1st Quad Cree P4 Bike Light Project

[GeneralTao]

I am a flashlight collector or a flashaholics and also a newbie in electronic. I am trying to build my first bicycle light project with four Cree P4 bin LEDs. How can I connect the all the Cree LEDs together in a series connection at 350mA, 500mA, or 1000mA?

I have a series of questions and I need someone to help me solve it?

1) Cree website mentioned each LED has a typical 3.7V Forward Voltage at 1000mA; does it matter when choosing the 350mA, 500mA, or 1000mA, does it reduce the life of a LED?

2) I have used the LED Pro 2.12 program and I've got a -2.8 Resistance in Ohms. What is -2.8 resistor wattage means?

3) Do I need to add other components into my series circuit like resistor?

4) What kind of battery I should use and the voltage?

5) Which is better to use optics or I can just use the smooth reflecting cups?

 

[penquissciguy]

I am a flashlight collector or a flashaholics and also a newbie in electronic. I am trying to build my first bicycle light project with four Cree P4 bin LEDs. How can I connect the all the Cree LEDs together in a series connection at 350mA, 500mA, or 1000mA?

The LEDs have two leads, + and -. You solder wires between them to connect the - of one LED to the + of the next. You should be left with a + on one end of the series of LEDs and a - at the other. That's where the circuit is connected to the power supply.

I have a series of questions and I need someone to help me solve it?

1) Cree website mentioned each LED has a typical 3.7V Forward Voltage at 1000mA; does it matter when choosing the 350mA, 500mA, or 1000mA, does it reduce the life of a LED?

Cree rates their LEDs to run at 1000 mA if they are heatsinked properly. If they are kept cool, the operating current won't make a significant difference. The forward voltage of the LED increases with current, so that may factor into your decision too.

2) I have used the LED Pro 2.12 program and I've got a -2.8 Resistance in Ohms. What is -2.8 resistor wattage means?

If I'm understanding you right, you entered a battery voltage in the program that was lower than the combined forward voltage of the four LEDs. The battery voltage must be at least the same as the forward voltage of the LEDs for LED Pro to give a sensible answer.

3) Do I need to add other components into my series circuit like resistor?

Depends on the battery choice. If the battery voltage = the forward voltage of the LEDs, you can "direct-drive" the LEDs from the battery without a resistor. This isn't recommended, as the output of the LEDs changes as the battery voltage drops. Most people include a current regulating circuit in their lights so that the LEDs can be driven at a fixed current.

4) What kind of battery I should use and the voltage?

Many people use either Lithium Ion or NiMH rechargeable battery packs. The voltage of the pack would depend on the type of regulator you use. The forward voltage of your LEDs is approximately 3.7 x 4, or 14.8 volts, at 1000 mA. You could probably direct-drive these lights from a 14.4 v NiMH pack, though a better solution would be to go with either a higher voltage pack and a buck converter or a lower voltage pack and a boost converter.

5) Which is better to use optics or I can just use the smooth reflecting cups?

That's a matter of taste. From what I understand, the reflectors give narrower beam widths, while the optics allow you to tailor the light pattern to your needs.

HTH,

Ken

 

[GeneralTao]

Thank you so much Ken.

I've asked the national.com and I got the reply saying I should use this driver http://www.national.com/pf/LM/LM5022.html

In your application, you should use the 350mA LEDs because they will not drain as much current from the battery. The current drawn by the four (4) LEDs in series with a combined voltage of 14.8V should be close to 1A, hence the battery life can sustain 2-hour continuous operation. The LM5022 should be a suitable driver for this application.


Why is the national person saying I should use 350mA and with a combined voltage of 14.8V should be close to 1A? How can that close to 1A?

Michael