Lighting Project powered by Battery

[Chrislee123]

This is my first post to EEVblog and will be my very first electronics project. Nevertheless I feel I am already losing myself in all the technical specs.

The project I am working on is too light four LED’s (4x10w) using a battery. The battery seems to be the biggest part of this project and I have done a fair bit of research into this area, the products on the market at the moment for batteries seem like they don’t match my specifications or budget, so I am proposing on creating my own battery packs.

The LED’s I am using are 4 x 10W LED’s, they are rated for 9-10V and 900-1050mA. I want each LED to have its own lens and reflector, but I am not sure which driver I should choose, how much power I will lose to the driver and also if each LED needs cooling, by a fan and heatsink, if so how much power am I expecting to use powering the fans.

 The Battery Pack I am going to create will be a 10p3s (30cell) 18650 pack, there are a lot of miss sold 18650’s on the market that have ridiculous capacities, but since I am going to be needing 120cells I can’t afford for Panasonics or Samsungs at nearly £10 for 2cells. So I will probably end up using a cheap-ish battery that has a good capacity. As a general guideline the batteries used will be 3.6V and hopefully about 2,900mAh/2.9Ah.

The 4 LED’s will take 9-10V @ 3.6/4.2A.
The 4 Battery Packs (30cell) will have a rating of 10.8V @ 116Ah.
The Estimated Time the 4 Batteries will power the 4 LED’s is 19.3hrs.

My question is does this project sound plausible/do-able? Is this sort of amount of energy needed unrealistic for project? Is there anyway I can squeeze more power? maybe running the LED’s lower? Any suggestions or discussions welcome.

[Paul Price]

Check the battery in your calculator?

If you have 4 x 10W LEDS than you require 4amps at 10V = 40 Watts, in any case the 4 LEDs will draw a total of 4-amps each hour.
If you have 4 batter packs each with 30 cells at 116 AH total at 10V then you will have a total of 464 AH capacity.

19 hours should be a cinch, and you will need some sort of PWM control to limit current for each of the LED's.

And LED's are still  much less than 100% efficient and so each will require a heatsink.

Whether or not you need a fan will depend on the size of the heatsinks, the ambient temperature, ventilation within your enclosure, etc.

With some sort of PWM control, say from a MCU board driving MOSFET as Lowside switches, you could adjust the brightness so low that  your batteries could last years before recharging at this lowest brightness or more than 19 hours you want at full power.

Howya gonna charge all these batteries is another question.

[CraigHB]

My question is does this project sound plausible/do-able? Is this sort of amount of energy needed unrealistic for project? Is there anyway I can squeeze more power? maybe running the LED’s lower? Any suggestions or discussions welcome.

Yes it's entirely plausible.  People fly model aircraft powered by Li-Ion batteries that consume several kilowatts so 40W is no problem.  With your drain requirements you can use the highest capacity 18650 cells.  Those provide the best energy density in terms of size and weight.  They also provide the least cost per Amp-hour in terms of 18650 cells.  Though if size and weight are not a constraint, the high drain 18650 cells are more efficient.   However they are more expensive since you need more cells for a given capacity and they occupy more space and carry more weight.  Li-Ion batteries used for powered models more specifically known as LiPos probably provide the lowest cost per Amp-hour, but energy density is quite a bit lower even compared to a high drain 18650.

Be careful buying no-name or unknown name 18650 cells.  There are many unscrupulous sellers providing cells that do not meet the specs they claim.  You really need to stick to a name brand or a brand known to be of good quality.  If you're looking for the cheapest cost per Amp-hour, check out the LiPos used for powered models.  Take a look at them over at http://hobbyking.com  The HobbyKing branded Turnigy batteries are good quality and deliver advertised performance.  I use them myself for the model helicopters I fly.  Check out the "MultiStar" line specifically, they have some very high capacity batteries.  The down side with those is they will take up more space and weigh more than 18650 cells, but it would be the least expensive solution.

[Zero999]

What sort of power supply do you intend to use? Resistor, constant current, switched mode?

I like to use LED modules which have the driver built-in. You can get some very good MR16 12V LED halogen replacement lamps, which will work from DC too.

[edavid]

For your first project, you really need to scale this down to something simpler.  A single 10W LED would be a much better project (still pretty challenging).

A 3S battery pack is a poor choice here.  You want the battery voltage to always be substantially higher or lower than the LED voltage, so you can use an ordinary buck or boost DC-DC converter.