Timeline for Even vs Uneven Magnetic Field Cancellation in Toroidal Transformers
Current License: CC BY-SA 4.0
8 events
| when toggle format | what | by | license | comment | |
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| Nov 1, 2018 at 1:33 | comment | added | Samzun | Ok. So generally the reason there is less magnetic field is because there is less loss in Toroidal core? Is it a principle that even escaping magnetic field can be considered as losses? Can't they be natural expression of the electrons without necessarily be expressions of losses? And the windings are said to shield the Toroidal core too. So which contributes more to magnetic field suppression in toroidal.. is it because of less loss or due to the winding shielding? | |
| Oct 31, 2018 at 13:44 | comment | added | Dan Mills | You misunderstand, for ANY transformer, the bigger the core is in relation to the total flux level the lower the external field (assume all else is equal). A 500VA part is NOT inherently better or worse then a 300VA one, but a 300VA unit wound on a 500VA sized core (but only running at the same total flux as the 300VA) will be better. Equivalently get a 500VA 350V primary to 175V secondary and use it as a 240V primary to 120V secondary which will be good for 340VA in that service but will run with a much lower external field because the magnetising current will be lower. | |
| Oct 31, 2018 at 13:11 | comment | added | Samzun | Ok. As summary. For normal EI core... the bigger it is.. the larger is the flux and magnetic field... So you are saying that for Toroidal core, the larger it is, the lesser is the flux and magnetic field? I only need 300VA. Should I buy 500VA just to have lower field.. or did I misunderstand you? | |
| Oct 31, 2018 at 12:55 | comment | added | Dan Mills | @Samzun Talk to a custom transformer winding company and get them to build you something with an oversized core and a flux band, the better sort of vendor will take your target numbers and make sure the thing meets them. You need to deal with a vendor because such things as the use (or not) of grain oriented steel for the core matters, as does the core tape geometry and the annealing, and your vendor will know their materials choice. If you need more then the vendor can do in the transformer (should not be the case) then a heavy mild steel sheet forms a reasonably effective shield. | |
| Oct 31, 2018 at 11:29 | comment | added | Samzun | I need just 5 milligauss at 20 inches away. Is this possible? What brand of Toroidal Transformer are known to have lowest stray fields so I can check its design? I think the windings have to be even to have lowest stray fields, so perhaps the better quality brand, the better is the symmetry, right? Or are those cheap china brand and top brands same in the stray fields performance? | |
| Oct 31, 2018 at 11:07 | comment | added | Dan Mills | Nope, flux is primarily proportional to applied voltage and inversely proportional to frequency. There is a second order effect where as a transformer becomes more heavily loaded the flux actually falls slightly (Due to the resistive copper loss of the primary being in series with the supply, so lowering the effective input voltage as the load increases), but this is very much a second order effect. What does minimal mean to you? You have to have numbers before you can design. | |
| Oct 31, 2018 at 10:29 | comment | added | Samzun | Say you have a 750VA capacity toroidal transformer and you are only using 500VA. Won't this produce the same flux as using a 500VA version at near saturation? Won't both produce the same magnetic field say 16 inches away? Well. I'm just using it along with magnetic sensors so need to have minimal stray fields. | |
| Oct 31, 2018 at 9:07 | history | answered | Dan Mills | CC BY-SA 4.0 |