wifed
...it's our mountain now
How to...
build your own 20Watt halogen lights for under £30
This makes 2x10 watt halogen spot lamps, with one lead acid battery. The burn time depends on how much weight you are prepared to carry around with you. For a little more expense this system will happily run on NiMH batteries or lithium ion, though lithium ion cells are expensive. A shop bought lithium ion system would still cost 3 times as much (though it will be a little less ugly).
However, with lithium ion cells you will have to use some resistors in the circuit to protect the bulbs as it will be 7.2 volts rather than 6. I will go into that a bit later.
For the basic lead acid system you will need.
Tools:
- 1 pair of pliers
- A small drill (I managed with just the drill bit, the casings are quite soft)
- 1 soldering iron
- A screwdriver (to suit your screws)
Materials - Plumbing fittings:
- 2x 32mm screw fit pipe connectors as pictured in (fig 1)
- 2x blanking plate to suit connectors. Shown with hole already drilled (fig 1)
- 2x 22mm pipe clips (fig 1a)
- 2x tap washers (fig 1b)
- 1 roll PTFE tape (plastic tape for engineers)
(fig 1)  |
(fig 1a)  |
(fig 1b)  |
Materials - Electrical:
- 2x10w 35mm halogen projector bulbs (fig 2)
- 2x lamp holders (fig 2)
- 2x power connectors (fig 2a)
- 2x power sockets (fig 2a)
- 1 length of 6amp mains cable (as long as you need)
- Heat shrink sleeving (or tape if you're lazy)
- A couple of crimp tags to attach cable to the battery (not shown)
- 1x 6Volt, lead acid battery, capacity depends of desired burn time (not shown)
- 1 battery charger (not shown).
(fig 2)  |
(fig 2a)  |
Other stuff:
- Some short self tapping screws
- Silicone sealant for water proofing cables
What to do
1
Screw the pipe clip to the outer casing of the 32mm pipe connector (fig 3)
(fig 3)
2
Drill hole in the blanking plate, solder lamp holder onto power connector and fit it to the hole (fig 3a)
(fig 3a)
3
Unscrew the end from the pipe connector, push the lamp holder though the inside, screw the end back on to hold into place and clip the bulb into the lamp holder (fig 3b and fig 3c)
(fig 3b)  |
(fig 3c)  |
4
Your lights should now look like the one in (fig 3d) Fit your tap washer into the other screw end of the pipe connector (fig 3e, fig 3f, and fig 3g)
(fig 3d)  |
(fig 3e)  |
(fig 3f)  |
(fig 3g)  |
5
You should now have a completed light looking like this.
Now all you have to do is make your cable
(Sorry about my lack of photos here, my cable is already made, I will post more should I need to build another)
1
Cut two short lengths off the end. These will make your "y split" to plug into the lights.
2
Strip back one end of each short cable and one end of the long piece.
3
Place some heat shrink over the exposed cores of the long cable.
4
Solder all the blues together and all the reds.
5
Slide the heat shrink over the joint and heat it to shrink it into place. (if you cant get heat shrink tape will do)
6
Your joint should look like this.
7
Case the joint in tape to hold it fast.
8
Solder the power connectors to the short ends.
9
Before screwing the sleeve onto the connector pump silicone sealant into the sleeve and around the solder tags. This will keep it waterproof.
10
Solder AND crimp the crimp connectors onto the long end.
Congratulations, you have now got 20 watts of halogen light for under £30.
Now the heavy bit. Batteries.
The weak link in this chain is definitely the batteries, namely cos of the weight. As I said, you can use NiMH batteries or lithium ion But as the weight comes down, so to will the cost go up.
So let's do a little bit of maths and work some burn times out.
Burn times.
A 6 volt 10Watt bulb draws about 1.7 amps of current, so therefore two bulbs will draw 3.4 amps.
So you need a battery that’s going to give you a decent burntime. On the face of it a 3.4Ah battery will give you 1 hour of burntime with both lights running, right? Wrong I’m afraid. You also have to consider that as the battery drains the lights go yellow and dim due to the voltage dropping. So what you’re concerned with is how much “useable” light you will get. In reality you will probably get half the calculated burntime out of a battery before the light is useless to you, especially when it’s cold.
The following table shows approximate burntimes of “useable” light.
| Capacity of battery | Burntime with one light | Burntime with two lights |
|---|---|---|
| 4.2Ah | 1.25hrs | 40 mins |
| 7Ah | 2 hrs | 1hr |
| 10Ah | 2hrs 55mins | 1.5hrs |
| 12Ah | 3hrs 3mins | 1hr 45mins |
This is based on (capacity/current)/2
These are very approximate as a lot depends on things such as air temp and such.
Nimh Batteries will follow similar rules, but will give marginally better burntimes.
For lithium ion cells you will need to add a resistance to the circuits in order to protect the bulbs.
I'm not going to get into the mathematics of it, as I have no idea how to type the formula used.
In short, a lithium ion cell is likely to be 7.2Volts, which is far to high for your 6V bulbs to handle. So we need to place a 0.9OHM resistor in series with both bulbs. The best place to do this is inside the light between the power socket and the bulb.
This will drop the current flowing and bring the voltage across the bulb back down to 6Volts.
Good luck building and happy riding?
Coming soon...
Luxeon LED lights (as soon as I work out a decent way to mount em)
Deep discharge protection for batteries (as soon as I can be arsed to figure it out)