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Methods for Powering 8 LEDs? Answered

Hey Guys - My daughter has a small Little Tikes car which I'm adding 8 LEDs (3 per headlight & 1 per taillight) to. Each LED is a 2v 20ma. I've already started, but hit a snag. For testing the LEDs, I used a 9v battery with a 330ohm resistor on positive. This lit individual LEDs as well as 3 LEDs in parallel. My plan was to wire them all in sequentially then figure out what was needed resistor wise when done - bad decision. I have almost everything installed except power and now stuck as to what do do. Having 8 LEDs which are 2V / 20ma, exceeds the voltage a 9V battery can produce. Afraid to try connecting the 8 directly to 9V as don't want to risk burning them out. Just wanted to post to see what my best option would be - especially one where I wouldn't have to rewire everything again in parallel if at all possible. Thanks!

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Downunder35m

27 days ago

I assume they shall be all on at the same time?
3 LED's in series requires 6V and 20mA.
A 47 or 56 Ohm resistor would be fine then on 9V.
2 LED's in series need 4V and 20mA.
Two 560 Ohm resistors in parallel come down to 280Ohm and should fix that one.
Connect head and tail lights in parallel and you need about 60mA to run them.

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bzowkDownunder35m

Reply 13 days ago

Thanks for the reply...

Yes, the plan is to have all come on at once via a single switch. I think you may had missed that I have 8 LEDs total - not 5 - as each headlight has 3 in a series. If you accounted for this, below is how I interpreted it:
1. Keep 3 LEDs in each of the two headlights wired in series with a 47 or 56 Ohm resistor connected to positive end of each
2. Connect pair of headlights (above) in series (which from left -> right with positive 1st would result in a transistor, 3 LEDs in series, transistor, 3 LEDs in series)
3. Keep taillights (1 LED each) wired in series
4. Wire headlights series and taillight series in parallel
5. Connect pair of 560 Ohm resistors in parallel to positive of power source
6. Wire power source in parallel with LEDs in parallel from step #4

Thanks