Hi, since it is my first post i'll first introduce myself. I recently became interested in electronics as a hobby. I studied economics and work as an accountant in the sunny Spain. Since this is a hobby for me i am taking it with calm and slowly reading and watching videos to understand the basics.
So please be nice with me if i ask stupid questions at first.
As many people recomended i wanted to build a power supply for my "lab"
I have a couple of old laptop chargers and at least two old computer powers supplys but i wanted my first bench power supply to be linear.
Where i live temperature can easily get to 40C in the summer so i have to be very carefull with heat.
My supply is going to be (at first) powered by the venerable LM317 so that means 1.5A at most and not more than 15W of power being dissipated as heat. I will eventually move to a better design with pass transistors but i want to keep it simple at first.
So, asuming LM317 as my regulator i was going to use a 7.5-0-7.5 center tapped transformer (at least 2.6 amps per tap). If my understanding is correct i could use one of the taps as ground and use a relay to switch between the center and the other tap to get:
7.5v AC x 1.414 - 1,4 (rectifier bridge) = 9.2v DC which i can regulate between 1.25 and around 6.9v and
15 x 1.414 - 1,4 = 19.8v DC which i can regulate between 7 and 16.8 v
So far so good but i have a few doubts where i could use your help.
My first question is, how do i switch between taps, will a simple switch connected to a relay be enough?
Second, i've seen videos of people showing how to make your own transformers. Being able to make a custom transformer will allow me to add more taps to work more comfortably at bigger voltage ranges. Does it make sense? Is it something that a beginner can do?
Another option is using say two 6-0-6 transformers (primaries in parallel, secondaries in series) to get a 1.25 to 30v supply. Would it work?
Can I add extra taps to an off-the shelf toroidal transformers (assuming the primary is not being fully used)? For instance i could buy a 5 or 6 amps toroidal and add extra 5v and 12v taps for the voltmeter and fan, respectively? Will it add more ripple to my supply?