Driving 20 leds with battery

[iteoschi]

The best way to test is to buy 20 3mm leds, solder them together in a serial/parallel configuration and test with a variable bench power supply. Then you can see if they can do the job and how much current they need for it.
When you know the amount of current for the leds, you need to look at the driver and how good efficiency you can get.
It is much easier to select batteries when you know how much power you need.

Yea i think that's the shortest and best way to see real consumpitons based on how much light i need. Have you got any suggestion on good quality, efficient leds?


Talking about batteries, are this batteries any good? (http://www.batteryspace.com/sanyo-l...7-5-aa-size-3-47wh-0-28---un-38-3-passed.aspx)
If not, are there good 14650-14500 batteries that do not cost a fortune?

 

[HKJ]

Yea i think that's the shortest and best way to see real consumpitons based on how much light i need. Have you got any suggestion on good quality, efficient leds?

Not really, the ones I used was from Ebay without any name on them.

Talking about batteries, are this batteries any good? (http://www.batteryspace.com/sanyo-l...7-5-aa-size-3-47wh-0-28---un-38-3-passed.aspx)
If not, are there good 14650-14500 batteries that do not cost a fortune?

Sanyo is good quality. You get most capacity in 18650 size, there you can get above 3200mAh in a single cell. When using LiIon cells, remember to check the discharge curve, most cells starts at 4.2 volt and stops at 3, 2.75, 2.5 or (in a few cases) 2 volt, you might not be able to use them all the way down to the lowest voltage. You can find the actual data on my website for many batteries.

 

[arek98]

I was actually thinking about changing the battery setup. Since the frame i'm using is a tube bent in a circle, it's more convinient to use more, but slimmer, batteries. (something like this: http://www.batteryspace.com/sanyo-l...7-5-aa-size-3-47wh-0-28---un-38-3-passed.aspx) This way i can fit more batteries in this tube, and since it's quite small (1.9cm in diameter) i'll have less problems with the curvature.

Looking at the driver i saw that the minimum voltage is 5V, i think that i'll need to find another driver that supports 3.7 volts, and maybe that has an integrated PWM dimmer.

In this image you can se (more or less) the final setup. The yellow dots are the leds. The light should be diffused from there, and since the leds will be flush to the casing (because the idea is taht you will not see them) i think that the diffuser it's not really indicated. I'm planning to use 20 leds in order to diffuse light in a semi-organized manner, with the final goal ov not seeing the origin (in this case the leds) of the light. As always, sorry for the lack of wording

How big is this circle you planning? What is a diameter of tube used to build it?
Are you planning to have LEDs on inner side of circle and light in direction of center?
Or tube is translucent and LEDs will be inside with light going in all directions?


Driver I linked has 5V minimum because I thought you are going to use 2 or 3 Li-Ions.
Was thinking about something like that:

Drivers are linear so battery voltage needs to be slightly higher than LED string. They are simple to use (solder two ends) and cheap. You can pick current that is closest to your required runtime vs battery capacity. This will require more wires inside tube then one driver and single string of LEDs, depends on tube material this may not be an issue (will it be easy to hide or not).
With linear driver and one LED per one Li-Ion you should get efficiency about 75% with full battery and it will go up to almost 100% as battery voltage drops and gets closer to LED Vf (and eventually reaches it and current drops, LED dims slowly).
With one driver per whole string (note it is not recommended to drive parallel LEDs or strings of LEDs from single driver) assuming 3 Li-Ion and 18 LEDs we are talking about boosting ~10V to ~60V. You will need a very good driver to get above 80% efficiency and it will drop as battery discharges (bigger boost).

If you use 3 3200mAh 18650 Li-Ion batteries then you can drive 18 white 3mm LEDs with about 5mA to get close to 100h runtime.
3*3.7V*3.2Ah = 35.5Wh from this to get 100h you must be pulling no more than 355mW. 18 LEDs with Vf~3.5V is 63V and 355/63 is 5.6mA.