Led falshlight with magnetic powering?

[terry]

A friend has just received one of those flashlights which use LEDs.
LEDs for lighting now very common now; so that was no surprise.

The flashlight has some sort of 'charging system' inside whereby one
shakes the flashlight and what appears to be a loose magnetic goes back
and forth through some sort of cylindrical coil.

This unit also contains what appears to be a low voltage capacitor of
unknown value. Thus far as a magnetic induction charging system with
capacitive storage everything seemed to make sense.

But: This flashlight also contains two AA or AAA cells (can't recall
which) which are NOT of the rechargeable type.

Any hints/info as to how these things operate; also why the non
rechargeable alkaline cells?

We also speculated that the longer one shook the flashlight the more
energy (coulombs etc.) would be stored in the capacitor? True/untrue?

Appreciate any comment.

 

[John Popelish]

A friend has just received one of those flashlights which use LEDs.
LEDs for lighting now very common now; so that was no surprise.

The flashlight has some sort of 'charging system' inside whereby one
shakes the flashlight and what appears to be a loose magnetic goes back
and forth through some sort of cylindrical coil.

This unit also contains what appears to be a low voltage capacitor of
unknown value. Thus far as a magnetic induction charging system with
capacitive storage everything seemed to make sense.

But: This flashlight also contains two AA or AAA cells (can't recall
which) which are NOT of the rechargeable type.

Any hints/info as to how these things operate; also why the non
rechargeable alkaline cells?

We also speculated that the longer one shook the flashlight the more
energy (coulombs etc.) would be stored in the capacitor? True/untrue?

Appreciate any comment.

I would bet that the electronics and magnet are dummies and
the LEDs run strictly on the batteries. How long will you
be able to resist taking it apart to find out?

 

[Glenn Ashmore]

Don't know about the batteries. Mine is just a capacitor, coil and sliding
magnet. Shake it for a few seconds so the magnet inducts a current in the
coil which charges the capacitor up enough to keep the LED lit for 4 or 5
minutes. Nothing like as good as my Coast Lenser V but because you never
have to worry about dead batteries it is great for the glove compartment or
a survival bag.

You would have to shake it for days to charge up a Nimh battery.

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

 

[Don Bruder]

I would bet that the electronics and magnet are dummies and
the LEDs run strictly on the batteries.

Maybe, maybe not, John...

I've seen the "two for five bucks" units that have a couple CR2032s in
'em. I've also scrapped them because the batteries died and the "shake
system" was about as useful as tits on a boar hog - shake for a minute,
get 30 seconds of weak light.

I've also seen the type that have *NO* batteries - And still have that
one sitting on the windowsill above the bed. Works great. hit the
switch, and it's dead? No problem... A couple shakes back and forth, and
it's operational, even if rather dim. A few more, and it's nice and
bright, and stays that way for a surprisingly long time. It's no 8-cell

How long will you
be able to resist taking it apart to find out?

The first one I encountered (the two for five bucks version) didn't make
it out of the store parking lot intact

I was able to hold out a bit longer with the current one.

For the OP:

Your idea of "more shake = more energy" is correct, up to a point. Shake
it long enough, and if it's not a "dummy" version, you'll eventually hit
the limit of the capacitor. Dunno what the value of the cap is, but
whatever the number happens to be, it has a definite "I can store this
much energy and no more" upper limit to it. Keep shaking beyond that
point, and you're going to start charging (or at least, attempting to -
they may not be able to TAKE a charge, depending on their condition) the
batter(y/ies) with the excess. If the batteries are able to take the
charge, no problem. If not, you're doing nothing but wasting effort -
basically just turning "lots of shaking" into "a little heat".

*ALL* batteries are rechargable, *TO AN EXTENT*. The problem is that not
all *TYPES* of batteries take well to being recharged at the rates "Joe
Consumer" demands. Carbon cells and alkalines can be "topped up" a bit,
if you do it carefully (Very low current over a long time) but don't
expect "like new" life out of them, and if you get the current too high,
expect them to bulge, leak, and/or explode. "Designed-to-be-rechargable"
batteries like NiCds and similar, use a different chemistry, which is
much more "friendly" to being charged, and can cope with the shorter
charge cycle (and accompanying higher current rate) that's required to
make them "consumer acceptable".

Case in point:
In years gone by, I ran a walkman for almost a year of 6-8 hours a day
use on three pairs of AA Duracell batteries - Two sets were in a
slightly tweaked (An extra resistor that, according to my calculations
at the time, took the charge rate down to roughly C/200) NiCd recharger,
with the third set in the walkman, rotating them whenever they showed
signs of starting to die. Part of the secret is to not run them
*COMPLETELY* dead. The other part is that you have to be able to deal
with the "charging these things takes *FOREVER*" concept. At the start
of the experiment, about 16 hours of charge-time on the two sets in the
charger, plus "whatever was left" on the set in the walkman at the end
of the previous day would give me just a hair under 12 hours of run-time
on the walkman. By the end of it, the same charge time would only give
me about 6-7 hours of total run-time.

 

[terry]

Don't know about the batteries. Mine is just a capacitor, coil and sliding
magnet. Shake it for a few seconds so the magnet inducts a current in the
coil which charges the capacitor up enough to keep the LED lit for 4 or 5
minutes. ......................... snip .......................

..
Yes that's what we figured ................... maybe even up to 8 or 10
minutes maximum?

But with all the excitement of opening other presents the methodical
approach of actually timing how long it would light before the energy
stored in the cap. was used up kinda got lost!

