I want to make a light 'pen' to create calligraphy using light painting photography.
Examples of light painting:
Example1
Example2

Example of a tool I have made using a Led flashlight but one which does not give me enough light.


I was wondering If I can make a pen tool using 1W-6W led cob powered by AA batteries?
Led Cobs pictured below:

I will give the specifications of one of these cobs, the 1W 60 x 8mm.
If somebody can explain taking just this example, I think I can work out the possibilities with others.

COB1 - 60mm X 8mm
1. Chips: Epistar
2. Meterial: Aluminum-alloy plate + COB LED
3. Power: 1W / 3W
4. Input Voltage: DC 2-2.6(Red) 3V-4V (others),Max current :300mA(1W) / 1000mA(3W)
5. Luminous flux: 100LM/W
6. Light Color: Cold White (6000-6500K) , Warm White (2700K-3200K) ,RED(620-630nm),Blue(450-460nm)
7. Size: 60mm*8mm
8. Lighting area: 50mm*7mm
9. Low attenuation, 1000h attenuation<1%

COB2 - 100mm X 8mm
1. Chips: Epistar
2. Meterial: Aluminum-alloy plate + Silicon Rubber + COB chip
3. Power:5W
4. Input Voltage: DC 12V-14V Max current: 400mA
5. Luminous flux: >100LM/W
6. Light Color: Cold White, Warm White, Nature white
7. Size:100mm*8mm
8. Lighting area: 90mm*8mm
9. Low attenuation, 1000h attenuation<1%

I have very little knowledge of these things and I tried finding as much as I could.
I will try and put forward the little I have understood.

Alkaline AA batteries are rated 1.5 volts, while rechargeable NiMH AA batteries I was planning to use are rated at 1.2 volts
Alkaline AA batteries are rated 2500mah, while NiMH AA batteries are rated at 1900mah.

So to power a 12V light, I will have to put 8 Alkaline AA batteries in series in a holder... and similar calculations for others.
And if a cob is taking up 300mA, then using a 2500mah battery, I can get a 2500/300 = 8 hours.

Are these ideas correct?
When will I have to use a resistor?
What other factors do I have to take into consideration?
Are there any better options to make a similar tool?

 

You are on the right track, though you may be better off with a larger battery on your belt and a cable to the wand, the AA may let the LEDs get dim long before you think it should. Also a larger battery can be a rechargeable one.

It is hard to tell if you need resistors for the COB2, you probablyy do for the COB1 but without a link to the manufacturers data sheet we can just guess... so please provide a direct link.

Interesting project and a cool effect. Good luck and be sure to show us your final works!

 

When will I have to use a resistor?

if it is a portable application, you generally want to conserve as much energy as possible, thus having high efficiency is key. Resistors are the worst energy to high efficiency.

 

You are on the right track, though you may be better off with a larger battery on your belt and a cable to the wand, the AA may let the LEDs get dim long before you think it should. Also a larger battery can be a rechargeable one.

It is hard to tell if you need resistors for the COB2, you probablyy do for the COB1 but without a link to the manufacturers data sheet we can just guess... so please provide a direct link.

Interesting project and a cool effect. Good luck and be sure to show us your final works!

a. What battery would you suggest?
b. Why will the Leds start dimming quick on AA batteries?

These led cobs are off china. The link to the website where they are available for purchase.--> Here

c. What parameters do we have to watch for, to know if we are to use the resistors or not?

I will do the calculations for one, and let me know if its right.
Power:5W
Input Voltage: DC 12V-14V
Max current: 400mA

If I use 8 AA batteries, I will get 12V
Power is 5W
So current will be 5/12 = 416mA
Isn't it more than the 400mA specified, or this difference is negligible?


To know how many hours I'll be able to get out of them,
Should I do 2500/400 = 6.25
Or 2500 x 8 batteries/400 = 50 Hours!
And why?

Thank you

 

I reviewed the spec in the link and these appear to be simple LED devices on a board, with no series resistor built in. ("Simple" means the circuit is simple, the mechanics seem well thought out.)

Your calculates for 5W 12-14 V 400mA are correct, but your interpretation is not. What I believe they mean is 5W and 400 mA are the limits, and the voltage may be anywhere between 12 and 14 volts.

LED lights usually need a resistor because they are best thought of as current controlled devices, with the voltage not so well controlled. For example, if you had a batch of similar LEDs and put the very same voltage across each there would be a difference in the current they draw, or if you put the same current thru each then the voltage across would vary. That is just a normal products tolerance, it does not mean some are better or worse than the others.

So if a particular device is running at 12v when 400mA is driving it it is dissipating 4.8 watts. But if it drops 14 volts when getting 400mA the power is excessive at 5.6 watts, and you should not drive it so hard.

Using a simple resistor to limit the current always wastes power, and is not very exact, since the LED voltage may vary for many reasons. It is workable, but you have to add more batteries to use it.

A constant current drive would be best, though it too needs some voltage to work. I believe your skill level is below designing or building this, please confirm.


What you absolutely do not want to use is any sort of 0f PWM or pulsed control, since this will be visible in the pictures you take.

 

Thanks a lot for the knowledge.

My skill levels are almost zero. Though connections and soldering etc can be done with the help of a local electrician acquaintance.
If the constant current driver is just to be added in the circuit, I can manage that if I know which one to get.

