inductive field question

[WildRice]

OK, I have a project going on. Basics. a disk roughly the size of a CD, spinning with a motor on the center. I need power on the disk. I tried mechinical ie. brush. this didn't work, and I can't use batteries. I tried some tests with high strength magnets and coils on the disk. that didnt work.

My question is... if I wrapped a coil around the outside of the disk (approx 5" dia) and made a similar coil stationary, and in close proximity to the spinning one, and ran 5-10Khz in the primary coil, will the spinning coil be able to pick up the induced current.

I thought I would ask here before I try this out.

Thanks in advance

Jeff

 

[drs2000]

Should work fine. Even 60 Hz should work. You'd just have an air-core transformer, with one coil spinning.

The higher freq would couple better..

Sounds like fun. Good luck! DRS the crazed..

 

[Doug Owen]

How much power are we talking here anyway?

For sure both brushes and moving coils work, at least there's a pile of auto alternators depending on those two technologies every day....

What you suggest should also work, but it 'really needs some iron' to help define the magnetic fields. I would guess the best results would be at fairly low frequency.

However either the other two (brush or 'alternator') have more going for them, each is often used for this purpose.

Can you give some more of the details?

Doug Owen

 

[Steelwolf]

This sounds almost like the hand-cranked generator I own. Difference is the coil is stationary (output goes to bulb), while the magnets spin. I would suggest that if the required power on the disk is small, you could use a couple of permanent magnets stationary behind the disk.

On the disk side facing the magnets, you could have several coils of enamel-coated copper wire, wrapped so that the strands run perpendicular to the direction of travel. You will probably have to balance the weight with another set of coils on the opposite side. They could be either air or ferrite core. The ferrite core will give better results. (PM me if you can't visualise what I'm getting at.)

IIRC, stronger magnetic field gives more power, faster spin speed gives higher voltage, more coils give greater current. The output from the coil is AC so you may need a rectifier.

Realise that the electrical power in the coils is converted from the spinning mechanical motion. So the disk will slow down according to how much electrical power you are trying to convert.

Just re-read your post. I am quite surprised that you couldn't make brushes work, nor did magnets and coils give you satisfaction. How much power do you need? How fast is the disk spinning? Can you sketch and show us the things that you have tried before? Lots of DC and AC motors use brushes. Lots of generators use magnets and coils. Perhaps you did not set it up properly?

 

[WildRice]

OK.OK. Here are some details. I removed the light circuitry from a play fan, you know, the one with the 5 leds in the middle that make light patterns as it spins. I used 5 3mm leds (G-B-R-B-G) and 470 ohm resistors to decrease brightness and lower current. These are mounted and a lid from some electrical tape. I am using a small flat motor to spin this 'disk'. Final home will be in a frame for desk or wall, when the balance is correct. I tried using the shaft from the motor and a brush just off center for power. it made a TERRIBLE scraping noise and added some drag. I just tried a coil wrapped around the outside of the 'disk' not really efficient. BUT, I did find some coils from a small stepper motor, about 1/2" dia. I am testing mounting this on the drive motor around the shaft (the shaft is adding some core material) and the other matching coil will sit on the opposite side of the plastic lid at the end of the motor shaft. No idea on current draw, pretty small though. when I tried stationary magnets and coils on the lid, even with a shot diode and cap configuration, the duty cycle was too low to maintain brightness durring travel.
I'll leave some updates and pics when I get it working well.

Jeff

 

[WildRice]

Re: inductive field question (pics)

OK. got the rough part working and pretty well balanced.
I ended up using 2 matched coils from a small stepper motor.

Here is the unsuccessful try with a coil wrapped around the outside

Here is the motor with one of the coils attached.

assembled

And running.

Now just to breadboard it and find a frame.

Jeff

BTW peek freq=79.3Khz

 

[AilSnail]

Re: inductive field question (pics)

why do they blink at different frequencies and duty cycles?

 

[WildRice]

Re: inductive field question (pics)

the 5 led driver board is from a toy that when spun would make different light patterns. you can see the board in the pic that is not spinning.
Jeff

 

[LiteFreek]

Re: inductive field question (pics)

Looks pretty cool. Reminds me of a similar toy. It was a small clear plastic dome on a black plastic base. There were control knobs on the base that would adjust the speed and pattern of leds that were spinning around in the dome. Very fascinating. Wish I could find one of those again for my "toy" collection.

 

[WildRice]

Re: inductive field question (pics)

kinda like this.


web page

Jeff

 

[LiteFreek]

Re: inductive field question (pics)

Yah, that's it! Cool it's even in my state. hehe I might hafta check that out. Tis a neato led toy.