Introduction: Build the Ultimate LED Lamp (Li-ion)

Emergency lamps are one of the most important household essentials, mainly because we use it on various applications. You can use it during blackouts, while camping, doing videoshoots, doing photography and other stuff... Over the years, we've bought a lot of Lead-Acid Emergency lamps. From incandescent, to CFLs, to LEDs.

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My main application for these lamps is for handywork and videography. None of which we had was powerful enough to light up the subject on a three - point lighting setup. Hot shoe video-lights are a bit pricey. As an enthusiast I decided to make a cheaper version. Cheaper but better! Better in all ways!

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Behold a DIY LED lamp with 9x 3watt LEDS, powered by four Lithium-Ion batteries and controlled by a dimmer circuit. It lasts for around 4 hours to 4 days (depending on the dimmer's setting).

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I'll be posting a video follow-up next week, similar to my FM Transmitter Project Video.

Step 1: Parts & Tools

Discrete:

- 3W White LED (9x)

- TIP35c NPN Transistor

- 7805 Voltage Regulator

- 1.5k 1/4w Resistor

- 10k Trimmer Resistor

- 220uF Capacitor

- 100nF Capacitor (2x)

- Plastic Standoffs (4x)

- On/ Off Switch

MISC:

- 18650 Lithium-Ion Batteries (4x)

- Rectangular Plastic Container

- Solderless Prototyping Board

- Perfboard (Breadboard)


Tools:

- Leatherman (Multitool)

- Digital Multi-meter

- Bench Supply

- Soldering Iron
- Cutting Board

- Hotglue Gun

Step 2: Screw the Standoffs

Screw the plastic standoffs to your PCB.

Step 3: Position the LEDs

Use a little amount of superglue to temporarily position the LEDs.

Step 4: Solder the LEDs

Now solder your LEDs to the PCB. This should hold the LEDs in place.

Step 5: Test It

Supply a 9v power supply to the LED array. Regarding the heat, the LEDs get very hot at 9v (max brightness). At 6-7 volts the LEDs barely dissipates heat, the PCB absorbs the very little heat given off. Bottom line, never use this setup at its max, only tune it at half the brightness. BTW, half is still bright, brighter than your average videolight.

Step 6: Prototyping the Variable Regulator/ Dimmer (Part 1)

We need to control the brightness of the LEDs with a dimmer circuit. There are two ideal circuits to use: the PWM buck converter and the Linear voltage regulator. The buck converter is more power efficient compared to the linear regulator although when you shoot videos using a light source controlled by a PWM buck converter, the videoclips tends to tear.

Here's the schematic diagram of the circuit: the 7805 regulator is used as a voltage reference for the high current transistor while the trimmer capacitor is used to control the voltage of the transistor's base.

Step 7: Prototyping the Variable Regulator/ Dimmer (Part 2)

Time to test it! Try to supply voltages from 10v to 30v. The regulator should give a constant voltage output. Try to rotate the trimmer the voultage should change from 4v - 9.5v.

Step 8: Solder the Dimmer to the PCB

Once you get the dimmer circuit to work, you can now install it to the same PCB where you soldered the LEDs.

Step 9: Add a Switch

Now, drill a hole, hotglue a push button toggle switch then solder it to the dimmer circuit.

Step 10: Assemble the Lithium Battery Pack

Recently I found a store that sells lithium 18650 Lithium-Ion batteries for $2 each. Each cell rated at 3.7v (2000mAh). I soldered four of them in series to build a 14.8v (2000mAh) battery pack. Be sure to solder them fast, otherwise things could go wrong once you heat them up too long.

Step 11: Solder the Battery Pack to the PCB

Now, solder the battery pack to the dimmer circuit.

Step 12: You're Done!

Enjoy your dimmable LED lamp! :D

Step 13: Give It a Try! :D

Step 14: Maintaining and Charging Your Batteries

Lithium batteries need special chargers, also known as balancing chargers since they are very sensitive to overvoltaging.

Step 15: Final Thoughts and Observations.

