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Harbor Freight 4 LED $7.00

H

Henry Kolesnik

Jan 1, 1970
0
I just got a 4 white LED flashlight that uses 3 AA cells from Harbor
freight. I measured the current at 127 ma and and that leads me to beleive
they are direct wired. Looking inside as best I can it looks like all 4 are
in parallel and connect directly to the 3 cells in series. I think LEDs are
supposed draw a lot less current if they have a dropping resistor. I'm
guessing that a dropping resistor would reduce current draw substantially,
increase led life and not reduce light output significantly. But I can see
were I could easliy install a resistor. I also know just about zero on
leds.
tnx
 
E

Eric Smith

Jan 1, 1970
0
Henry Kolesnik said:
I think LEDs are
supposed draw a lot less current if they have a dropping resistor.

LEDs have a more or less fixed forward voltage drop. If you supply more
voltage than that to them, they draw more current (and produce more
light). But beyond a certain amount of current, they will be damaged.

I'd be surprised if the flashlight has no current limiting resistor.
I'm guessing that a dropping resistor would reduce current draw
substantially, increase led life and not reduce light output
significantly. But I can see
were I could easliy install a resistor.

Light output is nearly a linear function of current. If you increase
the resistance, you will decrease the current, and hence the
light output. This will increase the LED life, but the life was
probably good enough already.
 
F

Fred Bloggs

Jan 1, 1970
0
I just got a 4 white LED flashlight that uses 3 AA cells from Harbor
freight. I measured the current at 127 ma and and that leads me to beleive
they are direct wired. Looking inside as best I can it looks like all 4 are
in parallel and connect directly to the 3 cells in series. I think LEDs are
supposed draw a lot less current if they have a dropping resistor. I'm
guessing that a dropping resistor would reduce current draw substantially,
increase led life and not reduce light output significantly. But I can see
were I could easliy install a resistor. I also know just about zero on
leds.

Sounds like they are using the battery internal resistance to limit the
current. Four LEDs at 30mA/ea gets your ~120mA with Vbatt pulled down to
maybe 3.5V at that current. And it probably has a "good enough" graceful
degradation with battery run down causing the current to taper off
exponentially after a point-reducing battery discharge per use. It does
require the LEDs to be matched to some degree.
 
M

mc

Jan 1, 1970
0
White LEDs require about 4 to 4.5 volts. That is about what comes out of
the AA cells. The internal resistance of the LEDs is probably sufficient.
Newer LEDs have more internal resistance than older ones.
 
W

Watson A.Name - \Watt Sun, the Dark Remover\

Jan 1, 1970
0
Henry Kolesnik said:
I just got a 4 white LED flashlight that uses 3 AA cells from Harbor
freight. I measured the current at 127 ma and and that leads me to beleive
they are direct wired. Looking inside as best I can it looks like all 4 are
in parallel and connect directly to the 3 cells in series. I think LEDs are
supposed draw a lot less current if they have a dropping resistor. I'm
guessing that a dropping resistor would reduce current draw substantially,
increase led life and not reduce light output significantly. But I can see
were I could easliy install a resistor. I also know just about zero on
leds.
tnx

Seems like everything is made for the flashlight that has the profile of
the Mini-Maglite. It has two cells, and fits into all sorts of
holsters, pockets, carriers, etc. So if you get it, or a similarly
sized flashlight, then you're home free. Of course the Mini Maglite has
a halogen bulb, so it sucks. I bought the MagmaLED and Opalec Newbeam
conversion kits for mine, and I'm happy with them. I've seen the three
cell flashlights and I would much prefer that mine not be that long,
three cells is just too long.

Dorcy sells some four LED, two cell flashlights, for under $16. I
bought a couple and They work but the rubber gtrips fall off - no big
thing.

One other disappointing thing about three cells lights is that if they
are direct connected, then you can't use Ni-MH rechargeables in them.
Some flashlights with the V boost circuitry can run on Ni-MHs, possibly
at reduced light output.
 
S

Spehro Pefhany

Jan 1, 1970
0
LEDs have a more or less fixed forward voltage drop. If you supply more
voltage than that to them, they draw more current (and produce more
light). But beyond a certain amount of current, they will be damaged.

I'd be surprised if the flashlight has no current limiting resistor.

It's fairly common that it doesn't.


Best regards,
Spehro Pefhany
 
S

Si Ballenger

Jan 1, 1970
0
I just got a 4 white LED flashlight that uses 3 AA cells from Harbor
freight. I measured the current at 127 ma and and that leads me to beleive
they are direct wired. Looking inside as best I can it looks like all 4 are
in parallel and connect directly to the 3 cells in series. I think LEDs are
supposed draw a lot less current if they have a dropping resistor. I'm
guessing that a dropping resistor would reduce current draw substantially,
increase led life and not reduce light output significantly. But I can see
were I could easliy install a resistor. I also know just about zero on
leds.
tnx

I would assume that LEDs that are now made for flashlights have
built in pulse circuitry to get the brightest output from the
LED. They would include what is necessary to operate at the
correct voltage.
 
W

Watson A.Name - \Watt Sun, the Dark Remover\

Jan 1, 1970
0
Spehro Pefhany said:
It's fairly common that it doesn't.


Best regards,
Spehro Pefhany
--

I agree. The ones that I've seen without a resistor are mostly the ones
that use a CR2016 or CR2025 button cell, basically those keychain lights
that you squeeze. The cells have enough internal resistance to limit
the current.