But still trying to figure out why the thing contains two seemingly
'ordinary' alkaline cells?
It certainly seems to use the induced energy.

BTW I do recall some sort of hand cranked (one hand thumb and fingers
etc.) flashlight probably around 1938 and of German manufacture IIRC.
It only lit as long as the mechanism inside was whirring as you
continually squeezed it in you hand.

Interesting because today there have been such major improvements in
magnets and capacitors that what would have been impractical back then
can be incorporated into a few dollars flashlight! The improvements in
magnetic materials (and glues etc.) made possible loudspeakers that do
not require the multi turn energising coils (also used as smoothing
chokes) as previously.

 

[terry]

.
Yes that's what we figured ................... maybe even up to 8 or 10
minutes maximum?

But with all the excitement of opening other presents the methodical
approach of actually timing how long it would light before the energy
stored in the cap. was used up kinda got lost!

But still trying to figure out why the thing contains two seemingly
'ordinary' alkaline cells?
............................ then snipped ..............................

..
Terry writes further .................... yes as Bruder mentions;
'recharging' ordinary alkaline cells etc.

I always took that to be a case of sort of reactivating or maybe even
slightly reversing some part of the chemical action of the primary
cell?
So maybe these 'shake and bake' flashlights do a bit of both; charge up
a capacitor and with a bit of the energy going to 'reactivate' or at
least prolong the life of very ordinary alkaline cells?

Any idea of the 'efficiency' of an induced energy flashlight? For
example if I use the energy contained in one bottle of beer (or glass
of good red wine) both possibly useful comparisons for this time of
year, maybe, maybe not, to shake the flashlight, how many calories or
coulombs of light energy will I get out?

Academic question; the idea in this instance being more the convenience
and immediate availability of a light source while avoiding the long
term storage and or deterioration of either storage or primary cells.
But I guess if I trailed one behind the sailboat bobbing along in the
wake or hung it in the cab of the pickup so it jiggled nicely (some
bumpy roads here too!) it would be usefully charged!

Many thanks for the discussion.

 

[Don Klipstein]

I've seen the "two for five bucks" units that have a couple CR2032s in
'em. I've also scrapped them because the batteries died and the "shake
system" was about as useful as tits on a boar hog - shake for a minute,
get 30 seconds of weak light.

I have seen some $2 units in dollar stores where the "magnets" are
pieces of plain steel rod without magnetism, the coil's leads are soldered
together onto one spot on the PCB, the only semiconductor is the LED, and
the only energy storage device is the pair of CR2032 cells.

It has been noted that not all $2 dollar store shake flashlights are
such frauds.

I have seen others (at hardware stores for more than $2) with a switch
that selected generator power or battery power.

- Don Klipstein ([email protected])

 

[Michael A. Terrell]

Don't know about the batteries. Mine is just a capacitor, coil and sliding
magnet. Shake it for a few seconds so the magnet inducts a current in the
coil which charges the capacitor up enough to keep the LED lit for 4 or 5
minutes. Nothing like as good as my Coast Lenser V but because you never
have to worry about dead batteries it is great for the glove compartment or
a survival bag.

You would have to shake it for days to charge up a Nimh battery.

Wouldn't that make them go blind? ;-)


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[Don Bruder]

I have seen some $2 units in dollar stores where the "magnets" are
pieces of plain steel rod without magnetism, the coil's leads are soldered
together onto one spot on the PCB, the only semiconductor is the LED, and
the only energy storage device is the pair of CR2032 cells.

It has been noted that not all $2 dollar store shake flashlights are
such frauds.

I have seen others (at hardware stores for more than $2) with a switch
that selected generator power or battery power.

- Don Klipstein ([email protected])

Yep. The one I've currently got isn't that fancy, but it's *VERY*
clearly operating "as-advertised" - Two diodes, a cap, the LED, and the
coil, plus a switch, and of course, the magnet. Unless they've managed
to cleverly disguise a battery as a capacitor, it really does do what it
claims, without "cheating", and reasonably well. LIke I said in the
other message, it isn't an eight-D Maglite, but... <shrug> It was never
intended to be.

 

[Michael Black]

Yep. The one I've currently got isn't that fancy, but it's *VERY*
clearly operating "as-advertised" - Two diodes, a cap, the LED, and the
coil, plus a switch, and of course, the magnet. Unless they've managed
to cleverly disguise a battery as a capacitor, it really does do what it
claims, without "cheating", and reasonably well. LIke I said in the
other message, it isn't an eight-D Maglite, but... <shrug> It was never
intended to be.

I was playing with making one, sort of. I used a stepping motor with
some diodes feeding an "ultracap" that I took out of a VCR. The light
didn't really sustain itself for long, but you could see the capacitor
charging up. Turn the knob, and there'd be some light, and turn it enough
and the capacitor would get charged up.

SOme problems were that I could only find one "ultracap", though I know
I've saved some more out of things. And most of the stepping motors I
had were not conducive to easily adding a knob, so I couldn't play with
different motors easily. When the spring comes, I'll remember and keep
an eye out for junked VCRs and other things that might have "ultracaps"
in them, and parallel them for longer power.

I have one of the commercially made crank ones. And it worked out of
the box two or is it three years ago. I can't remember if I tried it
without cranking, but there was light and of a reasonable length of
time, from the moment I first tried it. That isn't likely the case
if it's a chargeable battery in there. It's never gone dark, though
I admit I don't use it that much (it is handy to know it's there and I
don't have to worry about whether the batteries will be working). A
minute of cranking, and it's back to full brightness.

Michael