help with 21 led power.

[dog812]

Hi .. i make led hula hoops for my gf and her friends.. but i would like to be able to make them cheaper for them... You can see how i make them on my website.. led hula hoop .com
I have been looking into joule thiefs..
Can i use one for my application.. 21 RGB LED's @ 3.6v / 30ma
I would like to power them with a single AA rechargeable.

Do i need different items for the joule thief? larger resistors? larger ferride? etc...
How long will the led's stay lit for on a single full charged 2450mah battery...
etc... any info would be awesome.

 

[Oznog]

Well that's a lot to ask from an AA cell, about 2 amps.

AFAIK the JT won't behave with the load being switched around like that. I'm assuming you've got RGB LEDs with internal fader/blinkers? The current on each one will vary and that'll probably cause the JT's voltage to vary quite a bit.

There's the AA-sized lithium-ion. The benefit there would be not needing the voltage boost when fully charged, but the large voltage variation between full and empty- and it being below the specified voltage for the last 30% or so of capacity- can be a problem.

 

[Illum]

do0d! we just finished a thread like this
21 LEDs for a Hula hoop, see thread: 21 LEDs from 2xAA batteries
the thread op had this to say

I'm basically making a light tube (lit hula hoop), as opposed to a flashlight, which is why the array

Where, may I ask did you get the idea from? you are concidentially the second person on the forum asking how to drive 21LEDs for a Hula-hoop project:thinking:

 

[dog812]

... Duplicate

 

[dog812]

Wierd.. i have been selling these hoops for about 5 months now..
I guess they are starting to catch on..
But its cool anyway.. i found a guy that is building me a circuit, like a Joule thief mixed with a regulator.. so i can use 1 AAA battery that will last as long as my 4 AA's do now.. ill post some info when i get it all working.

 

[Illum]

:twothumbs