Instructables
This project is a home-built bike light using Malibu sidewalk flood lights you can buy at Home Depot or most hardware stores. The project is inexpensive to build and easy to do. My first Malibu light has held up well in some really challenging conditions like several bike falls, dust storms and rain so I feel confident about it's general utility.

They put out a good amount of light compared to LED bike lights. I have a LED light on my helmet for extra backup which is an excellent idea. The bike-mounted light points in your direction of travel and is very visible to vehicles and other travelers. The LED helmet light is a backup and points in the direction you are looking at, like your bike lock at night or a car in your vicinity.

More light is better for anyone traveling at night.

 
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Step 1: Get the parts

The light is a standard Malibu light available in most places that sell lighting. It's used for lighting sidewalks.

This unit is a slightly higher end model at $15 compared to the $9 units I've used previously. The advantage of this unit is that the cheapest Malibu has an extended light barrel on the end of the light which is a stylistic add-on I think. The barrel has an extended lip on top. If you hang the light upside down on your bars, the barrel can be rotated but the lip won't be at the top of the light. Annoying.

Also, the light below is using an MR16 bulb and seems to put out more light at the same wattage than the lower end Malibu. Plus the body has ribs.

The light also has an adjusting screw that you can loosen then rotate the light vertically. That's a big help when you're dialing it in.

So, one Malibu light.

Some lamp cord. Long enough to go to wherever you plan to put your battery plus some extra slack.

I'm using a lighted switch below. You can also use a lamp cord switch for $1. That's cheaper but has the drawback that there's no visible signal to you that your light is on. You'll find out why that's important the first time you have your light on in somewhat bright conditions and forget to turn it off, draining your battery.

The connectors are called Powerpoles. They are genderless and work pretty well. I don't like the look particularly when they are exposed but that's what I'm using until I find another way.

Some folks use stereo plugs.

The switch is mounted on a conduit hangar. It's basically a metal u-shape that has a oval in the middle that fits most handlebars handily. The screw is behind the lamp cord in the picture. Very cheap and easy to use.

12V lead acid battery. I use these because they are inexpensive with good capacity.

The 7.5 amp hour batteries have thinner profiles than the 4.5ah or 12ah ones. I use them because they are a nice middle range between the 4.5ah (easy to mount with lower capacity) and the 12ah (big, heavy bricks).

I fuse my batteries because there's nothing like getting electric current through delicate body parts to ruin your whole day, not to mention catching on fire or getting a nasty burn.

So, one blade fuse available just about anywhere. I use a 10amp fuse. The fuse should be 1.5x greater than the amps in the circuit. so I guess it should be 20watts=12Volts x Amps = 1.6Amps in the circuit times 1.5 = 2.5 Amp fuse nominal.

The switch is a lighted switch for 12V circuits. i found one at an electronics store.

You'll also need a charger for your battery. I found an inexpensive one at an electronics store. The charger has to match the type of battery you are using. It's better to pay a little more for a charger than get the cheapest one you can find.

So:
Light - $15
Switch - $3.50
Conduit hanger - .50
Lamp cord - $2
Battery (ebay) - $20 w/delivery
plus a couple of crimp on connectors for your battery posts, plus maybe some electrical tape.
Charger - $15 - $50 depending on what type you get.

diode_tensegrity (author) 3 years ago
A 5 amp hour battery + 20 watt draw at 12 volts run time? It's drawing 1.7 amps. I'd say an hour to 1.5 hours. You're going to want to recharge the battery when you get back. If you run it down and let it sit, it will kill the battery.

Brian_B3 years ago
I realize this is an older instructable, but I am new here.

If the person who posted this is still around, would you give me some idea how long the type of battery in the picture lasts with the 20 w 12V light?

I have found several places that sell them pretty inexpensively (about that size).

I have the same type of bike, except the trike version. I need a bright light. I do not need hours and hours of light. Just evening rides.
bikinearly5 years ago
I have made a few of these myself. I tried auxiliary driving lights with good luck. The newest attempt was a 50 watt halogen Malibu style floodlight. The 7.4 a/hr sla battery will run for about an hour at this rate. For recharging my battery I have been using a automobile battery charger with the auto-shutoff at a charging rate of 2 amps per hour. The battery lasted about three years at this rate of abuse. Mounting the light and the battery is an adventure.
diode_tensegrity (author)  bikinearly5 years ago
50 watts....that should light up the road pretty well. The most I've done so far is 20 watts. I had a bunch of NIMH D cells I had used for an electric bike. I took them down to Batteries Plus and they shrinkwrapped and soldiered them into a pack for only a few bucks. 10 of them make a 12V battery. Nice way to keep using an otherwise used up bunch of batts.
i have these cygo lights, these will blind you momentarily, and it'll hurt, 6volt battery pack, 2 lights, pretty bright
Woody716 years ago
Could the original light bulb be replaced with LEDs? I'd like to conserve as much battery life as possible without sacrificing candlepower. :)
diode_tensegrity (author)  Woody716 years ago
You could certainly replace the light with LED's but there lies the rub. If you use high candlepower LED's, like the Luxeon, the price is going to shoot up. You could make a bank of LED's and put it in the lamp but the candlepower may still be lacking. There are some other instructables where they make LED bike lights. This project is meant to be dirt simple, give great light and be easy to run.
LasVegas7 years ago
The wire from the switch to the negative terminal of the battery is unnecessary and should be removed. There is no reason to short the leads of the lamp.
You're assuming that this is a toggle switch, DPST. The third leg (terminal, contact, whatever) is because there is a light inside that needs to be powered.

I'm assuming that the manufacturer didn't put everything in series (so that the light will only turn on when current is flowing through) in case you needed an indicator that the switch was on, but it didn't necessarily close the circuit. (let's say you needed this and another switch to be closed, and the other wasn't closed yet.) This way, the switch can be lit (closed) without needing the circuit it's controlling to be closed.

Here's another example. http://www.radioshack.com/product/index.jsp?parentPage=search&summary=summary&cp=&productId=2062522&accessories=accessories&kw=lighted+switch&techSpecs=techSpecs&currentTab=techSpecs&custRatings=custRatings&sr=1&features=features&origkw=lighted+switch&support=support&tab=summary
diode_tensegrity (author) 7 years ago
Las Vegas, You don't say why that's true. The switch has an internal light which turns on when the switch is on. One of the three posts is the negative pole of the internal light. If it doesn't go to ground, the light won't go on. I think I explained that throughly. If you have a schematic or explanation that explains your comment, I will edit the relevant section.
HamO7 years ago
Well done, nice instructable, great pics and good idea!!