Batteries make flashilight hot.

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I have one of thoe little 2.5" LED flashlights, that have 9 small LEDs
and use 3 AAA batteries.   It's like the ones that Harbor Freight
sometimes gives away free, same size, but nicer.  

The guy I bought the first one from said it would run for days on one
set of batteries, but I forgot that it was still on and i put it in my
pocket and an hour or two later, I noticed it was on because it was
warm.  

It's still really bright, but if it's noticeably warm, how long can the
baterries really last?   Certainly not two days. ?  


I once, recently, forgot the screen was lit on my 5.5" smart phone and
only noticed because it felt warm in my pocket.    

It's got a proximity sensor but I don't remember what it's supposed to
do.  

Re: Batteries make flashilight hot.
On 02/23/2017 01:47 AM, micky wrote:
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YEAH, WELL I HAD MY LED LIGHT BULB IN MY KITCHEN HOOD ON ALL DAY AND IT  
WAS TOO HOT TO TOUCH SO WHAT'S YOUR POINT?

Re: Batteries make flashilight hot.
On Wednesday, February 22, 2017 at 8:48:12 PM UTC-5, micky wrote:
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The heat is from the LEDs, not the batteries, and no, the batteries will no
t last indefinitely. I would guess (SWAG) that each LED will run about 50 m
a. So you are pulling 450 ma, or thereabout per hour. If your AAA batteries
 are middle-of-the-road 1,000 MAH, you have a base of 3000 MAH, so, about 6
-7 hours +/- or so. Under normal use, that is 'days'.  

Peter Wieck
Melrose Park, PA

Re: Batteries make flashilight hot.
On 2/23/2017 4:58 AM, snipped-for-privacy@aol.com wrote:
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not last indefinitely. I would guess (SWAG) that each LED will run about  
50 ma.

So you are pulling 450 ma, or thereabout per hour. If your AAA batteries  
are

middle-of-the-road 1,000 MAH, you have a base of 3000 MAH, so, about 6-7  
hours

+/- or so. Under normal use, that is 'days'.
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Might want to check that math.


Re: Batteries make flashilight hot.
On Thursday, February 23, 2017 at 2:25:19 PM UTC-5, mike wrote:

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OK. 50 x 9 = 450. 9 LEDs at 50 ma each.
3 x 1000 = 3000. 3 cells at 1000mah each.
3000 / 450 = 6.67. At 450 ma, that will go 6.67 hours.  

The reality is probably different as all the shots/assumptions are center-mass. If the LEDs are 100ma outliers, if the cells are 1.4mah outliers, things do change, of course.

Peter Wieck
Melrose Park, PA  

Re: Batteries make flashilight hot.
On Fri, 24 Feb 2017 09:36:12 -0800 (PST), " snipped-for-privacy@aol.com"

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3 cells at 1000 mah each do NOT give you 3000 mah.  They give you 1000
mah but at a higher voltage (4.5 vs 1.5).  If you use mwh (watts)
instead of mah (amps), then you can add them.

(If the cells are wired in parallel instead of series, then you are
correct, but that isn't very common.)



Re: Batteries make flashilight hot.
On Friday, February 24, 2017 at 1:16:23 PM UTC-5, Pat wrote:
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The three similar lights I have, they are in parallel. Which is why I probably wrongly assumed these were as well.  

Funny thing, these types of lights are often give-away items at Solar Energy conferences - I have been to my fair share, and how they came into my hands. Otherwise I would not touch this cr*p on a bet.  

Peter Wieck
Melrose Park, PA  

Re: Batteries make flashilight hot.
On Fri, 24 Feb 2017 10:45:18 -0800 (PST), " snipped-for-privacy@aol.com"

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I just checked 3 of mine...  Two give-aways and one UV of similar
design.  All three have the AAA batteries connected in series.  That
got me wondering how the LEDs are wired, but I was too lazy to take
them apart.  All have 9 LEDs so I will guess 3 sets of 3.  Is 4.5v
enough to power a 3 LED string?  Just went to look it up and the
answer to my own question is "no".  UV and White LEDs typically have a
Vf of 3.3 volts.  So, all 9 are in parallel with their own current
limiter?  If so, why 9?  Is there a cheap IC that supports 9 LEDs?  If
anyone knows, please educate us.

Pat
  

Re: Batteries make flashilight hot.
Pat wrote:
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    I cut open one of the Harbor Freight nine LED flashlights that was  
damaged. All nine LEDs are in parallel, and all three cells are in  
series. They use the internal resistance of the cells to limit he current.

