ok now that i understand the whole housing situation you can help me better understand the power talk. i want to know exactly what im getting into before i start ripping parts out and trying to shove new ones in. the kit im looking to get is a 35 watt or 55 watt kit. you mentioned the watts and volts and im kinda confused now. if you could help me better understand how the hid conversion is set up i would appreciate it. it seems that you are more partial to the halogen bulb replacement but i tried that on the car i had before my jeep and it never worked out for me so im gunna try out the hid kit to see how well they work.
so if you know how could you please try to explain to me how hid kits work and how they are set up?
thanks
-Ian
Bear with me - I may screw up a couple of details here, and I hope someone will correct me if I do (else I won't learn anything either!)
Old "sealed beam" headlamps are just regular incandescent bulbs, kinda like in your room lamp. The use a tungsten filament that gets heated up to the point of incandescense (therefore "incandescent,") which is why the bulb gets so hot. Higher watt ratings mean more current flows through the filament to heat it up, which means more light (and more heat!)
Newer "halogen" lamps are simply incandescent bulbs that, instead of having a vacuum drawn in the envelope, are first evacuated of air and then filled with a halogen gas at low pressure. The halogen is effectively inert, but it allows for the particles that are blown off of the filament to be redeposited - this both gives a purer white light and helps the filament last longer.
Just for the sake of completeness, let's not forget the "noble" lamps - these are tungsten-filament bulbs that are evaucated and filled with a noble (chemically inert) gas, typically xenon. You don't often find these in automotive applications, but they are relatively common in the high-performance flashlight world (like SureFire and Streamlight. My G2Z has a xenon bulb, and I've been using the same bulb for the last six or seven years. Excellent light, and damned good service life!)
NB: All of the previous use a tungsten filament that gets heated enough to begin producing light as a byproduct; cf. "incandescence."
HID - or "High Intensity Discharge" lamps are, as I recall, tiny arc lights. They don't have filaments in them - they have a couple of small electrodes with an "air gap" in between the points, and an electric arc produces the light. It is actually possible to have an illuminating arc that requires
less current (from the source) than a filament does - but it requires a
much higher voltage than the normal 12VDC. I think they run up around 20-25kV, but don't hold me to it. That's what the "ballast" for the HID lamp does - it's an oscillator that feeds a step-up transformer (transformers
cannot work when fed DC voltage, since they depend on variable magnetic fields to function!) to kick the 12VDC up to around 20,000VAC or so. This is then fed to the arc to light it off.
Just to even things out, let's say that you get an HID kit that requires 24kV for the arc. This 24kV will be provided by the ballast, and this is made from the nominal 12VDC, and we'll figure a 36W draw for the ballast (none of these values are strictly accurate - merely illustrative.) Recall from your basic electronics class - if you took one - that all values in a closed electrical circuit are mathematically related. If you require a refresher - or want to see it for the first time - go to Wiki and look up Ohm's Law and Watt's Law. I'll wait.
Make more sense now? Here comes the math (I'll try to keep it simple.)
Amperes = Watts/Volts. We're working with a closed system at this point, although it's fed by the alternator. Again, we're simplifying here. Thus:
36W/12V = 3A.
So, we will have three amperes running through the ballast. Three amperes feed the arc in the HID lamp assembly. But, we've kicked it up by a few orders of magnitude - 24,000/12 = 2,000. Current of the actual arc (theoretically) can therefore be found one of two ways:
36W/24,000V = 0.0015A
3A/2,000 (voltage multiplication factor) = 0.0015A
As I've told my tutees, "Highway 1, I-5, and US 101 will all get you to LA - as long as you follow the rules." Anyhow, this shows how little current is needed to feed a simple illuminating arc (you need much more current for welding simply because you are
melting metal - and the higher current makes for a much more energetic arc. It's not so much the visible light that will damage your retina - the UVA and UVB generated by the arc will get to your eyes much more quickly. The UVA and UVB are also what causes the "welder's tan" at the neckline and between the gauntlet and sleeve, for short-sleeve welders.
Let's compare the 0.0015A (yes - that's 1.5 milliamperes, or one and one-half
thousandths of an ampere!) that lights up the arc to what you get for the halogen - assuming an OEM dip beam:
55W/12V ~=4.583A - or about four and seven-twelfths of an ampere. (NB: In both cases - arc lamp and halogen/tungsten filament - the current given is
per bulb.)
The problem is that HID depends on high
voltage to make the arc happen, which is why you can't get by without a ballast. If you lose a ballast, you lose a lamp until you can get a new one - are you willing to carry a spare ballast?
The filament bulb may require more current, but it's at the system-standard 12VDC. And, a single spare bulb is
much smaller than a single spare ballast (I think HID ballasts are about the size of two packs of smokes, by now.)
I just happen to like using a conventional filament bulb because I am, as I said before, big on standard parts you can get anywhere. I can walk into any parts house in America and grab a regular 55W/65W H4 halogen bulb without any trouble at all - and I've got a spare pair of bulbs in with my spare fuses and relays anyhow (and spare IP bulbs. And ...)
This is also why I settled on using the ANL-format fuse with my fuse kits, instead of getting the industry-standard MEGA fuse or using the AGU high-current fuse. The ANL can be had at autosound shops, which are easier to find than industrial electric shops (although you can usually find them cheaper from me!) And, the AGU is a glass tube (like an oversized AGC,) and I didn't think it would be rugged enough to survive use in the environments we find ourselves in. Ergo, ANL (all of my kits now come with two fuses anyhow.)
If I add accessories to my truck, I use ATO/ATC fuses (just like the vehicle itself uses) and DIN relays (ditto.) I buy both in bulk anyhow - although I had to start keeping MINI fuses around (that Suzuki I got for my wife is a decent car, but it's screwing up my logistics! Something else odd - inline six, about 150ci displacement.
Seven-quart oil sump! Wha?!? The 242ci I6 in my truck only takes six quarts! At least with converting to synthetic that seven quarts is giving me 15-18kmiles service now. I may have to add a bypass microfilter, since that would allow me to run oil even longer!) I use standard Delphi Weatherpack connectors (just like you find in the trucks wiring already,) and I'll wrap the wiring up with convolute tubing - I like my added stuff to look like the factory put it there whenever I can, and I want to be able to use spare parts already on hand!
Now, if I can find an HID kit that uses standard H4-form bulbs, I may install it. Then, I'd just leave the wiring for the halogens in place and pull the relays - stow it all in the spares box. That way, if I lose a ballast, I'm not out a lamp.
You might also see "colour temperature" as a specification when looking at HID kits - for more information on that, look up "black body emitter." It's not the easiest thing in the world to explain, and I know
I'd screw it up right now.
For emissions, they're measured two ways - either candlepower (typically cp) and lumens (typically l - lower-case letter "L".) Difference between the two? Picture a pile of sand on a table - just a little one. The height of the pile is the measurement.
- Candlepower would be the height of the very highest grain of sand in the pile.
- Lumens - luminous flux - is a weighted measurement of the
entire pile of sand.
Measurements in lumens are a more accurate comparison of light intensity - "brightness" - than candlepower. You probably won't see this very often with headlamps and suchlike; but it's possible, so you should have some idea what they're talking about.
The Wiki articles on these subjects seem to be fairly free of apocrypha. I don't consider Wiki a truly authoritative source - it's more of a "jumping-off point" for directing deeper research - but most of the basic scientific articles are useful as a quick-reference. If you want deeper information, I would suggest Engineer's Edge instead (Google them.)
vendors like DPG Offroad. 