The PCB acts as a heatsink upgrading to a fiberglass PCB would improve heat conductivity and heat resistance. Adding a fan would probably solve the problem. The lamp get too hot at full power, would only last for 10 minutes without a fan. Although it could run as long as it could at half the power.

Step 16: Mistakes to Be Corrected on My Next Attempt

*Use a high-efficiency buck converter.

*Use Lithium-Polymer

*Add a large heatsink

*Add a fan

*Add an ATiny85 MCU (as a digital controller)

*Add a tiny LCD panel.

*Gel diffusers maybe?

Comments

author
mohda136 made it!(author)2017-04-15

Hi,

Just wanna ask, why did you think using Li-ion battery is a mistake? What is the advantage of using Li-Polymer battery for this project?

Thank you.

author
MuhannadMaklad made it!(author)2015-04-08

sorry, but what is the use of the transistor ?

author
Yonatan24 made it!(author)2015-12-25

I believe it was used for the dimmer module

author
Yonatan24 made it!(author)2015-12-25

In step #12, Pictures 2&3 don't have the same LED's in the middle, Is there a reason for that?

author
Yonatan24 made it!(author)2015-08-29

Hi,

I was wondering where you bought the screw standoffs

Thanks in advance :)

author
sreeci made it!(author)2015-02-19

I have 3 issues to discuss. Kindly verify, comment and explain.

1) Star LEDs produce tremendous amout of heat.

They can self destruct if left without heat dissipation.

There was no mention of heat sink.

2) Soldering Li-Ion batteries on to its body!

Liquid Lithium becomes unstable when hot, unless cooled. (Li-Ion batteries with Tabs are available)

3) Where did you buy Li-Ion battery 18650 for $2 ?

Let us know the location.

Thank you for your publication and thank you in advance for the response.

author
crickleymal made it!(author)2015-01-01

A good first attempt. As you and others have said, a heatsink is really needed. Also you can buy cheaply some great little lenses to fit over the leds to focus the light a bit more.

Neat dimmer circuit though.

author
gsantony made it!(author)2015-01-02

where to connect the heatsink in this circuit

author
JinkyDrew1 made it!(author)2015-02-15

stick a old cpu cooler on there... will cool miles better than anything else will

author
Electrospark made it!(author)2015-01-02

An LED heatsink is a piece of aluminum that you place the LED on to dissipate the heat like the LED chip set heatsink on the picture. for even more heat protection, you could place all the LED's on LED heatsinks and then place them all on a big heatsink that has fins but that would be a bit overdoing it.

Hope this helps.

led.jpg
author
gsantony made it!(author)2015-01-03

thanks a lot then one more question ....in this circuit did not mention battery specification ...can you help me

author
Electrospark made it!(author)2015-01-03

I think the circuit uses about 500mA (Milli-Amp) so if you use 500mAh (Milli-Amp hours) batteries it will last for about an hour, If you use 1000mAh batteries it will last for about 2 hours and so on.

That means that if you have a circuit that draws 1000mA, and you use a 1000mAh the battery will only be able to run for an hour since it's maximum capacity is 1000mA for an hour.

Now, if you have a circuit that draws 500mA and you use a 1000mAh battery it will run for two hours since after an hour the battery would only have used the half of it's charge.

That means that the more mAh a battery has, the longer it will last.

And the lower the amp draw of your circuit is, the longer it will run.

Here some example of the run time you will get from the LED light depending on what batteries you use.

Under 500mAh= batteries overheating and draining very quickly.

-500mAh=1 Hour

-1000mAh=2 Hours

-1500mAh=3 Hours

-2000mAh=4 Hours

-2500mAh=5 Hours

Note that this is just for a circuit that draws 500mA like the LED lamp and that the run time will be different depending on the amp draw of your circuit.

there is also the batteries chemistry but that's another story...

If you want to know some info about that, Just let me know.

