How to provide power to a spinning circuit ?

Hi all...

I need to make a circuit that needs to spin on the shaft of a small dc brushless motor. I thought I could use a permanent magnet mounted on the base of the shaft of the motor (not moving) and some coils that will be spinning on the pcb. I don't know if this will work or provide enough power (need 5mA) to the spinning pcb . Any better ways ?

BTW I can't seem to find a dc brushless motor manufacturer. Can you suggest any ?

Thanks

Slip rings?

One simple approach is to use a small motor with the body attached to your PCB and the shaft fixed. Attach a pulley to the body of the motor and spin it with another motor. Take power from the leads of the motor attached to your PCB.

power

more than one

enough

suggest

So is yahoo. Everything I hit seems to be large dc motors.

Thanks

Ok, let me ask the question since you seem somewhat reluctant. Are you going to have assemblers build these in large quantities will you build a few in your garage or somewhere in between.

I seriously doubt anyone here is going to steal your design based on what you've told/not told us.

Ok, how much do you expect to spend per unit?

Rules out slip rings. I'd use an inductive coupling. Sony and others have used them to power the preamp and/or deliver erase current on the spinning helical head assembly for videotape

Then add "fractional horsepower" to your search term.

As a point of reference for you: Dremel makes a lamp for their tools, which takes off power using magnetic coupling: It consists of a permanent magnet (this goes on the shaft of the tool) and a coil assy that wraps around it, and the coil is connected to two LEDs. Probably around 60mA.

Use a rotating transformer.

One way might be to modify the motor so you can draw power from the rotor windings.

Best regards, Spehro Pefhany

A bright lamp, and a solar cell... ? :)

You are going to need a generator of some sort. At such low speeds, the simple magnet/coil is going to struggle, so you probably need higher frequency resonant coupling ( see electric toothbrush chargers ) - these use ferrite coils, with a frequency chosen for maximum power transfer, somewhere in 15Khz-150Khz regions.

-jg

Have a high intensity LED, fixed to the chassis, shine on a "solar cell" fixed to the rotating circuit board.

A small-light-powered-calculator I pulled apart used an LED as a shunt regulator so evidently they can deliver mA no probs.

Robin

A really tiny windmill, perhaps?

This could be a cutting edge project.

He left out more than a few details (I have seen his responses to the above some of which were just a bit vague).

1. How much space do you have to play with
2. How much current does your PCB circuit require, what voltage.
3. Can the topology of the space be described, or better still, drawn and placed on a website somewhere.
4. What sort of environment is this for
5. Is power the only contactless transfer you require
6. How big is the circuit on the PCB and can a slightly larger board be accommodated.

The OP also indicated that he was looking for the supplier of brushless DC motors. PML Flightlink would be one outfit that he could try.

power

Take a look at this:

I enjoy helping people, but not when the questions are posed in a "smash-and-grab" style. If I'm going to give away my time and knowledge, I'd at least like my intellectual curiosity pleased out of the deal.

I think most of the regulars here would agree.

Hi Rodo,

How about transmitting a little power on a license free band such as ISM (maybe 13.65MHz?), picking it up via small coils on the shaft and rectifying it there.

Of course you'd have to check the legal situation in the countries where this is going to be marketed.

Regards, Joerg

Try a search for "Propeller clocks" they much power a spinning led bar

There is a great web page on this very subject:

How To Ask Questions The Smart Way

We tried it - the shaft is prone to get most of the power and convert it to heat due to iron losses. The coupling link geometry has to be designed so that the magnetic field hits the secondary coil but not the shaft and surrounding metal parts.

The solution in our case was a ferrite transformer at 20 kHz. The power transferred was small, some hundreds of mW. It showed that the transformer air-gap variation due to mechanical tolerances of shaft mounting had a pronounced effect on the transfer efficiency.

Tauno Voipio tauno voipio (at) iki fi

We agree, but some posters do need a little help in framing their questions properly.

Ahhh!! you beat me to it Guy. Great page for advice but a bit long winded (could all have been said in much fewer paragraphs).