What will happen if I just connect 8 AA batteries to that COB? (The one with 5W, 400mA limits)

 

Connecting batteries directly to the LED panel may work just fine, or you may get one bright flash followed by all the magic smoke streaming out. Please don't try it.

Let me make an analogy: say you stand at the top of a ski jump hill. You just stay still, no problem. Now inch forward a little. Still you stay in place. But as you inch forward you will find a point where you are suddenly going faster and faster down the hill.

That is similar to how the current reacts to a voltage in a LED. You can increase the voltage a bit and not much happens, then you hit the knee point where the current greatly increases for just a little change in voltage. True your voltage is basically fixed at the battery voltage but even a small AA cell can dump a huge current for a short time. You don't know what voltage this will happen at as it is somewhere in that 12 to 14 volt range.

I don't like a resistor here because the LED voltage can vary by a lot relative to a small voltage you would want across a resistor. You would find yourself selecting a different resistor to run each and every different LED wand. Not a clean solution.

Some sort of current output switching supply would be best where it adjust for the output current and makes the voltage be whatever it needs to be. These just be available for LED lighting but I do not know of such offhand.

I would hope some young bright fellow who knows of such would wander by and suggest something. If I have time tonight (a really big if this week) I will see if I can find something on say EBay. It should just be in the under 10 USD range.

 

Sure, whenever you get time in the coming weeks.
Thanks a lot.

 

If anyone else has any other advice till then?
Thank you.

 

Hi GoodBoy. Thanks for bumping the post, made it come to the top of my short list as I have a few minutes to mess about today.

I found this on EBay. It is an inexpensive DC-DC current output switching supply. It's adjustable so you can set both the current and the voltage at the output. (Think of these as a maximum, can't set both at the same time as that means the load would change.)

Should run off your batteries till they are deader than dead.

 

I want to make a light 'pen' to create calligraphy using light painting photography.
Examples of light painting:
Example1
Example2

Example of a tool I have made using a Led flashlight but one which does not give me enough light.


I was wondering If I can make a pen tool using 1W-6W led cob powered by AA batteries?
Led Cobs pictured below:

I will give the specifications of one of these cobs, the 1W 60 x 8mm.
If somebody can explain taking just this example, I think I can work out the possibilities with others.

COB1 - 60mm X 8mm
1. Chips: Epistar
2. Meterial: Aluminum-alloy plate + COB LED
3. Power: 1W / 3W
4. Input Voltage: DC 2-2.6(Red) 3V-4V (others),Max current :300mA(1W) / 1000mA(3W)
5. Luminous flux: 100LM/W
6. Light Color: Cold White (6000-6500K) , Warm White (2700K-3200K) ,RED(620-630nm),Blue(450-460nm)
7. Size: 60mm*8mm
8. Lighting area: 50mm*7mm
9. Low attenuation, 1000h attenuation<1%

COB2 - 100mm X 8mm
1. Chips: Epistar
2. Meterial: Aluminum-alloy plate + Silicon Rubber + COB chip
3. Power:5W
4. Input Voltage: DC 12V-14V Max current: 400mA
5. Luminous flux: >100LM/W
6. Light Color: Cold White, Warm White, Nature white
7. Size:100mm*8mm
8. Lighting area: 90mm*8mm
9. Low attenuation, 1000h attenuation<1%

I have very little knowledge of these things and I tried finding as much as I could.
I will try and put forward the little I have understood.

Alkaline AA batteries are rated 1.5 volts, while rechargeable NiMH AA batteries I was planning to use are rated at 1.2 volts
Alkaline AA batteries are rated 2500mah, while NiMH AA batteries are rated at 1900mah.

So to power a 12V light, I will have to put 8 Alkaline AA batteries in series in a holder... and similar calculations for others.
And if a cob is taking up 300mA, then using a 2500mah battery, I can get a 2500/300 = 8 hours.

Are these ideas correct?
When will I have to use a resistor?
What other factors do I have to take into consideration?
Are there any better options to make a similar tool?

AA's won't last long. I have a flashlight with a 3 W LED and it goes through D-cells (8 of them) pretty quick. But, boy does it kick out the light. No resistor or current limiting of any kind.

 

Re: post #10, this is listed as a buck convertor. Boost & boost- buck convertors are available.

 

Most of the boost or boost-buck converters I could find require 7 to 8.5 V input. So I would still use 8 Ni-mh with a constant current converter to give about 3- 4 hours use / charge ?
Most listings on boost, boost- buck converters in the fine print were shown as buck only ?

 

From LEDdynamics, 4015 Boost Puck, 04015-D-I, 350 mA adjustable downward, 5 V min, 10 V would be best. With 8, 2500 mAh Ni-MH AA bat., should give about 5 h. / charge.

 

Ouch- US $ 29. from Digi Key.

 

Do you have a volt meter ? If so and you just want to get on with it, I would use 12 NiMH AA batteries in series. Add several ( maybe 6 ) 5 ohm 1 W Rs in series with batteries. With all batteries & resistor connected, measure the V across 2- 5 ohm Rs ( 10 ohms ) . Move clip lead down one by one until V reads 3.5, or 350 mA. As batteries discharge move down another R. Should give about 5 hours. This is for the 12-14 V, 400 mA max.

 

It is much better to use 18650 Li-ion cells @ 3.4v to 3.7v and 4900mAHr to 6,000mAHr.
They are at least one sixth the volume. They are the only cells I use. $1.50 each. and $1.50 for the cell holder and $2.50 for the automatic, intelligent, charger.