How to connect a toroid ? - Page 1
Forum section: electronics / beginners

author: Hextejas
author_rank: Frequent Contributor
timestamp: December 10, 2018, 11:38:58 pm
content: I have a toroid that i think might be acting up so I wanted to check the primary connection. It connects to a 115v AC wall outlet in the US.It has 4 wires on the primary side so they need to be combined in order to connect to the 2 wires of the 115v AC.The wires are blue, violet, grey, and brown.Presently the blue and violet are connected as are the grey and brown.Is this correct ?

author: Circlotron
author_rank: Super Contributor
timestamp: December 10, 2018, 11:57:12 pm
content: Sounds like your toroid has two primary windings that should be connected in parallel for 115V and series for 230V. If you have already connected the toroid to AC power like it is now and nothing unusual happened then all is well. If one of the primary windings was reversed then your toroid will rapidly begin smoking!

author: cdev
author_rank: Super Contributor
timestamp: December 11, 2018, 12:31:10 am
content: you can use a low ac voltage from some other transformer (test it first) for testing but keep in mind that even a low voltage can get stepped up quite a bit if its connected as primary to what is usually a low voltage secondary of another transformer that has a 120 or 240 v primary thats unconnected. 1 volts would likely be relatively safe under almost any common step up or step down condition, although I would still use a voltmeter's probes, not my hands, to test the windings. So you could use a voltage divider or something like that to give you a 1 volt transformer testing voltage that you can apply to any set of windings that gives you continuity to see what emerges from the others. Then mark down the ratio of whatever voltages you get to the testing voltage. That and its size should give you a good ballpark idea of what the transformer is meant to do.

author: ArthurDent
author_rank: Super Contributor
timestamp: December 11, 2018, 12:43:30 am
content: No guarantee but if the color coding is standard the diagram below might help. It would be a good idea to wire a 40 watt Incandescent bulb in series with the primary when you first power it up to see if your guess is correct. Bright light is bad, no light is good.

author: Hextejas
author_rank: Frequent Contributor
timestamp: December 11, 2018, 12:02:29 pm
content: Quote from: ArthurDent on December 11, 2018, 12:43:30 amThank you Arthur for the chart which leads me to ask:Blu/violet--->soldered togetherGrey/brown--->soldered together

author: StillTrying
author_rank: Super Contributor
timestamp: December 11, 2018, 12:40:43 pm
content: Quote from: Hextejas on December 10, 2018, 11:38:58 pmYou don't say what they're connected to.

author: Hextejas
author_rank: Frequent Contributor
timestamp: December 11, 2018, 12:51:25 pm
content: Quote from: StillTrying on December 11, 2018, 12:40:43 pmActually I did. The 4 wires on the primary side need to connect to the 2 wires, 115v AC mains coming from the wall. So, 4 needs to be combined into 2.

author: ArthurDent
author_rank: Super Contributor
timestamp: December 11, 2018, 01:26:21 pm
content: The right side of the chart I posted shows how they are combined and where they are connected. Still use the light bulb to test it.

author: StillTrying
author_rank: Super Contributor
timestamp: December 11, 2018, 01:28:30 pm
content: Itsoundslike the primaries are correctly wired in parallel for 115VAC as in AD's right hand diagram.If it has been previously powered up like that the phases of the primaries must be correct otherwise it would have instantly blew up!https://www.eevblog.com/forum/beginners/ask-determining-transformers-windings-phase/

author: Hextejas
author_rank: Frequent Contributor
timestamp: December 11, 2018, 02:32:39 pm
content: I think that it is faulty in that I have it wired correctly according to the chart and I get about 2v AC as output. I contacted the vendor and I can return it. Somehow the beast went bad, but no smoke, lights, etc.Thanks all for the help.

author: StillTrying
author_rank: Super Contributor
timestamp: December 11, 2018, 03:16:10 pm
content: If that's with no load, "2v AC as output"soundslike leakage across an open circuit secondary.With it all disconnected, you could measure the DC resistances of all the windings to prove it.

