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# How do i go about running LED bike lights from a 12V Battery? Answered

Hi All,
Need your help with trying to come up with a way to run 3 led bike lights from a 12v 0.8ah battery.  I have looked at a variable voltage regulators, but have been unable to find one that suit my needs.  The actual battery that I am using is in the below link:
http://www.batteriesplus.com.au/pd/803/273/century-ps1208/

Each bike light runs off 3 aaa batteries (4.5v)

Any ideas would be appreciated.

Yes I can read a schematic and solder

Cheers.

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## Discussions

Here is an instructable using a DC to DC converter:

https://www.instructables.com/id/93-efficient-DC-to-DC-Converter/

The data sheet says the input voltage can be 4.5 to 14 volts. The output can be adjusted from one half volt to 6 volts. Murata makes several different devices for different current / wattage requirements;

http://www.futureelectronics.com/en/Search.aspx?dsNav=Ntk:PlainTextSearch%7coktr%7c3%7c,Ny:True,Nea:True. Make sure your input voltage does not exceed 14 volts and these will work fine.

You need to make some decisions first.
• A series pass regulator would easily work with extreme simplicity of circuit schematic which you can easily Google using an LM317.
• A switcher down regulator ( more complex circuit ) would also work but with 2.5 times the length of operation of a series pass regulator from the same 12V battery.

A

Hey Iceng -  Since I'm simplicity incarnate, the fisrt idea sounds good! A couple of questions: do I need to add the capacitors? and also, do i have to build one of the curcuits for each led bike light? The curcuit below is what I was thinking of buliding.

If I want to achieve 4.5v from 12v, by my calculations I would need a resister value of 150 for R1 and a trim pot 400 - does this look right?

Yes it is correct. R1=150, R2=392, resulting in Vout = 4.52
using this calculator with purchasable 1% resistors (no pot needed).
You can use one regulator for all three or put one in every bike light..
I would add the capacitors but the input capacitor is most important.
Good job !

I included a PDF for the LM317.

A

Perfect - Thanks Iceng.
Once I get this up and running i'll have to post a Instructable.