Pat wrote:
On Fri, 24 Feb 2017 10:45:18 -0800 (PST), "
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

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



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 **** off an Engineer!

They don't get mad.

They don't get even.

They go for over unity! ;-)