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Custom transformer calculation

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Eagle_85:
Hi. I have an application for a sort of rotating transformer. Where the core rotates and one coil rotates/winds with it while the other coil is stationary and sliding on the rotating core.

I know the basic primary/secondary windings = primary/secondary voltage. But for my application i just need a sort of isolation transformer with the same voltage on both the primary and secondary side. All other transformer calculations like calculating the minimum number of turns needed for a given frequency and power level is like dark magic to me.

As i understand it you can use less turns if you go up in frequency right? And for my application i obviously want as few turns as possible because i can only have one layer of turns. So what frequency and core material can i use to transfer for example 12 volt and 20 watts? with maximum 30 turns on the coils

I have tried to illustrate what i am after here:

The ting on top is a pulley. And the round core is not attachet to the square return path part of the core and will rotate freely. The top coil winds/unwindes with the round cores rotation while the bottom coil stays stationary and just slides on the rotating core. Maybe it is better to just rotate the bottom coil with the bobbin than to rotate the core, but that is not important for the question here.

T3sl4co1l:
Why does it need to rotate?

I can't imagine where such a thing would be used, but I guess it could make a 100%-flex (elastic) "sliding contact".  Not sure that enameled wire would be so good on abrasion (the wire will inevitably rub against itself as it un/winds, or against the former if it's made with a threaded form, which would be the better idea as that allows some separation of the turns in-place).  Copper certainly isn't setting any records on stiffness or strength, but it's not bad at least (assuming full-hard wire is used).  A steel cored wire maybe, or perhaps some alloys, would be the next best option in terms of strength without sacrificing too much conductivity (but, while phos bronze, brass and such are stronger than copper, they're much less conductive too).

The usual rotating transformer uses two pot cores, or similar shapes.  It's radially symmetrical therefore doesn't matter how they rotate with respect to each other.  Windings are fixed with respect to each side, no flex, sliding or abrasion to worry about.  Spacing needs to be kept fairly tight, nothing a few bearings can't provide.

Tim

Eagle_85:

--- Quote from: T3sl4co1l on August 18, 2020, 08:46:35 pm ---Why does it need to rotate?

--- End quote ---

Because the purpose is to transfer electrical power from a stationary object to a slider without direct electrical contact because i want the wires to be isolated.

So this transformer is on the slider part, and the "winding coil" will drive the slider back and forth. And yes there will be a threaded part on the core where the winding coil sits and there will be better isolation sheath on the coil wire than enameled wire for better abrasion resistance.

T3sl4co1l:
How much isolation is required?

Why not a traditional sliding contact, or flex cable?

Tim

Eagle_85:

--- Quote from: T3sl4co1l on August 18, 2020, 09:00:11 pm ---How much isolation is required?

Why not a traditional sliding contact, or flex cable?

Tim

--- End quote ---

Because this application will be in salt water so it needs isolation both to prevent corrosion to the wire and to not "leak" power trough the conductive salt water. And the wires needs to be tight at all times, i can not have a loose flex cable dangling from the slider as the slider path is really long.

But my question is about the electric specification here, not the mechanics. Like i said how can i transfer for example 12 volt, 20 watts with a max of 30 turns? What frequency and core material do i need for that?

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