DC Timer as a primitive Battery power-pack OverLord

[BillBlake]

A fellow was asking about working with LED Lights that have USB plugs for their power.
He was concerned with making up a power-pack using  some high dollar Lithium ion batteries and was
talking about "just winging it" as to when he disco-ed the power-pack and pluged into another high dollar pack.

I didn't want to get into the subject very deeply but did run a little bit since I'm updating my LED bookmarks,
documents and what have you. Also looking for some good lights at a good price. Here it is.

<snip>
 
The myth of the 5 volt LED
 
A commonly encountered question on message boards and in my email inbox deals with the elusive “5V LED,” and
goes something like this.

 I have a 5V blue LED, can I hook it directly to the 5V supply in my computer?

 or alternately:

 I hooked up my 5V LED directly to my computer's PSU, why was the magic smoke released?
 
The fact is, there are simply no LEDs with a forward voltage of 5V. So how does this confusion arise?
There are three possibilitiies.
We'll go over them all.
 
Type one: confusion about specs
 
The specs on LEDs often include a reverse voltage spec, and 5V is not an uncommon value to see for this.
But this is not an operating voltage, this is the maximum reverse bias voltage you can apply before the LED fails.

This sort of confusion accounts for most of the “sightings” of 5V LEDs in the wild.
 
Type two: ambitious claims by the seller
 
The fine folks at Radio S*ack offer a 300 mcd blue LED (part number 276-311), for which they claim a forward
voltage of 5V, 6V max.
Their website also lists the wavelength as 430mm [sic]. This (430 nm) is a short wavelength blue compared to the
more common
470nm blue LEDs available now.

Most makers of 430nm blue LEDs use GaN on a SiC substrate. These LEDs do actually seem to tolerate being
driven hard, for some length of time,
and 30 mA drive currents are listed in several manufacturers datasheets for this type of LEDs.

But I find that keeping to 20mA drive current or below is the soundest way to ensure the long life of your LED.
Hooking an LED directly to any voltage source is a poor choice, regardless of specs.
 
Type three: LEDs with integrated resistors
 
They are far more common in 12V ratings (for vehicle applications), but you will occasionally find 5V rated devices.
These are usually clearly labeled “LED with integrated resistor.”

Or as one German site poetically puts it: “Die bei uns angebotenen 5V-LEDs besitzen einen
integrierten 5V-Resistor, der (winzig klein) direkt im Epoxygehäuse der LED vergossen ist.”

 [prev: Lumileds announces new Luxeon offerings]
[next: Surface mount LEDs]
 
http://led.linear1.(ORG)/myth-of-the-5-volt-led/
 
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I like an outfit that can blow their own horn - if they have a lot of horn to blow.
Just started trying to get an update on LED Lights and 5 Volts may work well for (4) 1.2 Volt Battery Cells that will range
between about 5.6 Volts (H) to 4.4 Volts (L) depending on the SOC.

The batteries will hopefully not get run into the ground (how some Likes it) or the Voltage could drop a good bit lower.

A fairly inexpensive DC Timer will act as the Low Tech 'Battery OverLord'

after each charge in case you get busy and become abusive.
Before the battery abuse can start you just get cut off like a criminal and get left in the dark. 
No idea how good this info above is but I like the writer's style.
 
Bill Blake