Simple LED wiring help

[guitarguy89]

Alright so,
I've done a few small wiring projects before but I can't really figure out what's going on.
I just bought my girlfriends son one of those 12V ride on cars for kids. It works great and he loves it. But I got the wise idea to ad lights to it. So I drilled out the backs of the headlights and side mirrors, as well as the brake light in the spoiler. Altogether I'm running 6 5mm red led's and 2 jumbo white ones. (I believe they are 10mm) so when I hook up the power to the 12v battery, nothing.
Do I just need more power?
I have all of the positives wired together and all the negatives wired together

 

[DerStrom8]

Wiring LEDs is not really as simple as connecting all the positives connected and all the negatives connected. You must make sure that your LEDs are not backwards. If you look on each side (above the leads), you'll notice one edge is flat. That is the cathode, which is hte negative lead.

LEDs are current-driven devices, not voltage-driven. They also have a very low internal resistance, which means if you hook them up directly to a power source, with nothing to limit the current, you'll destroy them almost instantly. It's quite possible you already did this. You really need a resistor in series with each LED, and in order to determine the necessary resistance, you need the datasheets for the LEDs. You should be able to get the datasheets from the supplier.

Once you have them, post back here and we can continue. First step would be to test them and make sure you didn't destroy the LEDs already, but you still need the datasheets for that.

Regards,
Matt

 

[KeepItSimpleStupid]

Each LED needs it's own series resistor. Without a datasheet, a resistor less than (12-3)/20e-3 ohms is a decent guess. The power dissipation of the resistor needs to be checked too, but probably a 1/2 W resistor should work. P resistor > (V^2)/R, (12-3)/R The 3 is the Vf spec of the LED, the 20E-3 is 20 mA of If of the LED.

 

[audioguru]

Since the battery is 12V (13.8V when charged?) and red LEDs are about 1.8V and white LEDs are about 3.2V then three red LEDs can be connected in series and in series with a 390 ohms/one-quarter Watt resistor.
Two white 10mm LEDs can be connected in series and in series with a 220 ohms/one-half Watt resistor.