Regarding LED can light electronics

[AquaticLung]

Hi, I'm hoping some of you may have experience in the cannister lights newer LED technology. I've recently acquired a DIY can light. So maybe you can help? The light I have is made from a mag light head and a professionally manufactured cannister, you've probably seen similiar lights on ebay lately. The light is decent quality for a non-standard assembly, but the design is very similiar to what you would see from a reputable manufacturer. So I'm looking to build a few extra battery packs for the unit. What I'm unclear about is the LED power supply specs. It uses a SSC P7 single LED and a 2.8 Amp 5-state driver. I'm not sure the power of the current battery packs, but they are Li-Ion 18650 cells; 2 packs with 4 cells each. What I need to know is what advantages/disadvantages in selecting certain battery cells. I'm wandering if I have to stick with a certain voltage or if the number of cells determines the voltage and if I choose a 4000mAh set of cells over, say, a 2600mAh set will my light burn longer, brighter, both, or am I limited by the driver and have to stay within a certain max mAh? I'm aware that the driver is determined by a specific LED, so I need to know what the max capacity battery I could use and would best serve me in regards to burn time and brightness... This might be way off course, but I was thinking that the 2.8 Amp driver was maybe a limiting factor and each cell has to be under that spec of 2800mAh. It would be extremely helpful to know if I'm way off in these conclusions? Many thanks....

Cheers

[350xfire]

The best way to determine what your LED is using up is to hook it up to a lab power supply. Then apply voltage and see what the current is doing...

If you don't have one, then check battery voltage. I bet it is a 7.4 volt pack with 2 serial and whatever many sets in parallel.

Battery capacity has nothing to do with anything except for run time... Battery voltage, however, does have to do with how the light will run. If you go too low, the light will not fire or will be dim. Too high and the driver may over heat and bur up or not work due to internal protection. So keep the voltage at what the light came with.

Typical LiIon battery capacity is about 2500 mah. Do not get any of the 3000mah as they are not rated for high rates of discharge.

[Chilly_Dipper]

Ok starting off the voltage is what you have to worry about with your battery pack selection the load (ie the electronics and led) will determine how much current is drawn. 350x is correct in ensuring that your batteries can discharge at an appropriate rate BUT it should be noted most LED systems don't draw a whole lot of current usually so this factor is not normally a issue. (Notice I said NORMALLY)

One way to determine the electrical characteristics of your battery pack is to use a multimeter. To measure the voltage of your battery pack place the leads of the meter across the terminals of the battery pack when it is set to DC measurement.

In order to measure current you have to measure the current with the meter in series with the circuit when it is operating. Alternatively you could use a clamp meter but they aren't as accurate as the direct measurement method.

The voltage in each cell of the battery pack is determined by the type of materials it is made of Nickel Cadmiums (more than likely what in your light) have a nominal voltage of 1.2V while lithium ion is around 3.6V. You should also know when fully charged a battery will read above its rated voltage unloaded ie lead acid battery like the one in a car is a nominal voltage of 12V BUT when fully charged will read ~14V.

I hope some of this helps if you have any questions feel free to ask

Cheers,
CD