What is HID Ballasts?

High intensity discharge (HID) lighting, by definition, has high levels of electrical discharge, to create an electrical arc in the bulb, which emits light. Supplying the power to create, drive, and sustain this arc reliably is no easy feat. The device that does this is called a ballast. It is a complex circuit made up of many components to accomplish specific tasks. To sum it up, one could say that the ballast is a "power controller" in an HID system.

How It Works

HID systems use an electrical arc, which requires very high voltage to initially create, and then high voltage to maintain as well. This is why an HID bulb won't work without the ballast- it takes a lot more than 12V to create an electrical arc of light. First, power is input into the ballast. Often, ballast input wires have modules to smooth the power signal coming in, and provide extra resistance to the vehicle's circuit. These are generally known as CANBUS modules. Once there is a good, constant, smooth, reliable input power, the power goes to the primary circuit of the ballast. The main controller circuit of the ballast has two main functions: it inverts the power into an AC signal, and controls the voltage output as the bulb operates. It does this by sensing resistance in the bulb, thousands of times per second, and adjusting the output. To get things started, though, a high-voltage pulse must be transmitted to the HID bulb to initially create an electrical arc. This is accomplished with the igniter, which is a capacitor device that can quickly discharge a high amount of power. From there, the controller circuit takes over, and slowly lowers the power as the bulb warms up, and then maintains continuous operation.

Efficiency

All ballasts have an efficiency, measured as the power coming out divided by the power going in. If you send 10W to a device and it outputs 9W, it would be 90% efficient. The rest of the power is lost as heat, which is a reason ballasts might get warm during operation. No electrical device is perfectly efficient. The best automotive HID ballasts can reach efficiency levels of nearly 90%, with ASIC controllers and high-quality components. The average mid-range ballast is likely around 75-80% efficient, and your "eBay Special" Rs 1500 per kit ballast will be around 60%. The worst ballast Eufonious Electronics has measured was only 52% efficient. Yikes!

Ratings – Truth In Advertising

Most ballasts are rated at 35W, or 35 watts of power. However, this is quite misleading- most suppliers will tell you the input power rating, or how much power is going into the ballast when it's hooked up. Your 35W cheap ballast is probably drawing 35W input, not outputting 35W! A cheap, low-performance ballast will light up your HIDs just fine, but it might be only 60% efficient, meaning that your "35W" rated ballast may only be outputting 21 watts! That will result in nearly half the potential brightness! Good, quality HID ballasts provide a true 35W of output power. UGLARE slim ballasts actually output 38 watts! By just switching your ballasts to high-quality ballasts, you'll often improve the performance of your HIDs.

Individual Components in BallastsPower Input Connector

By industry standard, all ballasts use a 9006-size input wire. Your HID kit should come with an adapter to convert your socket size, such as H11, so you can plug it into the ballast connector. These connectors should be fully waterproof. The connector may also have an LED built-in, just for convenience, which comes on anytime the ballast is getting power.

CANBUS Module

On the power input wire, or built into the input connector itself, capacitors and resistors will often be used in order to smooth any fluctuating power signals coming in, like you would see on a Daytime Running Light circuit. These also provide extra resistance to the vehicle's circuit, to prevent any CANBUS systems from detecting a problem, in case the HIDs use less power than the factory bulb. Not all "CANBUS" modules are the same- some provide more resistance and smoothing than others, depending on the design.