DC vs AC Ballasts - What's the Difference?

The difference between AC and DC Ballasts, and why it matters!
Very often we get asked if our XenonSupply Ballasts are AC or DC and what exactly makes them different.  To get a few things straight, XenonSupply only sells AC (Alternating Current) ballasts, period.  To give a short explanation, AC ballasts are more efficient, extend the life of an HID system up to two times that of a DC ballast and are more reliable.  Lets find out how!

So what's the difference?  
AC (Alternating Current) sends power through a circuit alternating between positive and negative voltages.  The number of times the signal alternates between positive and negative voltage in a given second is its hertz (Hz) value.  DC or Direct Current uses a constant steady positive voltage in a circuit.  An HID bulb requires power to flow from one metal electrode to another creating a spark inside your bulb.  The AC Ballast alternates the power sent to the electrodes because of its alternating current so the wear and tear on the bulbs' electrodes are even, because both sides are used for positive and negative voltage.  DC on the other hand, maintains positive voltage on one electrode throughout and wears down one electrode more than the other.  This increases the overall temperature since one side is always hotter and, due to this additional heat, erodes the electrode and the life of the bulb significantly.

Smoothed Direct Current (DC) Voltage Waveform Triangular Alternating Current (AC) Voltage Waveform

But I thought a car battery was 12v DC?

Correct, a vehicle's power is supplied from the 12 volt battery which happens to be a DC power supply.  So why bother using an AC ballast that has to convert DC power into AC and then send AC power to the HID bulb?  Simply put, AC Ballasts, due to its alternating current flow, puts less strain on the HID bulb's inner components while producing the same/better light output. AC systems also benefit from lower operating temperatures as well as better long term color accuracy due to its decrease in bulb wear and tear.  The additional cost of converting DC to AC is well worth the price as you will save from an extended bulb life as well as an increase in lighting performance.

A quick tip on price!
An important point to note with AC vs. DC ballasts is the price point.  DC ballasts are very simple to manufacture because they do not need to convert DC to AC and thus, they are cheaper to manufacturer and sell for very low prices.  The downfall to the DC ballast is that oftentimes they burn out faster and you end up spending more time and more money under the hood replacing parts.  AC components on the other hand, require a DC to AC conversion inductor coil and a voltage regulator which is more expensive to manufacture.  You will often find eBay kits for around $35 dollars that are usually low quality DC kits. High-end Digital 35W AC Ballasts cannot even be produced at that dollar value, let alone sold for anything close to that price.

 XenonSupply Premium CANBus 35W AC Digital Ballast
Generic 35W DC Analog HID Ballast


As you can see from the internal components shown in the DC vs. AC ballasts, AC ballasts use almost twice as many integrated circuits and electronic components to monitor, regulate, and power the HID system.  The additional capacitors are used to prevent flickering and smooth power output which helps stabilize a bulb and prolong its bulb life.  The internal relay prevents users from damaging the kit as they can sometimes be installed in reverse polarity shorting out the system and permanently damaging the kit.  The increased amount of Mosfet/voltage regulators allows for accurate power output which, in turn, provides optimal control over color output.  

*Green Circuit boards indicate an epoxy-glass compound used to protect the copper layer from corrosion and provides superior insulation unlike the DC ballasts' Bakelite circuit board. Bakelite is more brittle and prone to corrosion as well as cheaper to manufacture over Epoxy-Glass PCBs (Printed Circuit Boards).
*Our AC ballast units are shown prior to the standard Epoxy filling injected to stabilize components and reduce impact damage.

So now you know!
AC Ballasts are more reliable, less prone to overheating, cause less wear and tear on an HID bulb, and provide better long term color accuracy over a DC based HID system.  We can't tell you how many times customers call in asking for replacement parts on ballasts, bulbs, or both due to the short lifespan of other companies selling DC HID systems.  When you order your next HID kit (from XenonSupply of course!), make sure you select an AC based HID system (the only kind we sell), and know that you are purchasing a reliable and superior technology that will last.

Phil and XS Team

Tags: Tech Blog

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