author: Hextejas
author_rank: Frequent Contributor
timestamp: December 12, 2018, 11:05:21 am
content: Quote from: StillTrying on December 11, 2018, 03:16:10 pmFor my education I am trying to reason out how I would measure this. Additionally I didn't know about DC resistance. Are there AC resistances ?And to measure the resistance where would the probes be placed ? Between leads on the secondary ? Also between leads on the primary ? I am visualizing the picture of a transformer.

author: Zero999
author_rank: Super Contributor
timestamp: December 12, 2018, 11:30:55 am
content: It's possible one of the primary windings has gone open circuit. If you connected it to the mains as you described in your first post, which is opposite to schematic posted by ArthurDent, I suspect it's blown. The fact there was no smoke doesn't surprise me as the thermal fuses would have tripped to protect against fire.Measure the DC resistance of all of the windings with a multimeter. The primary windings should be similar and the secondary much lower. It's difficult to estimate the rough expected values, without knowing the power rating of the transformer. I suspect this is a fairly small transformer? Had it been over several hundred VA, then the circuit breaker in the house would have tripped.

author: Hextejas
author_rank: Frequent Contributor
timestamp: December 12, 2018, 11:58:32 am
content: This is it and it's quite heavy..500va prolly overkill

author: Hextejas
author_rank: Frequent Contributor
timestamp: December 12, 2018, 12:09:01 pm
content: Quote from: Hero999 on December 12, 2018, 11:30:55 amI really owe y'all an apology. I misstated in my original post. Since then, I have returned the toroid so I can't double check it but I think that I had it correct according to Arthur's chart.Sheesh!

author: StillTrying
author_rank: Super Contributor
timestamp: December 12, 2018, 01:01:45 pm
content: Quote from: Hextejas on December 12, 2018, 11:05:21 amAC resistances are usually called impedance, to give a clue that there's AC involved.For a 100% pure resistance, theDC resistanceandAC impedancewould be exactly the same ohms value.In practice there's no 100% pure resistance, there's always some inductance and capacitance even it if doesn't appear until the AC is a very high frequency. You'll have to do some googeling!http://www4.hcmut.edu.vn/~huynhqlinh/olympicvl/tailieu/physlink_askexpert/ae517.cfm.htmQuote from: Hero999 on December 12, 2018, 11:30:55 amIt should still be working if only one primary had gone OC. I imagine you'd have to be quite unlucky to OC both primaries on 115VAC.

author: Zero999
author_rank: Super Contributor
timestamp: December 12, 2018, 04:03:05 pm
content: Quote from: StillTrying on December 12, 2018, 01:01:45 pmYou're right of course. It should still work if one of the primaries had gone open circuit, if they were connected in parallel and it's highly unlikely they would both go open circuit.Quote from: Hextejas on December 12, 2018, 12:09:01 pmThe dots indicate the transformer's phasing and should both be connected together.I did a bit of Googling and found the technical brochure, which contains links to a clear data sheet.https://4donline.ihs.com/images/VipMasterCap/Capacitor/AVEL/AVELS00030/AVELS00030-1.pdfI think it would have blown the breaker, if you got the phasing wrong. It doesn't give the primary series resistance, but it does specify the copper losses and the resistance of the primary can be estimated from that. Here are the calculations:The efficiency is 95.1% and the transformer is rated to 500VA.PIN= 500W/0.951 = 526WI = P/V = 526/120 = 4.38AThe copper losses are specified as 23W, assuming half of the power is lost in the primary and half in the secondary:PLOSS(PRIMARY)= 23/2 = 11.5WSo we have a primary current of 4.38A and power dissipation in the primary's resistance of 11.5W, so we can calculate the resistance, using Ohm's law:R = P/I2= 11.5/4.382= 0.6ΩOf course half the current flows through each of the primary windings which are connected in parallel, so the resistance of each winding will be double that, but they're connected in parallel, so that's the resistance they'll present to the mains, if connected out of phase.I = 120/0.6 = 200A.200A will cause the main circuit breaker to pop very quickly.

author: Hextejas
author_rank: Frequent Contributor
timestamp: December 13, 2018, 12:49:25 pm
content: Hero99, you did quite a bit of work on this and I thank you.