Transformer magnetic flow - different windings - Page 1
Forum section: electronics / projects

author: rodrigopires
author_rank: Regular Contributor
timestamp: June 28, 2016, 10:12:37 pm
content: Hi everyone! I´m making some changes to my old MOT arc welder and i got some ideas, but before i start to change thing i want to know if theres any diference and or improvement. My current welder consists of two MOT's with primary in parallel and secondarys in series. It does its job, but i wanted to make more clean, i guess, and try to turn the two transformers into one. So i though in puting the two E cores facing each others in order to complete the trasformer. Basicly is just taking out the I parts and puting them together. My question is, what's better, whats is different and if it works at all. In the attachments are my designs, my current one with the two separated transformers, and one with the primary on each side (each tranformer part) and secondary on the middle, the other has the two primarys together and the secondary on top.Thanks!

author: johansen
author_rank: Super Contributor
timestamp: June 28, 2016, 10:39:57 pm
content: Make sure the two primary coils have exactly the same number of turns. anyhow, the first photo, PSP is better as there is less leakage inductance.However, you may want the leakage inductance to make the volts/amps curve of the transformer more reasonable for welding.

author: rodrigopires
author_rank: Regular Contributor
timestamp: June 28, 2016, 10:49:31 pm
content: Yes, the two transformers are the same, just as the two primarys are the same. And since the transformer will practically operate at short circuit, how is that leakage inductance afected in the two models?

author: johansen
author_rank: Super Contributor
timestamp: June 30, 2016, 12:26:58 am
content: In the third photo, PPS will have significantly higher leakage inductance than the second photo, PSP, which is what i intended to communicate to you in the first post.welders don't operate at short circuit, there is usually something like 15 to 40vac across the arc during operation.anyhow, try both configurations.

author: rodrigopires
author_rank: Regular Contributor
timestamp: July 06, 2016, 02:44:18 pm
content: So i tryed the PSP version and let me say it works amazing! I fitted all the wire i had and could still fit more. The secondary is at 53V which is ideal, my old configuration (two mot series) only gave me around 35v. I'm really happy with this tranformer! Using it with my homemade triac controller, i can choose the output voltage, from 23 up to 52V, It welds 10AWG (2,5mm) at 35V and 8AWG (3mm) at 47V, at 53V it gives a lot of power (big arks).

author: Circlotron
author_rank: Super Contributor
timestamp: July 07, 2016, 04:55:48 am
content: I didn't think it would work that well because you now have only half the core cross sectional area so presumably the VA capacity of the transformer(s) is halved.

author: JacobPilsen
author_rank: Regular Contributor
timestamp: July 07, 2016, 06:34:35 pm
content: Think not.He did't use haves of one core. He uses complete set of "E" cores, from two complete transformers.But lenght of average magnetic flux lines is now longer (about twice), it mean higher reluctance, and so on...

author: Circlotron
author_rank: Super Contributor
timestamp: July 08, 2016, 09:47:25 am
content: Think so.I wasn't talking about the total volume of iron, which is about the same as before but the total area of the centre leg(s). It has gone from two units of area down to one.

author: JacobPilsen
author_rank: Regular Contributor
timestamp: July 08, 2016, 10:29:28 am
content: I'm pretty sure that It didn't.The core cross sectional area in cm2(or in inch2) is exactly same.Quote from: rodrigopires on June 28, 2016, 10:12:37 pm