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Making Bike Lights

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I have been using a combination of home-made 12V halogen lights on the front and "giant" LED lights on the rear of my bikes for over a year now. Most electronic supply places sell cheap 12V sealed lead acid batteries (SLA) and small wall-wart type chargers that will fit them. Then all you need is some wire, a few plugs, and a light. The rear lights have 18 LED's and take 4AA batteries, which last quite some time (more than 12 hours continuous). I also use NiMH rechargeable AA batteries so the exact run time isn't hugely important to me. All that comes from Jaycar , one of the cheaper electronics shops in Australia. I have started using cordless drill batteries, rather than using a sealed lead acid one. Note: This page is also available as an easy-print flyer.

trisled light
TriSled light mount
To the left is a collection of plumbing fittings bought from a hardware shop by the simple expedient of wandering round said shop with a halogen bulb playing with things until I found what I wanted. It's got a custom mount brazed on, because I could. Mounting lights onto a recumbent is usually a bit of

The front lights are fairly easy to make up, and with practice it takes me less than two hours to go from a pile of bits to a working light. The bulb can be the hard part. You want a 12V 20W halogen light, which most lighting shops have, and also some electronics places. Beware of 50W lights, and also of "bike lights" that typically run on 6V and are less than 10W. Once you've got the bulb you need a way to hook that to your bike. I've seen bits of PVC pipe used, but also a plastic tow ball cover that worked well too. The advantage there is that a couple of hose clamps hold it on really easily - one round your handlebar, one round the tow ball cover. The bulb goes in the cover and a couple of bits of bent aluminum under the hose clamp hold it there. Remember that you don't need waterproof, just shower proof, and try to keep the back of the bulb dry. These things come with a reflector built in, and so the hot bit is sealed away.

Here's a shot of my simple mount for a halogen onto my bike. It's just a bit of old spoke bent round the back of the light and bolted to the frame. The spoke goes round the base of the bulb then forward and hooks over the front slightly. I have three of these in operation with the oldest being about two years old. The main disadvantage seems to be that on an upright bike there is a distracting amount of light coming out of the bulb so you need to either rig up a shield or paint the bulb silver on the back.

photo of front light on my tandem trike
front light on my tandem trike

On the tandem I used the simple bent spoke mount shown above. The halogen globes all seem to have a groove each side of the base, so I bend a wire into a square-ish U shape so that the two sides grip those grooves. This works remarkably well for such a simple system (ie, I haven't felt it's worth while coming up with a better one).

For charging you really want plugs that only go together one way, and in use they need to handle 2A or so (2A for a 20W bulb, 5A for a 50W one). I use the cheap ones from Jaycar that will cope with 50A - they're used on radio controlled cars to connect the battery to the motor (Jaycar part numbers at the bottom of the page). Then wire a socket to the battery. Hook one plug to the bike running the wire through a switch to the light. Then put the other plug on the charger. That way even after a long day you don't accidentally hook the charger up backwards and wreck your battery. Jaycar sell a smart charger that switches over to trickle when the battery is charged, and has an LED to tell you it's working. An alternative is a cheap plug-in timer, the sort you plug in, then plug your appliance into the other side of. So you set it for 4 hours or whatever, plug in the charger, and forget it.

Oh, timer charging. I usually charge for about 20%-50% over the rated capacity. So a 4.5AH battery on a 1A charger I set for 6 hours. That happens to describe my system exactly :) If you want to do better than that you need a voltmeter. Charge the battery, measure the voltage off the charger (it should be the rated voltage on the side of the battery, 13-odd volts for a 12V lead battery). Now hook the charger back up, turn it on and measure the voltage again. Now you know what voltage you get on charge when the battery is fully charged. In future you can stop charging when you get here. It is much easier to just buy a smart charger and let that do the work (and more accurate).

Giant rear LED lights

rear light mount on TB2The rear light I use is a car emergency light or some such thing, and it lacks the standard bicycle mounting attachments. I've seen several ways to mount them, ranging from bent coat hangers through clear themoplastic to the bolt-on ones I prefer. I drill a couple of holes in the back and bolt strips of aluminium to the light. These hook over or onto the bike in the traditional way. On one bike I have simply removed the 3mm screw that holds the rear cover on and used a longer bolt to hold the light onto a plate brazed to the bike. That's the advantage of building the bike too... The mount on Tall Bike Two shows what I usually do, with the back plate of the light in place - albeit in this case the custom bike got a custom mount.

Since I use AA batteries in a variety of things I tend to carry a fair few everywhere, and I have at least 40 NiMH AA batteries around the place. My digital camera takes four of them at a time, so I take all the batteries and the charger when I'm touring. This also means that I can run other lights as backup, so I have a few 2AA LED rear lights, a 2AA white strobe and a Cateye Micro (4AA) for touring (not as much light as the big halogen, but much easier to carry). I'm a big fan of "spare" lights, not least because it's hard to estimate the distance to a flashing light so you really need both a flashing rear light and a constant one. I usually run the big light in constant mode, partly because it's not a lot of fun to ride behind one when it's flashing.

Jaycar part numbers and July 2001 prices

Front light
Description Code Cost for oneCost for ten
12V, 4.2AH SLA Battery SB-2484$39.50 $31.45
12V SLA smart charger MB-3517$32.95 $26.45
12V 20W halogen bulb SL-2730$5.99 $4.75
socket for bulb SL-2735$3.75 $2.95
medium duty speaker wire- 2mWB-1706$1.30 $6.50
female spade connector PT-4507$2.20 $19.50
terminal strip HM-3196$1.85 $1.65
2 pin plug/ socket (need 2)PP-2020$2.25 $1.95
Rear light
Description Code Cost for oneCost for ten
Giant LED light ST-3039$28.00 $22.35
AA NiMH (>1500mAH) SB-2442$4.30 $3.75
smart charger, up to 10 AAs MB-3512$69.95 $55.95

I do occasional bulk orders for these things for Critical Mass Sydney , where we get a further 10%-25% off the 10+ prices. There's some useful stuff on the net about NiMH batteries - both Energizer and Duracell have pages up.