Cree Headlamp Dealextreme sku.12275

[pxbaroni]

Great light for the Money!

So far this is a great light that I found for little money. I am not a electonics person and wonder if anyone here could answer these questions.
Regarding this light!
Question to the knowledgable...I am making a battery pack and extending it to a camelbak for mountain biking. I am thinking of building it with 5 x 1.2v nimh batteries bringing the voltage to the same as 4 x 1.5v alkaline. The voltage should be identical, and it should increase my run time. Any ideas would be great. Questions are:
Will it burn brighter?
Will it run longer?
Will it hurt the light?
Thanks in advance,
PXB

 

[Marduke]

5xNiMH will have a much higher voltage than 4xAlkaline, and will likely fry the system. Using 4 NiMH cells directly in the supplied holder will get you a longer running, brighter light.

 

[pxbaroni]

Thanks for the reply…any chance you have a minute to explain the voltage issue. As I said, I am not knowledgeable...however, mathematically it seems that 4 x 1.2volts = 4.8 volts and 5 x 1.2volts = 6 volts. This light is a 6 volt system. 4 alkaline batteries = 6 volts, not 4.8, and that is what is in the light now although it runs with nimh batteries too. Do nimh batteries drive power differently? Help is appreciated...I am trying to get up to speed on this stuff.

 

[Marduke]

Alkaline peak at 1.5v, and quickly drop in voltage under load. NiMH start out at about 1.4v, and maintain a higher voltage than alkaline cells under load. This is do to NiMH having a lower internal resistance.


In the LED world, more voltage doesn't mean brighter. White LED's need about 3.5-3.7v. A light has to either raise or lower the voltage to that level for the LED to operate. So, for a 4 cell light, as long as the voltage remains above about 3.7v, the light will be about the same brightness until the batteries are dead.

 

[Mitica]

I've just received this lamp yesterday and I'm excited.. It's my first lamp that uses a led from the new generation.
Regarding batteries, I think that you better go for a D size battery pack since you are building your own. One extra AA will not bring too much gain in running time and I guess the lamp will not be brigher since it's regulated.

LE: Did anyone had the chance to measure the output of the driver for P4? My guess is that the led is driven at less then 350mA

 

[hopkins]

hi pxb - better stay with only 4 cells. You'll get some extra runtime if you take the nimh cells out of the charger just before a night ride.

Is this headlamp all plastic? Any heatsink metal sticking out to carry away the heat from the Cree? If possible take the head apart after running on high for
10 minutes with fresh charged cells and touch the metal plate of the Cree. Hot or sizzling hot?
-hopkins

 

[Mitica]

The body of lamp is all plastic. I guess that even if you put a heatsink inside the heat is trapped inside. I was thinking to put a coin as heatsink, cut a small hole inside the plastic body and take the margin of coin outside
Also there is no high.. there is just 5 mm leds on or 1 P4 on.

 

[hopkins]

I bought some aluminum at the hardware store and cut a piece that acts as a heat pipe to cool the Cree in the Smith&Wesson 3aaa headlamp.
I cut a Slot in the headlamp. Lucky there was just enough room for this.
It really works. The heatsink gets very hot. Bike riding air flow would make fantastic cooling.
Maybe something like it could be done to yours.
-some pics
http://www.postimage.org/image.php?v=aV1fB11S
http://www.postimage.org/image.php?v=aV1fB8wi

 

[pxbaroni]

I am not sure what the advantage of the heatsink is for my purposes. The light is primarily used while running or riding and seems to never get hot. Is this something that helps battery life, or the life of the unit? PS, for the money this unit is great...run time is plenty long for what I do.

 

[KnOeFz]

I bought my girlfriend this light before a camping trip this summer as she mentioned a few times how we could really use a headlamp (don't ask why she had to mention it a few times before I bought one :shrug

The build quality is ok and it feels good on your head. While using is we found the cree is really bright so try to avoid having that switched on if you want to talk to people ... they'll be blinded. So it's really nice to have the cree for walking over the campsite and use the 5mm leds for reading, making dinner and stuff.

With 4 aa's the runtime is plenty and I was kind a surprised the light is used as much a she does.

So far the lack of heatsinking which could damage the led with overheating hasn't caused any problems, but then the light is mostly uses with the 5 mm leds switched on....

:twothumbs

 

[hopkins]

As with all LEDs, there is a direct relationship between the LED junction temperature and the permanent loss of light output over time. Running XLamp LEDs at higher junction temperatures will decrease the useful LED lifetime. In general, the following three system-level factors greatly influence the LED junction temperature:
1.operating current
2.ambient temperature
3.thermal resistance of the thermal path to the ambient environment

above from this CREE document
http://www.cree.com/products/pdf/xlamp_reliability.pdf

and if the CREE is sealed inside with no path for the heat to escape?

 

[hopkins]

here's some CREE cooling data. Basically a sealed, waterproof, plastic headlamp violates all the rules CREE lays out for applications of their LED's

http://www.forge-europa.co.uk/pdfs/XLampThermalManagement.pdf

 

[Mitica]

I was looking at PT EOS pictures and seems to have the same problem.
Anyway in DX headlamp I guess the led has no more than 350mA on input

 

[hopkins]

I agree that at lower current levels the LED inside a sealed plastic headlamp
with no heat path to the outside will probably be ok and stay 'alive'
for its estimated life.

But the estimated life calculation performed in a lab at 1amp and a water cooled giant heatsink in not real world.

But what is that breakpoint in current flow for this type of lamp with no
heatsink?

 

[drmaxx]

Thanks for the reply…any chance you have a minute to explain the voltage issue. As I said, I am not knowledgeable...however, mathematically it seems that 4 x 1.2volts = 4.8 volts and 5 x 1.2volts = 6 volts. This light is a 6 volt system. 4 alkaline batteries = 6 volts, not 4.8, and that is what is in the light now although it runs with nimh batteries too. Do nimh batteries drive power differently? Help is appreciated...I am trying to get up to speed on this stuff.

Check out this thread:
http://www.candlepowerforums.com/vb/showthread.php?t=213029

 

[nzgunnie]

I am not sure what the advantage of the heatsink is for my purposes. The light is primarily used while running or riding and seems to never get hot. quote]

That just means the heat is being trapped inside. A light that gets hot to the touch is radiating that heat away, a Cree light that stays cool is trapping all the heat inside.