I hope all that info will help you.

author
gsantony made it!(author)2015-01-04

thanks for these details already i know these things what i need to know is voltage of the battery like 1.5v or 3.3v or 6v or 9v ...... can u tell me list of components with specification clearly and exactly for this circuit because i am going to try this circuit alone

i need like this

3W White LED -9 nos

- TIP35c NPN Transistor-1no

- 7805 Voltage Regulator-1no

- 1.5k 1/4w Resistor -1no

- 10k Trimmer Resistor-1no

- 220uF Capacitor-1no

- 100nF Capacitor -2nos

- Plastic Standoffs (4x)

- On/ Off Switch

-battery (voltage? mAh)

expected these alone......

author
Electrospark made it!(author)2015-01-14

Huh, They are 3.7V not 2.4V. He just updated his instructable and said they were 3.7V.

Sorry about that.

author
gsantony made it!(author)2015-01-31

No problem.......may i use this 9 number of 3W led, directly into 9v DC supply

????because i dont want battery .....

author
Electrospark made it!(author)2015-01-31

You can, but you'll have to connect them in set of three in series connected in parallel.

I recommend using a 12V power source with a voltage regulator at your input to have a steady 9.6V output for best results.

You may also want to connect a current limiting resistor on each set of three and attach the chip set LED heat sinks to a big heat sink to have a longer lifetime.

author
Electrospark made it!(author)2015-01-04

Ah, I see what you want to know, he used four Li-ion batteries of 2.4V and a capacity of 2000mAh in series to obtain 9.6V at the output.

Sorry for the misunderstanding, if you ever have any question about electronic circuits, feel free to contact me! :-)

author
karlpinturr made it!(author)2015-01-13

Unless I'm missing something, 18650's are (as ASCAS states later, when soldering them) rated at 3.7 volts, giving a pack voltage of 14.8.

author
Electrospark made it!(author)2015-01-14

He updated his instructable and said the voltage of them was 3.7V.

I thought they were 2.4V because of the picture of the multimeter on the picture on step 7.

Look's like i was wrong...

author
karlpinturr made it!(author)2015-01-15

Ah! - Mind you, his circuit diagrams suggest he's not putting more than 9v through the array, so his dimmer circuit must be dropping the voltage considerably at some point - makes me wonder why he's used 4 batteries when 3 would give 11.1v, which I presume would be easier(?) to drop to usable voltages. Then again, we're really in realms I don't understand...:(

author
Electrospark made it!(author)2015-01-15

I think it's to get a longer run time.

The higher the voltage, the longer it will take for the batteries to get to the voltage where it starts to affect the brightness which is 9V in that case.

author
karlpinturr made it!(author)2015-01-15

Hmm - I see what you mean. Thanks!

author
Electrospark made it!(author)2015-01-15

No problem, it was a pleasure to help! ^_^

author
wobbler made it!(author)2015-01-04

If the circuit is using only 500mA, then the reason the LEDs aren't burning out without a heatsink is because they are being quite significantly underpowered. 500mA @ 9.6v is 4.8watts in total instead of the potential maximum of 27W, or approx. 175mA through each LED instead of a typical maximum of 1A for a 3W LED at full brightness. Therefore, each of the 9x3W LED is dissipating approximately 0.5W each (0.4W in heat if you allow for 20% efficiency in converting energy to light).

This means you can either make your array a lot brighter, but would definitely need a heatsink and probably better current limiting on each chain or could design it with the same light output using only 2x3W LEDs but driven with a greater max current each, but again you would definitely need appropriate heatsinking.

However, to drive the array fully at 3W per LED would require approx. 3A and the 1Ah batteries would last about 20mins, but it would be bright! A 3W LED bulb is rated as equivalent to a 25W incandescent, so your array should potentially be equivalent to 9x25W or 225W of incandescent light.

author
Electrospark made it!(author)2015-01-04

The amp draw at full brightness is more like 3000mA.

author
wobbler made it!(author)2015-01-06

@Electrospark:

I was basing my reply on your previous comment "I think the circuit
uses about 500mA". It's only repeating a lot of what others have said
about the need for heatsinking.

The other problem with this
circuit is due to putting the LED chains in parallel. LEDs are current
driven devices so this means that really each chain should have some way
of balancing out the current. This is usually done with small current
limiting resistors in each chain. If not, there is the danger that one
chain will take significantly more current than the other two, resulting
in either an imbalance in light output across the three chains or one
chain getting much warmer than the others and then failing.

