Need some advice my Li ion powered, pwm dimmed led light circuit please!!

[Jules Arundell]

Hi all,

I am working on a lighting project for my a level product design coursework and I am in desperate need of some advice/help on how to build the circuit. It involves powering and dimming a 300mm 12v strip of leds that are 14.4 wpm/0.3 = 4.3w, all in a very small space of 35x35x90mm. At the moment I am planning on using a 3.7v 500mAh li-ion battery (could I connect multiple of these in series or parallel??) connected to a li ion battery charger (that can charge the battery while it powers the components). The voltage will be stepped up to 12v using a boost converter, these seem to be widely available in 3.7v-12v but not so widely available in lets say 7.4v-12v or 11.1v-12v; maybe is there an alternative to a boost converter that would fit in this space? I have decided to use PWM to dim the lights instead of a potentiometer to get a Better range of brightness. however I don't know if the one I have chosen is compatible with my circuit (see component spec below). Also I don't know if I need a buck converter to drop the voltage back down before it goes back into the battery.
see drawing of my lamp and my rough circuit plan below.

I would really appreciate any advice anyone could give me to get this circuit to work as my deadline is aproaching fast and I need to order these components so I can build the light.
Thank you

see sources of my components, drawing of my lamp, PWM dimmer spec and my rough circuit plan below:

sources for my components:
Led Strip: Maplin, no link available apparently
Li ion Battery: https://www.adafruit.com/products/1578
Battery Charger: https://www.adafruit.com/products/259
Boost converter: http://www.ebay.co.uk/itm/like/2718...=9045991&device=c&campaignid=207297426&crdt=0
PWM dimmer:http://www.ebay.co.uk/itm/like/1824...=9045991&device=c&campaignid=738474636&crdt=0

 

[donkey]

so many things.... where to start...
number 1 and foremost. Welcome young adventurer your time here will be most wisely used

ok lets move onto your design.
I understand you want to make a 12vault LED strip with in built charger. I understand you have an idea.... of sorts but now I need to educate you on a couple of things.
first and foremost you say you are using a lipo battery... that's awesome. THE SECOND YOU PUT MORE THAN 1 IN SERIES OR PARALLEL YOU NEED A NEW CHARGER.
second what do you want to have them in, series? parallel? or both? all are possible BUT if you parallel them you will get more amps... if even 1 of the cells dies and you try charging them while still in parallel it could end up bad.
in series they will get you more voltage so less need for a voltage booster.BUT then the charger needed is different again as you have 11.1volts in total and not the 3.7v
if you are doing both then you have both of those issues...

now PWM/Potentiometer is simple... PWM pulses the battery and SAVES ENERGY.... that simple

this thing about a buck converter is well........ just wrong.... get it out of your head.

ok and last but not least you say this is for a course of some sort???? what course? if its an electronic course then it might be best to resit the whole thing because DC electronics has to be the easiest thing on the planet to grasp and by the looks of it you haven't gotten there. when you move on to opamps, digital electronics and, microcontrollers and AC theory your poor little head might just explode.

 

[Audioguru]

If you try to charge the battery while the battery is powering the LEDs then the charger will not know how much if any power is going into the battery then the battery might not charge.