12dcV to 2dcV? (car battery to +220 LED's)

[pointblank9957]

Ok heres the dilema, i have over 220 3mm leds in the rear reflector of my car spelling "ECLIPSE", each are rated @ 2.1v & 20mA. I'm going to be running them with a relay from my marker lights. To reduce the voltage, would i need 2v .5a Zener Diodes? The leds are all in parallel, totalling 4.4a draw. So i would need 9 .5a 2v Zeners in parallel from the source? Zeners are very cheap (25 for $.99) and i bought the leds (1100 for $15)

heres a quick schematic to get the idea:

 

[duke37]

Your circuit is not suitable. Leds or zener diodes should not be placed in parallel since one may take all the current until it pops.

I would suggest that you place four leds in series to give 8.4V. The excess 3.6V can be dropped with a 180 ohm resistor passing 20mA.
You will need 55 strings at 20mA so the total current will be 1.1A, I do not see the need for a relay.

 

[pointblank9957]

Your circuit is not suitable. Leds or zener diodes should not be placed in parallel since one may take all the current until it pops.

I would suggest that you place four leds in series to give 8.4V. The excess 3.6V can be dropped with a 180 ohm resistor passing 20mA.
You will need 55 strings at 20mA so the total current will be 1.1A, I do not see the need for a relay.

the relay powers the leds when it senses the taillights come on, so theyre not on all the time. and all 220 leds are already soldered in parallel

 

[duke37]

The leds can be connected to the tail light circuit where the relay would be. About 1A extra should not be a problem and you will have a fuse in the circuit which will reduce the chance of fire.

You will need to connect the leds correctly so strike while the iron is hot.

 

[(*steve*)]

Even if you wanted to keep all the LEDs in parallel, each should have their own resistor (so they're not directly in parallel).

Have you seen LED lights on cars where some appear to be brighter than others, and some are not turning on at all? That's because they've been wired the way you've done it.