Toroidal transformer design questions - Page 1
Forum section: electronics / beginners

author: made2hack
author_rank: Frequent Contributor
timestamp: March 25, 2017, 11:18:05 am
content: Hello all,I am building an isolation transformer using a toroidal transformer. I want to position the output electrical socket in the center of the toroid to save space, as in the attached picture.Question 1:Will this be a problem? Will the magnetic field affect the output voltage or vice versa, will the socket take away from the functioning of the toroid?Question 2:For the input, I am using an IEC socket with 3 wires, Live, Neutral and Ground. What do I do with the earth ground? Do I just leave it floating? The case I am using for the transformer is ABS plastic, and since it will be an isolation transformer, I am obviously not going to create a ground on the Secondary to connect to the Primary.Thanks,

author: Benta
author_rank: Super Contributor
timestamp: March 25, 2017, 11:23:28 am
content: Q1: NoQ2: leave open

author: HighVoltage
author_rank: Super Contributor
timestamp: March 25, 2017, 11:32:14 am
content: Benta is correct.This will be a nice design.Show us some pictures, when you are done with everything.

author: made2hack
author_rank: Frequent Contributor
timestamp: March 25, 2017, 12:02:47 pm
content: Thanks guys,Definitely will upload a video once it is complete.Regards,

author: Ian.M
author_rank: Super Contributor
timestamp: March 25, 2017, 02:18:34 pm
content: Avoid any metal mounting hardware forming a shorted turn. Also wiring to the socket should either all pass through the core or none of it.

author: MrAl
author_rank: Super Contributor
timestamp: March 25, 2017, 06:38:44 pm
content: Hi,In a toroid design any material that can conduct current and goes through the center constitutes a single turn. This means that if there are wires connected to the socket any they go through the core those wires will be affected, and any metal that makes up the contacts will be affected.How they are affected depends on how they are situated inside there. If one wire goes through the center series aiding it will add to the voltage, if one goes through series opposing it will decrease the voltage. If one goes one way and another goes another way they may cancel each other out.So as you can see, it's a little hard to predict without having a drawing of the exact construction and without knowing what the turns per volt ratio is. This means a simple test is on order. Simply allow the conencting wires a little more slack when the thing is first built. Try the device with the socket NOT in the center of the core, measuring the voltage and input current. Then push the connector into the center where you need it, then measure again. See if there is significant change. After it is pushed in, you also have to test for heating. The eddy currents in some metals will be much greater than in the toroid metal, so after running for several hours see if the socket feels hot or even starts to melt.My gut on this is that it wont matter, but tests can be done to be absolutely sure of this or prove otherwise.

author: made2hack
author_rank: Frequent Contributor
timestamp: April 03, 2017, 05:41:35 am
content: Should I add a layer of foil in between the two windings to prevent capacitive coupling?How would I wire that layer? On wiki, it says it is connected to GND. Is that primary GND?

author: made2hack
author_rank: Frequent Contributor
timestamp: April 03, 2017, 10:08:20 am
content: Ok got it thanks