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mike[_22_]

On 2/24/2017 10:45 AM, wrote:
On Friday, February 24, 2017 at 1:16:23 PM UTC-5, Pat wrote:
On Fri, 24 Feb 2017 09:36:12 -0800 (PST), "
wrote:

On Thursday, February 23, 2017 at 2:25:19 PM UTC-5, mike wrote:

Might want to check that math.

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
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.)

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

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. ;-)