Regarding
the heatsink, it's easy enough to work out what size heatsink to use.
There will be a rating of maximum temperature on the LEDs, which you can
easily get from a datasheet. This is about 75 deg C from one I looked
at. These LEDs at full power are trying to dissipate roughly 27W so we
need a heatsink which will keep the temperature below 75 deg C. If we
assume an ambient temp of 35 deg C max then it will need to limit the
temperature rise to 75-35=40deg C. You then divide this by the watts you
are dissipating to get the degrees C per W rating of the heatsink, in
this case 40/27=1.5 deg C/W.

A 1.5 deg C per W heatsink is big (and expensive)!!- one is here and is 100mm x 66mm with 40mm fins. A 0.75 deg C per W is even bigger:

http://uk.farnell.com/fischer-elektronik/sk-100-10...

http://uk.farnell.com/fischer-elektronik/sk-85-150...

However,
this means you would be running the LEDs at max temp, which is not
good. In addition 75 deg C is hot enough to seriously burn you so I
would use a bigger heatsink, maybe rated at only half that (0.75 deg
C/W). As an idea of what 75 deg C means, water from a tap is best kept
to 50 deg C to avoid scalding and 60 deg C will produce a third degree
burn in 5 seconds.

In addition, 3W LEDs can make expensive fuses if not cooled properly.

ref:http://www.antiscald.com/prevention/general_info/table.php

author
Electrospark made it!(author)2015-01-06

I don't know if you're right about the current limiting resistors, they would have to be 1W+ rated and never saw any in LED light bulb driver circuit, they are usually directly connected to the 32V, 300mA output in series, but i don't know if they are needed if they are in derivation setup.

I already made some LED beads lamps in derivation setup and i didn't used current limiting resistor as i thought they were not needed for Power LEDs as long you wouldn't exceed 3.3V at them.

The exact power consumption of this lamp is 2812.5mA at 9.6V.

Total of 27W.

He used 2000mAh batteries, that's just enough power for 43 Minutes of run time and they will get hot after a while.

Of course they last 4 Hours because they are new, but after a few recharge cycle they will start to drain faster.

For the heat sink, As you said you'll need to use a big one if you want them to last 100,000 Hours.

But LED Base plate heat sinks are okay and will only get hot but not burning hot, Of course you will get a shorter life from your LEDs but your light will be more compact and way less heavier.

If you don't use any heat sinks you'll end up with burnt LEDs after only a month or so.


author
starphire made it!(author)2015-01-13

Current limiting resistors are actually quite common in LED light engines and packaged LED lights of all kinds. It really depends on the configuration of LEDs and the circuit driving them. A 1W chip resistor is only about 1/4 inch long, but sometimes the load is split into smaller resistors by putting more than one in series.

Oh, that 100,000 hour number is pretty unrealistic, esp. for white LEDs because the rating is based on how long it takes for the light to dim to a certain percentage of its original brightness (typically 70%), not how long until it fails completely. For white LEDs, this is more like 20-30k hours because the phosphor degrades faster than the LED chip itself. But in any case, you are right that it takes a properly sized heatsink to get that kind of lifetime and it will need to be MUCH bigger than those itty bitty hexagonal boards that are often paired with power LEDs.

author
Electrospark made it!(author)2015-01-14

Okay, thanks for the info, It'll be helpful in the future I'm sure.

"I live, I learn, I get better at it" :-D

author
Electrospark made it!(author)2015-01-04

I thought he used 1.2V batteries, I then checked and saw i was wrong. :P

It would be 1.6V per LED, haha!

Sure it would be underpowered!

author
starphire made it!(author)2015-01-13

Oh dear! Apparently people are getting the idea that these star boards were meant to be sufficient in and of themselves as heatsinks for the LEDs mounted to them. But that is a totally erroneous idea! In fact, they were originally created to *simplify* the mounting of power LEDs to a proper heatsink. Yes, running a 3W LED on a star board is worlds better than using essentially no heatsink, but that is absolutely not going to keep the actual LED die (the critical part of the whole system) below the mfrs. recommended temperatures for long life. You might not notice degradation or early failure on LEDs with no additional heatsinking, but that does not mean it is not accelerating the process or risking early failure!