    The forward voltage of a white LED is typically 3.7 to 4.2 volts, so  
parallel cells would require a boost converter which would double the  
cost of the electronics in a flashlight.

    BTW, the Harbor Freight flashlight will slip into a cheap microphone  
boom for a handy bench light.

  
Mic-Arm-Stand-Microphone-Suspension-Boom-Scissor-Holder-For-Studio-Broadcast

http://www.ebay.com/itm/272436300096

--  
Never piss off an Engineer!

They don't get mad.

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Re: Batteries make flashilight hot.
On Fri, 24 Feb 2017, Pat wrote:

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Are you talking about the really cheap LED flashlights?

I've taken some apart, and I don't see anything but the LEDs.  So they  
have to be in parallel, and rely on the bettery itself to supply some  
level of series resistance.

The cheap ones sometimes aren't even soldered together, just sort of  
pressed together, which may account for why some of the LEDs don't light,  
bad contact.  Of course, these are just white LEDs in some package, not  
"chip" LEDs like in better LED flashlights and LED light bulbs.

   Michael


Re: Batteries make flashilight hot.
In sci.electronics.repair, on Fri, 24 Feb 2017 18:47:01 -0500, Michael

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Sometimes one or two of the bulbs go out, so I think that also means
parallel.  
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Re: Batteries make flashilight hot.

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If they're in parallel, then they almost certainly aren't driving the
LEDs directly... a blue LED (with or without a white phosphor)
requires more than 3 volts in order to conduct.

So, if they're in parallel and are feeding only 1.5 volts into the LED
head, there is probably a voltage-boost circuit (e.g. a "Joule Thief")
which is stepping up the voltage before it reaches the LEDs.

And, the step-up comes at a cost.  If the Joule Thief has to triple
the voltage before it feeds the LEDs, and the LEDs are drawing a total
of 100 mA at that voltage, then the Joule Thief will be pulling 300 mA
or more out of the batteries.

There ain't no free lunch, alas.

A simple series arrangement is less expensive, but it'll end up
wasting some power in a current-limiting resistor (unless the
flashlight makers go _really_ cheap) and the flashlight will slowly
dim as the battery runs down.  A step-up circuit can feed a fairly
constant current through the LEDs until the batteries are almost
completely exhausted, and it allows for a "variable brightness"
feature (pulse-width-modulate the LEDs, or step up to a lower voltage
which results in a lower current).



Re: Batteries make flashilight hot.
On 2/24/2017 10:45 AM, snipped-for-privacy@aol.com wrote:
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It's certainly possible, but it's a bad design tradeoff, and a safety
hazard, to put 3XAAA in parallel.
I've never seen one that way.

Even if they were in parallel, you'd need about 3X the led current
from the batteries, so your math is still questionable.
watts from battery x efficiency = watts to led.

The cheapest lights use 3XAAA in series connected directly to the
parallel combination of LED's.
They ship with "heavy duty" batteries and the series resistance
of the batteries limits the current.  Alkaline batteries will overheat
the LED's.  Now you know why the LED's start to flicker after a while.

If you try to run one off a 18650 you'll burn out the leds,
even though the 4.2V of the cell is less than the nominal
4.5V of three AAA cells.  I had to put 1.5 ohms in series to make
it work.

If are really bored, you can cut two FREE Harbor
Freight lights in two and solder the parts back together
(well, they're aluminum so use something like Welco 52)
to make one longer light that accepts a 18650.  Don't forget the
series resistor.
This made a lot more sense back before you could buy a
single AA zoom flashlight for $2.

If you take out 8 of the 9 LED's and make the
resistor larger, it makes a great
emergency light that will run forever during a power outage.
Just my luck...we haven't had a power outage since I built it. ;-)


Re: Batteries make flashilight hot.
wrote:

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Did you notice that almost all such flashlights are made from
aluminum, not plastic, which would be cheaper?  That's because
aluminum makes a good heat sink to get the heat away from the LED's.
LED's loose output and efficiency when hot, so it pays to keep them
cool.  The COB style of LED mounting is quite common in larger
flashlights, which offer a heat conductive path from the LED to the
aluminum heatsink case.

