need help figuring out current of..

[Evilsizer]

the LED setup im running, just messing with these cree led's john sent me. got 20 all in parallel, im aiming for 20mA to each LED. if i were to do that then i should see a total of 400mA on my DMM right? well right now i have them getting a total of [email protected], using a 4s AA holder. right now my setup for limiting current is two fixed 15ohm+ reo 25ohm in series.

being trying to find the most efficient design out there for current limiting. this way im doing it seems the most basic way of doing it. the question is how efficient is it and is it worth looking for something more efficient?

 

[bobrez]

Grab a cheep driver from dx, based on your battery type an run them at 350ma in parallel. This should be most efficent :wave:

 

[Evilsizer]

link for DX?

 

[Curt R]

In parallel, only current is added not and not voltage. If run in series than voltage is added and not current.
The problem with running LEDs in parallel is that every LED has a different voltage drop requirement,
that means that one or more LEDs may have a lower voltage which will allow more current to flow through
it than the others. When limited to a max driver current of 400 mA, that LED will see most or more current
than the others. If it is an XP LED that will not be a problem, just that the other LEDs will be less bright.
If it is a 5 mm LED , and then the next one, and so forth. When using LEDs in parallel a current limiting
resistor is used with each LED. The value of the current limiting resistor is determined by the supply
voltage to the LEDs.

When measuring current in a circuit use a 0.1 ohm 3 or 5 watt 1 % resistor in between the power supply
and the LED. Measure the voltage drop across the resistor and use Ohm's law to give you an accurate
current reading. 10 different DMMs will give 10 different readings if using the current measuring feature
that they provide.

Curt

 

[bobrez]

link for DX?

Looking for a 350ma driver was tough I only found 700ma for batt power, it might take a little more searchin, sorry
Did find AC mains driver, but be careful with this! You have to plug it into AC
http://www.dealextreme.com/details.dx/sku.13554

 

[MikeAusC]

link for DX?

Posting links here to DX is not allowed - though I can't see anything in the Forum rules that says so.

I personally won't be putting in any orders to DX for a while. They have a serious problem where lots of people, including me, are complaining on their Forum that orders are not being delivered for weeks, even though the descriptions still say "Typically ships in 4 to 7 days".