AC vs DC HID Ballasts

A customer recently asked if SKBOWE was comparable with AC and DC HID ballasts, a confusing question because every HID ballast I’ve ever seen has been marked for 12V DC in, 85V AC out (bulb side). Turns out there actually are “DC” output HID ballasts, and they should be avoided as D2S bulbs are specified for AC drive only.

AC vs DC

As discussed on the issues page, HID bulbs are arc lamps that run a fixed current through two electrodes in a sealed quartz capsule. The voltage drop is about ~85V after ignition (20kV) and warmup. Like any arc lamp, electrons jump off the negative (-) electrode, and impact the positive (+) electrode, causing the (+) side to run hotter and wear out faster. To counter this effect, all OEM ballasts and most aftermarket designs send AC current to the electrodes, alternating each electrode between (+) and (-), so that both electrodes wear evenly.

Because the input power from the car electrical system is nominally 12V DC, there are two stages required to output the necessary power to an HID bulb:

  1. Step up 12V DC -> ~120V DC, using a boost converter with a flyback transformer, rectifier diode, and filter capacitor,
  2. Chop the 120V DC into 85V AC (RMS) using a set of push-pull MOSFETs (H-Bridge)

However, Chinese cost-cutters, in an effort to produce increasingly cheaper ballasts, figured they could get rid of the second step and feed DC directly to the bulb. The result is lower component count, but a bulb that will burn out very quickly due to rapid erosion of the positive electrode. It will also result in a lopsided, unstable arc that will “dance” and not locate at the center of the reflector foci.

Some Ebay Sellers are starting to market the difference, but price is almost always the most reliable indicator.

Some eBay sellers are starting to market the difference between AC and DC.

How to avoid DC ballasts

Price is usually a giveaway, though some manufactures have figured this out and are now up-pricing DC ballasts to make huge profits. Because DC ballasts are cheaper manufacture without the DC to AC stage they sell for very low prices, say, below $35 for a kit. AC ballasts require a large inductor and HV regulator for DC to AC conversion and are more expensive to manufacture. High-end Digital 35W AC Ballasts can’t be produced at that price, let alone sold for anything close. Without special equipment it’s hard to test at home, so make sure to order from a reputable company that specifies an AC output.

Also it doesn’t help for online shopping, but AC ballasts are significantly heavier than DC ones:

Weight of AC vs DC ballast


The what NOT TO BUY post has an example of a DC ballast. The Morimoto XB is an example of a good AC ballast. When I get some free time, I will update the ballast selection page with measurements from the ballast collection.

SKBOWE Batch 3 Ready to Ship

Of 25 units potted so far in Batch3, 12 have sold, and 13 are ready to ship! There are still two AL Gen2 bi-xenon pigtails available as well.

There are another 17 units of PCB assemblies ready for potting, but without an ETA on when they will be finished, they are being pushed to Batch4.

SKBOWE Batch 4 is ready to pot

When these are complete, I am waiting on 8 units worth of capacitors which are backorder until Mid-April, to round out all 100 SKBOWEs.  Based on average monthly sales, total remaining inventory should cover until October or November. After that, the future of the SKBOWE project is uncertain…

Batch 3 In Production

Batch 3 is on schedule for Feb 15 ship date! Building 40 sets this time, which leaves 10 sets worth of parts left in Batch 4 to experiment with different designs or for custom orders (harnesses, DRLs, etc).

Batch 3 – 80x PCBs fully assembled

Some fun stats about 40 sets of SKBOWE (80 units):

  • 320 wires cut, 640 stripped, 400 soldered
  • 400 capacitors + 240 diodes + 80 resistors = 1440 leads soldered
  • 80 heatsinks cut and bent, 80 enclosures notched, 80 covers taped
Bending the heatsinks for batch 3

After stuffing the enclosures (heat wire, form wires, tape wires, then test-fit heatsink and insulator), it’s time to mix up some potting compound.

Stuffing enclosures, prepping covers

Then each one gets a thin layer of compound, board goes back in, another layer of compound, cover gets glued and goes on, then the whole thing gets wrapped with electrical tape to compress it. Once all of them are done, into the oven for 2 hours at 165F.

Baking the first potting pour of Batch 3

I ran out of ABS cement (more on order) so for now there are 11 (so the 9 pre-orders will go out on time).

Stay tuned for more updates!

