Thomas Wright
May 19, 2003, 04:01 AM
Using two in series will make them too dim (6v/2 = 3, less than the required
3.5) but you could put a resistor in series with an LED to give the right
brightness. Here's how to work out the resistance you need:
R = (supply voltage - LED voltage) / (LED Current)
so in this case...
R = (6-3.5) / (0.03) = 83 ohms
R = (6-4) / (0.03) = 66 ohms
where 0.03 is 30mA in amps. So it looks like something around 70-80 ohms
will suit fine. You may not be able to get a resistor exactly in this
range but you can build it up from other resistors if you have the
space/patience.
HTH,
Thomas
Adam J Flemming wrote:
>
> Hi All,
>
> I need some help with elementary highschool science here. I want to add
> some LED headlights to my RC model, running preferably from the powerpack
> on board (6 volts).
>
> The LEDs that I'm currently looking at are.... courtesy of the Dick Smith
> web site...
>
> Lens Size: 3mm Round
> Emission: White Light
> Output: 1100mcd (min), 1500mcd (max)
> Viewing Angle: 30
> Lens Type: Water Clear Epoxy
> Forward Current: 30mA
> Forward Voltage: 3.5V (typical), 4.0V (max)
> Reverse Current: 50uA @ 5V
> Peak Forward Current Duty Cycle 1/10 @ 1kHz: 100mA
> Power Dissipation: 120mW
>
> Now, if I try to put 6 volts through one of these, chances are, it'll be
> really bright for about half a second, followed by eternal darkness.
>
> If I use two in serial though, do you think this may just offer the
> resistance I need without blowing both?
>
> I'm pretty much considering just getting a 2-aa battery holder and using
> that, as it'll supply a nice 3 volts for the LEDs.
>
> Anybody done this (daft question, I know)?
>
> Cheers,
>
> Adam.
3.5) but you could put a resistor in series with an LED to give the right
brightness. Here's how to work out the resistance you need:
R = (supply voltage - LED voltage) / (LED Current)
so in this case...
R = (6-3.5) / (0.03) = 83 ohms
R = (6-4) / (0.03) = 66 ohms
where 0.03 is 30mA in amps. So it looks like something around 70-80 ohms
will suit fine. You may not be able to get a resistor exactly in this
range but you can build it up from other resistors if you have the
space/patience.
HTH,
Thomas
Adam J Flemming wrote:
>
> Hi All,
>
> I need some help with elementary highschool science here. I want to add
> some LED headlights to my RC model, running preferably from the powerpack
> on board (6 volts).
>
> The LEDs that I'm currently looking at are.... courtesy of the Dick Smith
> web site...
>
> Lens Size: 3mm Round
> Emission: White Light
> Output: 1100mcd (min), 1500mcd (max)
> Viewing Angle: 30
> Lens Type: Water Clear Epoxy
> Forward Current: 30mA
> Forward Voltage: 3.5V (typical), 4.0V (max)
> Reverse Current: 50uA @ 5V
> Peak Forward Current Duty Cycle 1/10 @ 1kHz: 100mA
> Power Dissipation: 120mW
>
> Now, if I try to put 6 volts through one of these, chances are, it'll be
> really bright for about half a second, followed by eternal darkness.
>
> If I use two in serial though, do you think this may just offer the
> resistance I need without blowing both?
>
> I'm pretty much considering just getting a 2-aa battery holder and using
> that, as it'll supply a nice 3 volts for the LEDs.
>
> Anybody done this (daft question, I know)?
>
> Cheers,
>
> Adam.