This is a way to let people see you at a distance while riding your bike at night. Simple to make, instal and use.

Step 1: Things you will need

Altoids box, 12 volt switch, multi tool, 2 9 volt battery conector tops and a sodering iron and of course 12 volt leds for an automobile (water resistant)
somebody stole yout instructable
I thought you get more power from batteries connected in parallel than in series but the drawback would be shorter usage time because in parallel the batteries would drain quicker. Correct me if I'm wrong because I want to get my facts straight too. thanks
in series you get more voltage but in parallel, you get more battery life. power is constant in both cases. but in the parallel situation, the amperage is doubled. while in the series, the voltage is doubled.
I was not worried about battery life. A single 9v olt kinda works, but 2 9v batteries make the led glow at a good distance....
If you have prewired led's that are supposed to run off 12 volts and you give it so much amperage, you risk burning the LED's out, or at least severely shortening the life of the lights. you mentioned that the led's are brighter, that comes form over driving them. the reason that the single 9 volt is not as bright is because the led's are made to work at 12 volts. To be safest, i would get a battery pack and add AA's or similar batteries to hit 12 volts as intended by the light manufacturer.
I agree. LEDs are not very tolerant of too much/too little voltage. If you're going to hook up 2 9V batteries (desirable due to size), then you want to add resistors to bring it down to 12V.
Bringing 18v down to 12v using resistors is absurd....you do realize that the 6V drop is dissipated into heat and is there for wasted energy from the battery? putting more LEDs in series will get you closer to that 18V mark and give you maximum light output vs electrical input. To sum up my point with a solution....instead of the resistor dropping the voltage, use LEDs.
thanks for the info...it really helps
Are the LEDs wired in series also? How many can you power from 2 - 9v? No dropping resistors? Thanks.
I picked them up pre-wired at an automotive store for $12.. 2 sets of four lights.
Why not using the bike itself to generate power?
Most generators are only 6v, I found a Chinese one that is 12 v, but the big draw back is the light go off while stopped. I only ride at night so hi vis is important to me.

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