To go a bit further, if we were to assume 27Watts total power dissipation from this lamp, it would *definitely* require a thick slab of aluminum with fins coming out the back to keep the LED die temperatures in the safe zone. It's a simple formula to calculate the predicted LED die temperature from the published specs for thermal resistance from chip to LED package, thermal resistance from LED package to star board, thermal resistance from star board to heatsink, and measured temperature of the heatsink after it's been running for some minutes. Sure, you can wing it and get something that appears to work without burning your hand on the heatsink, but no professional LED light designer ( I say this as one who has been doing this for 10+ years) would skip that validation step if they intend to make a light that actually lasts for tens of thousands of hours without significant rate of brightness loss or early failures!

author
Electrospark made it!(author)2015-01-14

Heat sink it is! ;-)

author
eric005 made it!(author)2015-01-17

is there a power supply that you can plug into a 110v wall socket instead of using batteries.i was thinking of making a desk lamp

author
rhroy made it!(author)2015-01-15

where did you find these LEDs?

author
Electrospark made it!(author)2015-01-15

Ebay is a great place to buy them.

Here's a link to buy 50x 1W LED beads for under $5...

http://www.ebay.ca/itm/361002082770?var=6303400893...

author
voblak made it!(author)2015-01-14

What about undervoltage protection?

author
Electrospark made it!(author)2015-01-14

Haha! That's funny.

Huh, Was it a joke? :P

author
FlorianS made it!(author)2015-01-14

PWM works you just have to use a higher frequency (>10khz maybe) Nice Build!

author
Ren%C3%A9B2 made it!(author)2015-01-13

That circuit is absolutely over-complicated and weird. You can use an lm317 as a current source, with one resistor per parallel led branch you would be fine then. Alternatively you could use an L200 which is made to be a current source and needs control resistors of smaller wattage.

author
ASCAS made it!(author)2015-01-14

I made this project in a rush. I was out of parts at that time, so I was forced to construct a circuit using parts I had at that time.

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The LM317 could only provide 1.5A of current, my LED array consumes 3A max.

author
Ren%C3%A9B2 made it!(author)2015-01-14

Okay, I just wanted to point out that this circuit is not the ideal one.

While you are right that an lm317 is not powerful enough here, it is at least made for voltage regulation, while the lm7805 is not; Furthermore, one could use a current mirror here to properly drive the transistor. Maybe I can mock up some circuitry; have you made your circuit on a website?

author
nqtronix made it!(author)2015-01-04

Sometimes there are bad days. You know, those days when just everything fails. Two days ago I typed in a long ass comment, but just before I was finished I ran out of battery. Of course, I had nothing saved. When I put away my laptop I did not unplug the ethernet cable and somehow managed to ruin the network port. Great. It took till now to get the WLAN up and running, but hey, now everything seems to work.

So please forgive me that I'm not retyping everying but I still want to give you a quick summary.

As ASCAS has allready mentioned the thermal design is clearly not the best. It will get hot, too hot, so we to solve this problem.

1. So how much heat does the current design produce at maximum brightness?

Let's assume the LEDs reach their maximum power at the 9.5V max. Output of the regulator. To reach (9*3W=) 27W it requires 2.84A. At a battery voltage of (4*3.7V=) 14.8V this means about 42W are consumed in total. To be fair, not all energy is converted into heat, about 30% of the LED's power is emitted as light. Thus a total of (42W-27W*0.3~) 34W is left.

2. If we could reduce the heat generated we have to get rid of less, so lets start here. For obvious reasons we can't reduce the heat the head generated by the LEDs, but we can choose a better (more efficinent) LED driver. The driver used right now turns with full batteries and maximum output of 9.5V about 5.3V into heat (technically not 100% correct, but precise enough for the given purpose) resulting in an efiiciency of just 64%. Step-down converter on the other hand have an efficiency of 90-95% which would result in a power loss of 2 to 4 W instead of the previous 15W!

