Want brighter LED flash from stepper motor, better circuit?

[Grant]

Hi there,

I have a small stepper, two windings, no centre tap. Says 4.2 Ohm on
the nameplate. This stepper has an extra gear wheel to get a fairly
fast turn speed.

I wired up two bridges with eight 1N4148 signal diodes direct to a
white 14,000mcd LED. Can get a fairly bright flash out of the
LED.

I'm wondering if there's a better way to connect the windings?

I put a picture of the contraption on:

http://grrr.id.au/image/small-stepper-8-diode-bridge-to-LED.jpg

The circuit is simple, a diode from each of the four stepper lines
to LED anode, and another four diodes going from each line to the LED
cathode.

Wondering if some sort of series winding be better? This is just
something I can give to a friend's kid to he can make some light
and see the components. One may run the thing up one's leg or arm
to create some light too.

Dunno if I should put any over current protection in there as well,
trying to keep it simple.

I did have a capacitor in there but it reduced light output, seems
the spikier the voltage, the better the light output.

Maybe a Joule thief type circuit? Ideas please?

Thanks,
Grant.

 

[Grant]

Putting the windings in series should be a bit better, as then the
output from one winding would not be (directly) driving the other -
which is happening now.

I think they were isolated, working in parallel before with two bridge
rectifiers.

And yes, much brighter with half the diodes and series connection

I tried a joule thief circuit on it but it needed a cap to get some
brightness, tried a supercap as well, but that didn't absorb much
of the voltage, tended to slowly build up to say 1.5V then drive the
joule thief dimly until voltage fell to about .5V. The other supercap
had more internal resistance, so the LED flashed dimly as the joule
thief switched off, then the cap voltage rose, turning it on again.
Quite a strange effect. So I thought about some current limiting
LED driver and gave up, wired the LED straight across the bridge
output, it's better than it was now, and simple too.

Grant.

 

[Grant]

You might find it educational to allow the same circuit to be switchable
drive an incandescent filament bulb or an LED. It is much harder work to
get even a feeble glow out of one of them and very educational for
children. A lot less likely to leave lights on after having to pedal a
bike to power a 60W filament bulb for a while.

You already have enough voltage it is just a case of making it available
to the load in an efficient manner.

Interesting point, apart from me having no little lamps about...

Switch the globe on and the LED will die, leaving said feeble glow
in lamp, nice Power the lamp from the AC side, so it gets all
available juice and no diode drops in the way.

Grant.

 

[Kevin McMurtrie]

Hi there,

I have a small stepper, two windings, no centre tap. Says 4.2 Ohm on
the nameplate. This stepper has an extra gear wheel to get a fairly
fast turn speed.

I wired up two bridges with eight 1N4148 signal diodes direct to a
white 14,000mcd LED. Can get a fairly bright flash out of the
LED.

I'm wondering if there's a better way to connect the windings?

I put a picture of the contraption on:

http://grrr.id.au/image/small-stepper-8-diode-bridge-to-LED.jpg

The circuit is simple, a diode from each of the four stepper lines
to LED anode, and another four diodes going from each line to the LED
cathode.

Wondering if some sort of series winding be better? This is just
something I can give to a friend's kid to he can make some light
and see the components. One may run the thing up one's leg or arm
to create some light too.

Dunno if I should put any over current protection in there as well,
trying to keep it simple.

I did have a capacitor in there but it reduced light output, seems
the spikier the voltage, the better the light output.

Maybe a Joule thief type circuit? Ideas please?

Thanks,
Grant.

As a hand powered toy it's the way you want it now. It's simple and it
works.

If this was for a bicycle you'd maybe want voltage doublers on the
windings then an LED buck regulator module. How the motor works as a
generator over a broad range of speeds will have to be tested.

 

[ehsjr]

...



Exactly, and the kid is quite happy with it, asked if I made it, so I
explained where the stepper came from, how the gear makes it go faster
for more light, and why I added the diodes make the current flow in the
one direction through the LED. So he seemed absorbed with it for a while.

Yeah, I think he liked it At least there's no batteries to go flat.



Was always intended as a handheld toy, now I'm wondering how long the
LED will last with no current limit resistor I didn't get around to
putting say a 1 Ohm resistor in series and measuring voltage across R.

Grant.

Observation, having nothing to do with current limiting:
For something that had to be built with flying leads, it
is pretty damn well built. For the intended purpose, it
seems perfect to me.

Ed