Voltage distribution in bifilar wound coil - Page 1
Forum section: electronics / beginners

author: Felix64
author_rank: Newbie
timestamp: May 05, 2022, 11:43:56 pm
content: Hi everyone.I already asked this question in the thread of my last question but nobody answered so that is why I'm trying it again here.How would the voltage distribution look like in a bifilar wound coil used in a switching circuit for example?So I assume with a normal solonoid coil it would be like this: If the coil has 100 windings and the voltage across it is 1000V then there is around 10V on each turn/ winding.Does the same still apply for bifiliar wound coils? Or is the voltage distribution in a bifilar coil different?Thank you.

author: planet12
author_rank: Regular Contributor
timestamp: May 06, 2022, 04:06:36 am
content: Quote from: Felix64 on May 05, 2022, 11:43:56 pmIf the windings are truly bifilar - ie. same number of turns, very closely coupled - the voltage distribution will be the same (or at least very very close - small differences may occur just due to differences in the winding positions, since they can't physically occupy the exact same space).The main reason for multifilar winding, eg. Litz wire, is to reduce the increase in effective resistance due to skin and proximity effects that become problematic as frequency increases.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 06, 2022, 05:34:56 am
content: "Bifilar" refers to how the wires are arranged in the winding, not necessarily how they're connected: shall we assume they are connected in parallel at each end?And, are you asking for the quasi-static condition (where normal transformer action applies), or at frequencies higher or lower than that as well? (At DC, the answer is of course just due to the wire resistance. At higher frequencies (on the order of the wire length as 1/2 wavelength, for the parallel case), transmission line effects become evident, as well as the winding path: number of turns per layer, number of layers, wire spacing and insulation thickness, etc..)Tim

author: Felix64
author_rank: Newbie
timestamp: May 06, 2022, 04:28:32 pm
content: Quote from: T3sl4co1l on May 06, 2022, 05:34:56 amNo I mean when the the coil is connected in series like in a tesla bifilar coil.But I just found that there is also a hairpin bifilar winding.I would also like to know if that would make a difference again please.And I'm not sure about whether it is a quasi-static condition or not.The frequency for my coil is variable so I assume that means it's not.Thanks.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 06, 2022, 06:29:35 pm
content: Can you be more specific?This?https://commons.wikimedia.org/wiki/File:TeslaBifilar.pngThey're simply in series, so the voltage divides evenly between the two windings and the voltage between wires is about half applied or 500V in your example.Tim

author: Felix64
author_rank: Newbie
timestamp: May 06, 2022, 09:02:36 pm
content: Yes I meant this kind of wiring.So I assume then that it doesn't matter if the bifilar coil's wires are connected together for a hairpin bifilar or tesla bifilar configuration since they are both basically just series connected and the same thing you said applies for both of them.Thanks.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 07, 2022, 03:01:14 am
content: For a hairpin winding, the inductance largely cancels out, and the spiral or coil can be unwound to see that you simply have a transmission line with one end shorted. Thus it will have inductance corresponding to inductivity of the line (for a twisted or parallel pair, about 100 ohms Zo, around 300nH/m), and voltage between wires distributes according to transmission line behavior. (So, for low frequencies, inductance or resistance dominates, and voltage is linear with position, maximum at the driven end, zero at the shorted end. At higher frequencies, resonant modes give standing waves, and voltage and current can be much, much higher.)Tim