Well, every CFL is a little different, but these steps cover the basics for packs at or above 48V; I've written them for two ways of doing it, as a generic instruction set that will *guide* most people familiar with ebikes and wiring to be able to do this.
The first thing you have to do is see if your CFL will actually run on your pack voltage, and for that you need to touch one pack lead to the screwbase of the CFL, and one to the tip of the base, and MAKE ABSOLUTELY SURE YOU DON"T TOUCH THEM TOGETHER!
Probably your pack wires are not exposed enough to do this (unlike mine, because I'm lazy and don't care until something bad happens
) So you'll have to make some wires that will let you do this, plugged into the pack wiring. That part is up to you, as I won't know what kind of wiring you have.
If this sounds intimidating, stop here, because you'll have to work directly with your pack voltage and risk an accidental short that could DESTROY THINGS if you make a mistake, in order to do this CFL connection the way I describe it, and since connectors vary by bike, I can't describe how to put them on or even which to use.
But, once you have tested it, and finally finished lighting it up, turning it off, lighting it up, turning it off, etc, and been told to stop bugging your roommates about how cool it is that this AC-powered light is running on BATTERIES on your BIKE, then you can go on to the next steps.
You'll need to know how to do basic soldering, cutting, wire stripping, etc. Possibly how to crimp connectors and have those tools, if that's the style yours are. You'll also need to know at least a little about wiring stuff up, as your parts will be different from mine and may not have exactly the same connections.
Tools and parts required:
*Wide flatblade screwdriver or other thin strong prybar with wide end
Electrical tape and/or heatshrink
Soldering iron and solder
Well-insulated thin wire (16 to 14 gauge is probably fine, it's not going to carry much current but it's high voltage)
Connectors to "Y" into your pack at the breaker or switch (controller side)
CFL bulb; 60W equivalent (15W actual draw) is probably enough
Reflector and mount of your choice (doesn't *have* to be re-used fast food cups and duct tape)
Needlenose pliers (with wire cutters built in, or separate cutters)
Inline fuseholder and small fast blow fuse suitable for your CFL's power draw (you can skip this if you're brave, or stupid like me)
Switch to turn light on and off.
* these steps and tools are only needed for systems that need the extra 1.5V or so that bypassing the bridge and whatnot will net you; it is probably easier to find a CFL that will start at your pack voltage even down at LVC.
If like me you don't *have* any others and can't buy stuff just to test out, well, do these steps. They may help.
Safety step (I don't think anyone here would do this, but still): Make sure the CFL is unscrewed from any socket it was in. You don't want to be doing this while it's plugged in and operating, or this will apply:
No, I'm not kidding.
these steps and tools are only needed for systems that need the extra 1.5V wrote:
Hold the hacksaw in place upside down over your trash can, and line up the groove in the CFL's base where the two halves split with the blade, then carefully rub it back and forth a few times until it has cut just enough into the base to see a little inside it. Be very careful not to cut too far or you may rip the CFL bulb wires out of either the bulb or the board. You might be able to fix that, but only with experience. Otherwise, go get another and try again.
Carefully insert your pry tool into this slot, and twist it gently ONLY against the edges of the plastic base. Part of the base just inside the cut, towards the screwbase, will break; that's ok. Once it is lifted open enough to "click" the holding tabs out of their slots on one side, the whole thing will fairly easily come open, so don't pull hard; you'll break things or rip wires loose.
There's not much wire length in there. You don't have to cut anything unless you simply can't reach the electrolytic cap to solder the wires to it's leads. That's the one that looks like a can, held off the board by (probably) two inch-long wires with loose insulation on them. The one sticking way out in the top pic of the thread.
Measure the distance, including all routing around things you're going to do, plus flex distance if you're mounting this on something that has to move (like the handlebars) from where this headlight will go to your planned interconnect to the pack voltage, and cut two wires with at least a couple of inches more than that. Several more inches if you're not sure. YOu can always shorten them, but lengthening them is harder.
Strip one end of each of the two wires about 1/4".
Wrap one around each lead wire of the capacitor. You'll probably have to use the needlenose for this, and also your fingernail to hold the insulation away from the wire where you're wrapping this.
Solder each of those connections.
Separate the wire that goes to the "-" lead of the cap (usually the one with a black band on the wrapper of the can), and tie a small knot in the other end of it, about two inches down. NOT = NEGATIVE, so easy to remember.
Now tie a knot in *both* wires *together* about an inch from the end you soldered. This knot will help relieve strain if you pull on the wires protruding from the case, so they won't break at the cap..
Route those two wires over the lip of the base where the piece broke off, then wrap them at that spot with one layer electrical tape. This will help keep the sharp edges of the plastic from cutting the insulation.
Hold them in place and snap the base back together.
IF you are NOT doing the above steps, then you can simply strip those wires as described, then:
Tin the ends you stripped.
Tin a small area of the screw base (the tip is already tinned).
Solder one wire to each of those two spots. Doesn't matter which is which, it's polarity neutral this way.
At this point, the rest of it is the same.
Use electrical tape or heatshrink to secure the wires to the base of the bulb and to completely cover the screw base of the bulb so no exposed metal exists, but don't cover up any vents it might have.
Wire in the switch into either of the wires from the CFL, in whatever position along the wire make sense in your setup.
Wire in the fuse holder between the pack and the switch.
Insert a fuse in the fuse holder (this is a step not always done, and people wonder why it doesn't work.
Solder or crimp the appropriate connectors to each of the two wire ends you have, so that they will plug into your pack in the "Y" fashion with the ones that go to your controller.
After you've doublechecked the wiring, then connect everything up, and turn it on.
If you used the first set of steps, you also need to verify polarity, as you'll probably blow up the CFL's board if you have it backwards. If you soldered directly to the outside metal base points, polarity doesn't matter.
If it is all working, then you can proceed to put it in whatever reflector you have or have made for it, and mount it on the bike.
I have probably left out a lot of little details. If there is something major I missed or simply am wrong about, please point it out so I can repost a corrected version. I'm going to post it as a blog post, too, once it's verified ok.
I will add the part for packs *less* than 48V nominal later, because I'm dozing off at the keybaord and having trouble thinking.