# Portable lamp using LED and 12V battery



## DanielJ (Sep 10, 2013)

Hi everyone,

I am working on a project to create a portable LED lamp that is powered by a rechargeable 12V 8400-9500 AH LI-ion battery pack.

Now my math tells my that using a 3W LED bulb, the item will be able to be powered for 33.6hr-38 hrs. 

I was told by friends that, upon recharging, the battery life will not be nearly what it was originally. Is there truth to this?

Also I am using a 3W LED to try to light a 10", 12" and 14" lamp, do you feel this will be adequate? My goal is to find a balance between battery life and brightness and feel that this might be that sweet spot.

Please offer any suggestions (LED bulb suppliers, battery comments) that you might have.

Thanks!


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## Toaster79 (Sep 10, 2013)

LiIon batteries won't degrade after first recharge if charged right. Charge rate of 0.5C will keep them at 100% when quality cells are used for about 500 cycles when not overdischarged/overcharged.


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## Steve K (Sep 10, 2013)

DanielJ said:


> Hi everyone,
> 
> I am working on a project to create a portable LED lamp that is powered by a rechargeable 12V 8400-9500 AH LI-ion battery pack.
> 
> ....



just to check... the battery capacity should be 8400-9500mAH, right?

And you'll be using a switching power supply to drive the LED from the 12v battery? 

No comments about brightness... I don't know what a 10" lamp is, nor 12" and 14", and don't know what the space is that you want to light up with this 3W LED.

Still... it's an interesting problem. I just picked up a 12v battery jump start pack, and am contemplating putting together a quick LED work light that could be used when changing a flat tire in the dark, or perhaps using it to light a room during a power outage.

I do think that your numbers reflect using the whole capacity of the battery, and that might not be best for the battery. Deep discharges are worse for some battery chemistry and configurations than others.


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## SemiMan (Sep 11, 2013)

Toaster79 said:


> LiIon batteries won't degrade after first recharge if charged right. Charge rate of 0.5C will keep them at 100% when quality cells are used for about 500 cycles when not overdischarged/overcharged.



Cobalt Li-Ion will not stay at 100% for 500 cycles. Perhaps 80% especially for a near 100% discharge. Add in the deterioration in capacity from just sitting there fully charge and you are likely going to be below 80% after 500 full cycles.

For long life, better to go LiFeP04. Then you may get a few thousand cycles to 80% capacity even with near 100% charge/discharge cycles.

Semiman


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## ianfield (Sep 13, 2013)

Steve K said:


> just to check... the battery capacity should be 8400-9500mAH, right?
> 
> And you'll be using a switching power supply to drive the LED from the 12v battery?
> 
> ...



Overdischarging pretty much kills most Li chemistry cells so a UVLO with load disconnect transistor is highly recommended. Overcharging Li chemistry can cause a lithium fire (even some time after taking off charge) that will flare up even worse if you chuck water on it (your best bet is bury it in sand) There's a *VERY* good case for using a manufactured charger with certification and for the correct type and number of cells.


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## LEDealer (Sep 13, 2013)

What is the Vf of your LED?

Are there any 12V LEDs out there from the big boys right now?

Does it even make sense to go with a 12V version of the Nichia 219B (if it were to exist) vs a 3V version?


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## Christexan (Sep 20, 2013)

In reverse order... there are 12V (ballpark) LEDs, Cree actually makes a variety of LEDs in a variety of voltage ranges, from standard single-dice 3.xV to hundreds of volts streetlight packages. Bottom line though, ALL (white) LEDs are based on the same 3.x volts chemical formula, the only differences are how many are in series to make the resultant voltage (through encapsulation of multiples into "one" cohesive package, or through just putting lots of singles together in a string). 