Still, even with a better driver there ist still roughly 22W to disapate, which is a lot. To put that into perspective: go agound your house, find a 25W light bulb, turn it on, leave it like that for a few minutes and then touch it with bare hands. You'll figure out it will be *slightly* warm:

3. Ok, but how do we get rid of all that heat? First we need to know how hot LEDs are allowed to get. I did a quick google search and the first 3W LED in the same case could be used up to 100°C, so I'll stick to that for now. Second we need to specify the maximum operation temperature of our device. 40°C is a good starting point assuming we want to be able to use the device in the summer. Thus the the maximum temperature rise should be below 60°C (= 60°K). All left to do is to search a heatsink with a power dissapation value of (60°K/22W=) 2,7°K/W or less. Sure, you still need to mount the LEDs properly with thermal paste or thermal glue. Once smoke of burned superglue hits your eye you'll think twice next time, if superglue is the right choice. Don't forget small holes in the case to enable airflow.

4. It is important to note that step-down technology isn't the same as PWM. Step down uses much higher frequencies (100khz to a few Mhz) so it won't be visible on normal video, independet of the shutter speed. Just as important is that you should get a step down converter with a constant current output, I don't know off hand a chip that does that, but sure there are some. If it has some sort of external current control which can be modified during operation you have a professional grade, flicker-less LED dimmer.

5. Since you plan to include a microcontroller anyway make sure to include a temperature sensor as well. If the temperature of the heatsink reaches critical regions (say 90°C or so) the microcontroller could reduce the light output to reduce power consumption and thus the temperature as well.

After all this comment got longer that I wanted it to (and neither quick nor a summary), but I hopes this helps anybody (and was worth the effort).

If any questions are still left, feel free to ask and I'll try to answer asap.

- nqtronix

author
rtorres20 made it!(author)2015-01-13

Thanks for that explanation, it surely will help me out a lot in the near future. I'm glad I read through the comments, thanks!

author
nqtronix made it!(author)2015-01-13

I'm glad I could help :D

author
nimrar made it!(author)2015-01-13

Hi very best

Best regards,

author
three_jeeps made it!(author)2015-01-13

To echo some of the comments:

Step-down regulators with constant current is the way to go. Most efficient ( I learned this doing a project that involved lighting 1000 LEDs in the bad old days).

Use a micro to monitor temp and monitor the run time to that the unit will turn off automatically at points along a brightness-visability curve is followed.

Include a separate battery charging/management chip to condition/charge the batteries in the most efficient manner corresponding to their chemistry.

And finally, *spend $1 and get a plastic battery clip* or get batteries with tack welded tabs...OMG, soldering batteries is living very dangerously...

author
Electrospark made it!(author)2015-01-13

Sure! :-)

author
mkinoma made it!(author)2015-01-13

Interesting project, thanks for the schematics. (Soldering batteries! Brave…)

I'd love to see a followup about long-term performance. High-power LEDs require some thermal management, usually featuring a thermal connection between a heatsink on the PCB and a pad on the back of the LED.

Dimming via voltage tends to change the color of LEDs, so it could screw up your white balance or cause conflicting color temperatures on the set.

I think it would be really interesting to use PWM but time it off of external ref sync – genlock your lighting! – to avoid tearing. There are synchronous PWM driver chips out there, like the ON Semiconductor NCP3011… Clock it using a PLL frequency synthesizer off of video clock in from a digitizer chip like the Marvell 88DE6010. With sufficient frequency, tearing could be avoided, and with genlock and even multiples you could also avoid rolling.

author
tyscof made it!(author)2015-01-13

What store?

author
pointedspider made it!(author)2015-01-13

The LEDs need a heatsink!!!
That's number one!!!!

Two... when soldering li-ion batteries, wrap a wet cloth around the cell near where the heat will be. I use 40 watt iron and it only takes 2 seconds. Also on the positive end of the battery, avoid the edges where the blue (or whatever color you have) because negative is under it. could be easily shorted resulting in a fire.

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Bio: Hi I'm Angelo! I am a 18 y/o college sophomore taking my majors in BS-ECE at the DLSU. I use my course as ... More »
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