But alkaline AA cells are capable of delivering more than an amp. I
don't know what the internal resistance is, but it's very low. The
multiple LED Altoids box lights that I've built use 33 ohm resistors,
and I've put as many as 8 LEDs on a set of 3 AA cells, and they're
_bright_. More commonly I do 6 LEDs, each with a 33 ohm resistor, and I
consider that a minimum for a decent source of light.

By using 4 LEDs and no resistors, the light output is probably greater
than my 6 LED lights, but from what I've seen over just a few hundred
hours, the light output from these flashlights will drop off after only
a few hundred hours or less when pushed to this high a current. But it
may take more than a year and several sets of AA cells to put a hundred
hours on a flashlight, and by that time, the warranty has expired.
:-( This is a dirty little secret that no flashlight maker wants you to
know.
 
W

Watson A.Name - \Watt Sun, the Dark Remover\

Jan 1, 1970
0
Si Ballenger said:
I would assume that LEDs that are now made for flashlights have
built in pulse circuitry to get the brightest output from the
LED. They would include what is necessary to operate at the
correct voltage.

Your assumptions are wrong.
 
P

petrus bitbyter

Jan 1, 1970
0
Henry Kolesnik said:
I just got a 4 white LED flashlight that uses 3 AA cells from Harbor
freight. I measured the current at 127 ma and and that leads me to beleive
they are direct wired. Looking inside as best I can it looks like all 4
are in parallel and connect directly to the 3 cells in series. I think
LEDs are supposed draw a lot less current if they have a dropping resistor.
I'm guessing that a dropping resistor would reduce current draw
substantially, increase led life and not reduce light output significantly.
But I can see were I could easliy install a resistor. I also know just
about zero on leds.
tnx

Hank,

Adding a resistor will not be that difficult. A thin piece of two sided PCB
and some handiwork with a fret-saw and a fraise will do the trick. As AA is
pretty small you may need to use two or more SMD resistors in parallel. The
round piece of PCB should be place between a battery and its press spring.

petrus bitbyter
 
W

Watson A.Name - \Watt Sun, the Dark Remover\

Jan 1, 1970
0
petrus bitbyter said:
Adding a resistor will not be that difficult. A thin piece of two sided PCB
and some handiwork with a fret-saw and a fraise will do the trick. As AA is
pretty small you may need to use two or more SMD resistors in parallel. The
round piece of PCB should be place between a battery and its press
spring.

My dictionary says a fraise is "an obstacle of pointed stakes driven
into the ramparts of a fortification in a horizontal or inclined
position".
Which I don't think is what you had in mind. Maybe you could explain.
Thanks.
 
D

Don Pearce

Jan 1, 1970
0
spring.

My dictionary says a fraise is "an obstacle of pointed stakes driven
into the ramparts of a fortification in a horizontal or inclined
position".
Which I don't think is what you had in mind. Maybe you could explain.
Thanks.

He clearly means a strawberry.

d

Pearce Consulting
http://www.pearce.uk.com
 
M

mc

Jan 1, 1970
0
I would assume that LEDs that are now made for flashlights have
And your proof is...? ;-)

I don't know about *his* proof, but I've never seen such things on the
component market. They'd be handy if they existed. I've seen LEDs with
built-in flashers and with built-in current regulators to run from much
higher voltages.

Also, if pulsing were going on, you'd see stroboscopic effects when you
moved the flashlight quickly, wouldn't you?
 
S

Spehro Pefhany

Jan 1, 1970
0
spring.

My dictionary says a fraise is "an obstacle of pointed stakes driven
into the ramparts of a fortification in a horizontal or inclined
position".
Which I don't think is what you had in mind. Maybe you could explain.
Thanks.

A google search comes up with "fraise toestel", but it's not clear to
me what exactly it does. Cut a donut in the PCB?


Best regards,
Spehro Pefhany
 
J

James Meyer

Jan 1, 1970
0
It's fairly common that it doesn't.

If you think about it, the batteries do have an equivalent series
resistance and the LEDs are not perfect voltage clamps either. There IS a
series resistance even though there is no discrete resistor in the circuit.

Jim
 
S

Spehro Pefhany

Jan 1, 1970
0
If you think about it, the batteries do have an equivalent series
resistance and the LEDs are not perfect voltage clamps either. There IS a
series resistance even though there is no discrete resistor in the circuit.

Jim

Exactly. That's why they work. Maybe not as perfectly as some would
like, but good enough to sell.

OTOH, an LED backlit LCD graphics display I have uses some
sophisticated white LED driver chip arrangement. The backlight snaps
on as the voltage is ramped up, almost like a fluorescent.


Best regards,
Spehro Pefhany
 
R

Rich Grise

Jan 1, 1970
0
A google search comes up with "fraise toestel", but it's not clear to
me what exactly it does. Cut a donut in the PCB?
Heck, I'm still stuck on 'fret-saw'. )-;

Thanks,
Rich
 
F

Frank Bemelman

Jan 1, 1970
0
Watson A.Name - "Watt Sun said:
spring.

My dictionary says a fraise is "an obstacle of pointed stakes driven
into the ramparts of a fortification in a horizontal or inclined
position".
Which I don't think is what you had in mind. Maybe you could explain.
Thanks.

Milling cutter. (Dutch -> Frees).
 
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