Commuting - DIY budget light lowdown

i'm looking for something to do this week, and a high powered light is the ticket. i had always had a passing interest, and then found this
http://www.instructables.com/ex/i/9129E65EFFBE102880EC001143E7E506/?ALLSTEPS

i tried getting through the 50 page sticky, but the begining was more than 2 years ago and the end has turned into discussions of high output leds. i'm looking to spend less than $30 and have the stuff available off the shelf - homedepot, ace, sears, target are all local (unless its much more economical to order). is there a specific bulb i should look for? how about any tips on battery and charger combos (i'm not going with the AAs in the guide above)? any guides to overvolting? i thought i remembered reading that halogens are actually better overvolted. i'm not sure exactly where i'm going with this...

basically, i would like a cheap DIY rundown of parts. is the mr16 in the guide above a good bulb choice? thanks for any pointers.

I built basically that, but a little cheaper.
I found that the MR16 fit fine just pushing it into the front of the coupler, and I put a PVC plug in the back (I think 1.25" or something). Drilled a hole and put in a switch.

The battery is going to be the most expensive part, especially with the charger. I personally used a 12V SLA (sealed lead-acid, or "gel cell") and a small automotive battery charger. You might find a small 12V SLA for $15 or so, but I've never seen a battery charger for < $25 or so.

You could just get a 15V wall-wart and hook it directly to the battery for charging, but I wouldn't recommend it. You would have to use a timer to avoid overcharging, and if you misjudge or forget or the timer doesn't work right, you'll damage the battery. I think it's worth buying a good charger, you'll only need to buy it once and it makes the battery last longer.

For my 2nd lighting system I used a NiMH bottle battery and smart charger from batteryspace.com, but those alone were about $80. But the SLA and a cheapo charger will get you by until you decide whether to get something nicer. Since I commute 90 minutes a day, at least half in the pitch black on totally unlighted rural roads with 60MPH traffic, I decided it was worth spending $200 or so building a really good lighting system (I used an HID from TrailTech).

Read the "total geekiness" thread. MR-16 Bulb, Optronics housing, SLA battery and charger. Should be right around $30.

I'm extremely happy with my 20 watt 12 degree spot beam MR16 bulb. MR16 is one of the most viable halogen formats useful for bike lighting in terms of efficiency. If you look around, you can usually find an offroading or driving light that uses these bulbs for pretty cheap. There is an Optronics set that can be found for less than $15 for a pair of lights and is about ideal for bike headlight ventures. The model number is QH-7CC, but they are a bit tricky to track down. I found two places that had them when I was looking.

You can find cheal sealed lead acid batteries on ebay. Make sure you buy a new battery and not a used one, as used SLAs are really hit or miss (it might have been salvaged from an emergency exit sign that was manufactured 20 years ago or something). Check the dimensions and weight carefully so you know what you are getting into and have a place to put the battery on your bike. I built a bracket that mounts a 7AH battery inside the frame triangle right above the bottom bracket and it works great and keeps CG lower on the bike.

To decide how big of a battery you need, here is a very crude method: My 20w bulb draws roughly 2 amps of current. We can assume that a 10w bulb will draw 1 amp, and a 35w bulb will draw 3.5 amps. Batteries are rated in amp hours (or milliamp hours). With a 1 amp draw, a 4 amp hour battery will last you roughly four hours. Similarly, putting a 4 amp draw on the same 4ah battery will get you about an hour of runtime. Decide how many hours you will need your headlight to run between charges and calculate the battery capacity needed in this manner. I would recommend a 20w bulb, so you can assume about 2 amps of current draw.

I found a really inexpensive sealed lead acid battery charger that actually has two stages (meaning it cuts out when the battery is fully charged instead of cooking the battery) and is therefore basically idiotproof. Just plug your battery into the charger overnight and by morning the green light will be lit, indicating charging is complete. It runs about $14 from zbattery.com and they also have a 2amp version if you need to charge faster or have a really big battery. The 1amp charger recharges my 7ah battery in a few hours, which is plenty fast for me. http://www.zbattery.com/zbattery/12bc1000d-1.html

All that's left is to homebrew some mounting hardware for the lamp and the battery and wire it up with a switch. I did a lot of experimenting with other parts, but if you cut to the chase and didn't buy experimental parts, here is the breakdown:

optronics housings: $15 for a pair
MR16 20w 12degree spot bulb: $1 to $2 apiece on ebay if you look around (might need to buy 5 or 10)
charger: $14
battery: $5 to $10 on ebay depending on what you find
wire, switch, mounting parts, beer, etc.: varies. hopefully your basement is well stocked with leftover fiddly bits from other stuff.

All in all, you're looking at about $50. Well worth it compared to a fancy commercially produced headlight system because you can replace any part in the system for really cheap and can source parts from anywhere instead of having to put up with an insane markup from some light manufacturer.

12v 7ah SLA battery:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=6042778181
(this is the same spec battery I am using and it is just the right size to fit between my cranks and rings comfortably)

12v 5ah SLA battery:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=6042789032
(note that this battery is probably a bit too wide to fit comfortably between the rotating cranks)

I just got 2 NiCd 7.2v batteries with chargers from ebay for about $17 shipped. Serial connected the 14.4v will overdrive a MR16 nicely. I also got a pair of optronics housings for $8 shipped. Add on the connectors and switch and you have a basic system. The 1800mah NiCD should power up a 20w for 45min. A pair of 3300mah NiMh will set you back $35 and last closer to 90min. Try "rc nimh", "rc nicd", and "optronics halogen" on ebay. Batteryspace.com has bulbs, rc connectors, and a switch for decent prices. The optronics housings come with a connector built-in.
I'm using a single NiCd to overdrive my 6v 6watt helmet light.

Ebay is a good tip, there are two auctions right now for the Optronics light many commuters use, you can pick up a pair for 3 bucks + shipping. The model you want to look for is QH-12IT.