Regarding the OP and "lamp size", that's up to you, 3W is 3W, and you will get "x lumens per watt" output based on the heating of the LED. The only differences you'll see in usage are based on the optical configuration (package, and add-on optical setup). You can light any of the lamp sizes you specify, are you looking for an area lamp, a spotlight, etc? A 3W LED through a fresnel or aspheric lens, can light up a wall of a house 300 yards away well enough to read a book at night by, and that same LED with no additional lens and a standard 120-degree optic, won't be usable for reading a book 20ft away. 
Regarding lithium chemistry, most lithium (and nickel as well) chemistries actually improve slightly in the first 5-10 charge/use cycles. Basically charge distributes a little more evenly than it's initial charge distribution, slightly increasing performance. After that, assuming you use it in a proper fashion (reasonable charges and discharges), your lithium will very slowly degrade over time (not noticeable for months, or a couple hundred uses really). 
All lithium DOES degrade, it doesn't matter if you use it, charge it, or not, the battery sitting on the shelf will lose capacity over time (all chemistries, not just lithium, do this). As mentioned, the "highest capacity" lithiums (cobalt formula, the common laptop battery lithiums) degrade to about 80% of initial capacity over 2 years, whether or not you use them. That process increases beyond that, which is why it seems all laptop batteries need replacing after 3-5 years, whether you use them a lot or not. You CAN kill them faster through deep-discharges, but normal charging, run down some, recharging, they won't degrade much faster than not using them. 
LiFePO4 cells are tougher, they degrade on their own much slower (longer shelf life), have a longer cycle life (about 2-3x cobalt, especially if used occassionally, over a course of years), and they are more tolerant of heavier usage (which is why they are common in power tools). However they run a lower initial voltage (3.2 instead of 3.6 nominal) and their overall power density (Ah/gram) is about 20% lower than cobalt lithiums. However their durability, lack of explosiveness (their chemistry is much less reactive than cobalts), and tolerance of a wider range of conditions, makes them a better choice for nearly any "DIY" project. 
Regarding battery... your switching regulator is going to determine efficiency, and your output voltage (which LED/array you choose) will determine the amperage used. But based ONLY on "12V source, 3W LED" gives us 3/12 = 0.25amps. Divide your 12V power source rating in amp-hours (8400) and get 33,600 hours. HOWEVER my guess is you meant "mAh" (milli-amp-hours), or 8.4Ah. so make that 33.6 hours, as you correctly calculated. There will be switching losses, on any "theoretical" number, I use 80% as the final number, so 33.6*.8=26.88 hours. 
As mentioned, that's from fully charged to fully run down, not recommended. If you only need a light at night though, and use it 8-10 hours, then recharge, you should cause no real stress to the batteries. IF you run it 4 nights in a row, then recharge, you are going to shorten your battery lifespan.


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## ilovewatermelon (Oct 19, 2013)

DanielJ said:


> Hi everyone,
> 
> I am working on a project to create a portable LED lamp that is powered by a rechargeable 12V 8400-9500 AH LI-ion battery pack.
> 
> ...




to ensure the longest lifetime for any battery , you should discharge half , then recharge , do not discharge over half of its aH 

can you double up the battery ? and re-charge when half empty ?


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## Barbarin (Oct 23, 2013)

Hi,

Nowadays good quality MR16 lamps are getting more tha 70 Lm/watt, with +80 CRI, and pulling from the battery 4,5 Watts. You have too longer body versions achieving 550 lm at 6,5 Watt IMHO there is very little point in messing arround with custom circuits and so on. What is more, if your prepare your device to be able to use MR16 lamps you can upgrade it easily and have diferent options for different tasks (angle, output, temperature...)

javier


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## SemiMan (Oct 23, 2013)

ilovewatermelon said:


> to ensure the longest lifetime for any battery , you should discharge half , then recharge , do not discharge over half of its aH
> 
> can you double up the battery ? and re-charge when half empty ?



There is no magical 50% value. That is a somewhat meaningless rule of thumb that applies a little to lead acid and almost not at all to other technology.


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