Air-core transformer design for propeller clock

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panalog9

Joined: 25 Feb 2002
Posts: 339

19 Nov 2003 23:32 propeller clock design

Hi -

Short question is, what is the best way to get power to a rotating part, like on a propeller clock ?

A good method seems to be to use an air-core transformer. The primary is stationary, and transfers power to the secondary which is mounted on the rotating part.

See these links for some samples :

http://web.wanadoo.be/henkenkatrien/propellerclock/
http://hot-streamer.com/hilo90mhz/electronics/prop_clock.htm

But what is the best/most efficient way to do this ? There are two basic methods :

1) Transformer. Coils are wound in phase, and power is sent over to secondary while primary is conducting. Two diodes and capacitor or two serve to smooth the power. Input waveform should be a nice clean sinewave.

2) Flyback transformer. Coils are wound out of phase, and power is only transferred when the primary STOPS conducting. The collapsing magnetic field generates the current in the secondary. Again, diode(s) and caps to smooth the power. Input waveform should be a ramp, rising smoothly, then shutting off sharply.

This is the theory at least - is this correct ? I've played around with it a bit, but not with much luck. I can't seem to get enough efficiency - not enough power to get to the rotating secondary.

-pana

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Aoxomox

Joined: 18 Jul 2001
Posts: 90

20 Nov 2003 11:18 propeller clock transformer

Have seen this in an Instituite:

Within a gear they implemented a transformer with a rotating and a fixed half of a transformer to supply some 10kW. Additionally they made two rings on the surface of each transformer to send digtial control pulses from the fixed to the rotating side without beeing interfered by the magnetic field.
And last but not least they put a ring with a lot of LED's as a optical transmitter on one side and one photo diode on the other side.

This is how they implemented 3 different, almost interference free, energy / information channels.

I think your problem is the size of the air gap. If your mechanical construction is very precise you can reduce the air gap to a minimum and then use a forward converter.
If your airgap is much higher this technique will stress all your primary components and you will not be able to transfer a lot of power. in this case only a Flyback-converter makes sense.

hope it helps.
aOxOmOx