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No, it won't run forever.  AAA alkaline batteries are good for
1000ma-hr each.  At something less than 4.5V for 3 batteries, that's
4.5 watt-hrs.  Commodity LED's generate about 50 lumens/watt, so if
your Harbor Freight flashlight managed to belch 15 lumens, it will
consume 0.3 watts.  Runtime is therefore an optimistic:
  4.5 watt-hrs / 0.3 watts = 15 hrs.
It's probably less because I didn't bother throwing in losses in the
current source, decrease in battery voltage as it runs down, and
heating effects.  But, it should give you a ballpark guess as to how
long it will run.  My guess(tm) is it will run about 8 hrs with a new
set of batteries.

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If your smartphone as a battery usage graph, like all Android phones,
you'll find that it also has a list of which applications are sucking
the most power.  The backlighting for the OLED screen is invariably
the highest.  If you don't talk on your phone, and don't run any apps,
the battery life of your phone will be totally dependent on the
brightness setting and efficiency of the OLED display, which is about
the same 50 lumens/watt as your white LED.  (Yes, I know there are
press releases for >100 lumens/watt, but those are under laboratory
conditions).

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Never heard of it.  Maker and model number?

--  
Jeff Liebermann     snipped-for-privacy@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
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Re: Batteries make flashilight hot.
wrote:
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No brain function before my morning tea.  That's wrong.  There is no
backlighting in an OLED display.  That should be the LED "screen"
power consumption, not backlighting power consumption.  
<https://www.howtogeek.com/244748/how-to-see-which-apps-are-draining-your-battery-on-an-android-phone-or-tablet/

--  
Jeff Liebermann     snipped-for-privacy@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
We've slightly trimmed the long signature. Click to see the full one.
Re: Batteries make flashilight hot.
snipped-for-privacy@cruzio.com says...
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to do

Isn't it just to switch off the screen and touch sensitivity when  
adjacent to your head so your ear doesn't swipe at random?

Mike.



Re: Batteries make flashilight hot.
In sci.electronics.repair, on Thu, 23 Feb 2017 19:41:35 -0000, MJC

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Yeah, that's it.  I guess I thought the screen would go off in my front
pants pocket too, light weight pants,  but it didn't.  

I hadn't relied on that, just forgot, and I won't rely on it in the
future.    I guess my pants pocket won't swipe anything ilke my ear
could.  


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Re: Batteries make flashilight hot.
On Wednesday, February 22, 2017 at 5:48:12 PM UTC-8, micky wrote:
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The internal resistance of the batteries, and the internal resistance of
the LEDs used, is very much a part of the design of those flashlights.
Both the LEDs and the batteries do get warm in normal operation,
and (as you suspect) it's likely that a fresh set of batteries will last
well under a day of ON operation;  Duracell AAA claims 3.5 hours at 1/4W  
output, so a three-cell light could deliver over half a watt for a useful
amount of time; hours, not days.

<https://d2ei442zrkqy2u.cloudfront.net/wp-content/uploads/2016/03/MN2400_US_CT1.pdf

Re: Batteries make flashilight hot.
wrote:

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I buy these at Walmart for $1 each. I use them a lot. I have left them
on overnight and they still work, but that greatly shortens the battery
life. If they are not left on for long periods of time, they last weeks
and that is being used almost daily. For a buck each, I usually buy 5 at
a time and that keep me with working flashlites for a few months. I keep
one in the car, one in the truck, one in the house and a few other
places.  

Unless I can buy batteries real cheap at some dollar store, (like 8
batteries for a buck), it's not worth replacing the batteries. I just
toss them and buy more flashlights which cost $1 WITH batteries.  
I have never had any of them get hot or cause any problems at all. I did
have a few with switch problems, but very few. Since I have plenty ones
with dead batteries, I just swap the batteries from one with a bad
switch to one that still works.  

I have saved the LEDs from a lot of them that I toss. Not sure why, but
some day they might have a use... I guess these are just meant to be
used and disposed..... But I have replaced the batteries a few times
too.

Either way, they are 1000X better than the old flashlights I grew up
with, that had very short battery life and almost always developed
switch problems after a month or less.  




Re: Batteries make flashilight hot.
In sci.electronics.repair, on Fri, 24 Feb 2017 15:53:52 -0600,
snipped-for-privacy@tubes.com wrote:

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I don't think I had had that either, which is why I posted.   Of course
maybe I'd never left it on so long before.  

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I don't have as many as you, I've had maybe 10 total and 2 or 3 have had
the switch fail after very few uses.  I  expect the others to fail any
minute....

That's caused me to think, Don't wear out the switch, leave it on,
And that's what led to my leaving it on when I put it in my pocket!

Which might be the only reason it was warm.  

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