes, this is a good plan for regulated 24V DC. Be sure the '317 has enough load, either a 2K dummy load or low-enough resistors on the volt-set network. Unloaded '317 will soar above set voltage. Using 220 ohms for the op resistor is often enough. 120 ohms will cover worst-cases, but at 24V the bottom resistor must be larger than 1/4W.