I'm trying to make a transformer - Page 1
Forum section: electronics / beginners

author: Tybe
author_rank: Contributor
timestamp: August 26, 2012, 11:44:07 pm
content: Hi!I was just wondering if anyone of You have knowledge in building transformers.I 'm trying to build one, but I think I have failed. I have only made the primary coil. I found a calculator that said i should have 128 turns of 3mm wire as primary. But it is shorting my 16A automatic fuse instantly.This one are pretty much standard steel, not the thin plates. So There will be much "eddy currents" i guess. Is this what blowing the fuse or does it not simply work with steel. The core are 80 x 100 mm. But It should have been 80 x 120mm due to the plans I got from a transformer calculator. (I just found out I misread. doh..) Thas a big problem also I guess. About that, Does anyone have a transformer calculator for Win7? Thanks

author: amspire
author_rank: Super Contributor
timestamp: August 27, 2012, 12:25:50 am
content: You cannot make a useful transformer out of solid steel. The eddy currents will be a killer. Any energy you are putting in the primary is basically just heating the steel, and that is about it. The higher the frequency the transformer need to operate at, the thinner the leaves of steel have to be, so with a solid steel core, you may be limited to a maximum frequency well below 1 Hz.Look at the piece of steel going through the center of the primary. If you draw a line around the circumference, you have an unbroken conductor - a shorted turn. If a transformer has a shorted turn, the inductance drops down to near zero, and it is no longer a useable transformer.Also you need steel with the right magnetic properties. The gaps you have in the joins will very greatly reduce the transformer performance, as well as radiating EMF big time. A single gap of 0.1mm will noticeably reduce the inductance of a steel core transformer which is why leaves are interleaved in a normal transformer.Is that steel across the middle of the transformer below the primary? If it is, it will stop most of the flux from the primary reaching the secondary winding.Your best bet may be to find a suitable sized mains transformer which is bolted together rather then welded, pull it apart, and then using that hardware to build your own design.Richard.

author: Tybe
author_rank: Contributor
timestamp: August 27, 2012, 02:13:12 am
content: Quote from: amspire on August 27, 2012, 12:25:50 amYes Its steel. I better find some use for this piece of steel for some other things then:) Thanks for the good info Richard! I can always roll up the copper wire back at the spool again. I just have to find a good substance for this project then. I dont think its easy to find some >5000W transformers to salvage though.. Any suggestions?And still I need a calculator software for win7 (turns and wire diameter). I dont think I can learn how to calculate myself.

author: IanB
author_rank: Super Contributor
timestamp: August 27, 2012, 02:24:02 am
content: It's much harder to wind a working transformer than your simple experiment.See here for a very good introduction to how to do it:http://ludens.cl/Electron/trafos/trafos.html

author: T4P
author_rank: Super Contributor
timestamp: August 27, 2012, 03:49:15 am
content: Hard to finddumpster dives can be possibleUnless you are photonicinduction

author: amspire
author_rank: Super Contributor
timestamp: August 27, 2012, 04:20:28 am
content: Quote from: Tybe on August 27, 2012, 02:13:12 amYou can do what many others do. Get old Microwave Oven transformers, cut off the secondary windings with the laminations in place, and add a new secondary winding. The transformers in a large microwave are probably about 1KW rating, but you could have 5 of them in series to make up a 5KW transformer. Typically the secondary needs about 1 turn per volt.The original secondary windings are very dangerous (several kV AC - scary stuff) , so don't bother powering up the transformer with the original secondary, unless you have to.

author: GeoffS
author_rank: Unknown
timestamp: August 27, 2012, 04:23:52 am
content: Quote from: T4P on August 27, 2012, 03:49:15 amHow does this comment have any relevance to the subject under discussion or are you just trying to boost your post count?

author: Tybe
author_rank: Contributor
timestamp: August 27, 2012, 04:38:47 am
content: Thanks alot as always IanB! Great link:)And amspire:) I have 2 micro wave transformers, and cut out the secondary windings. That is really nice for making low volt, high current by replace the thin secondary with a thick wire (3 Turns). The problem is that it is welded so it's impossible to put it apart and rewire it with many turns for getting the voltage I wish.

author: amspire
author_rank: Super Contributor
timestamp: August 27, 2012, 04:58:56 am
content: What voltage do you want from the secondary?

author: T4P
author_rank: Super Contributor
timestamp: August 27, 2012, 09:22:58 am
content: Quote from: GeoffS on August 27, 2012, 04:23:52 amQuote from: Tybe on August 27, 2012, 02:13:12 amSee my point? Why would i want to boost my post count anyway.

author: T4P
author_rank: Super Contributor
timestamp: August 27, 2012, 09:24:11 am
content: One problem with MOT's that they are intended for a short duty cycle maybe around 30-50%So push "rated" wattage and they will blow up