SKBOWE Batch 2 Sold Out, Batch3 open for Pre Order

Batch 2 Sold Out!

Wow! Hard to believe but all 50 of the original Batch 1 / Batch 2 SKBOWEs have sold in just 6 months. They have shipped all over the US, as well as Canada, the UK, Ireland, Germany, and Netherlands. While there were 16 units in the initial pre-order, sales have been stronger than I expected, averaging 6 units/month from August onwards.

Batch 3 / 4 open for Pre Order

It’s sad to see the bin empty, and thinking of the stories that I have heard I can’t let it stay that way – so I have decided to go ahead and order parts for another 50 SKBOWEv2. Again, some the capacitors are backordered so there will be a Batch 3 shipping in February and Batch 4 shipping some time after that. The pre-order is open now if you want to guarantee yourself a set.

It kills me to do so, but after selling the 50 Batch1/2 units with an average profit of -$3.49/each (negative three dollars) I have no choice but to raise the price for Batch 3/4 to $110 to cover the rising cost of components and unanticipated PayPal fee increases (which happened during the course of Preorder/Batch1/Batch2).

Again I apologize and hope that a small price increase is better than no SKBOWEs at all.

Looking Forward

The original SKBOWE business plan called for 100 units total, and at this time it looks like Batch 4 will be the last of SKBOWE v2. There are several ideas for features to SKBOWEv3, such as a removable harness and a DRL detector, but the design is still tentative. I guess for now, you’ll just have to wait and see!

AL Gen2 Projector Pigtails in Volvo OEM Colors

I found the connectors that AL use on their bi-xenon projector solenoid control boards (Mouser #571-2-1718346-1 and #571-965906-1-CT) and ordered a few to make pigtails that connect the high beam solenoid into the factory wiring. The OEM connector locks securely into place, and the 12″ (30cm) automotive GXL wire is designed to hold up inside of the headlight housing. Wire is color-coded to match factory wires (yellow = +12, brown = ground) to ensure correct polarity and not look out of place inside of the housing.

AL (OEM) Salvaged Projectors

Image of projector pigtails in brown and yellow wiring
Custom made Volvo OEM color AL projector bi-xenon solenoid controller PCB pigtails.

Most used (salvaged) projectors come with short (cut pigtails) of various colors or no harness at all. I have never seen a set in yellow and brown, the wire colors used in the Volvo headlight housing for the 9005 high-beam connector.

If you want to wire up a projector retrofit without using messy splitters, I am selling these for $20 shipped (Priority Mail) to the US, or $12 with your SKBOWE order (just contact me first!) anywhere. Each order comes with a pair (2x) of 12″ GXL pigtails and four (4x) 4″ black zip-ties to match the OEM internals. You will need to provide insulated butt-style (if you cut-and-splice) or 9005 female (join inside of the high-beam connector) crimps – see this post for details.

Replica Projector Pigtails

Replicas use the same connector but a different pinout: the yellow wire is on the center (pin 2) rather than on the end (pin 1). All new replica projectors come with pigtails, usually white (+12) and black (ground). These will work fine, but if you want to go for a 100% OEM look, you can order a set of these color matched pigtails and swap the pin across. It is pretty easy to swap the pin over using a jewelers screwdriver. Or let me know first and I’d be glad to do it for you.

Ballast Testing: What NOT to buy – $20 eBay Kit

This is a post about things you should NOT buy. Please DO NOT BUY things on this page.

I’ve noted that the SKBOWE will work with just about any HID kit, but when it comes to choosing a kit, there is a difference between “can” and “should”. The old adage “you get what you pay for” is very relevant, so avoid listings like this one:

eBay auction listing of what to avoid
An example of what *not* to buy for your Volvo

Of course, I couldn’t help myself in seeing how they could possibly sell an HID kit for less than a single D2S bulb, so I put in an order and the kit arrived 7 days later:

Warning Signs to look for before installing HIDs

If you observe any of these warning signs, you should not install the kit. They are easy-to-recognize:

Warning sign #1 – It was cheap. Obviously, at under $20 for 2 ballasts and 2 bulbs, this was not going to be top quality. The Kensun (Amazon) brand kits are $60, and are significantly better than this.

Warning sign #2 – It feels cheap. The first thing I noticed was the weight of the ballast – it feels like an empty case.  My postal scale says 3 Oz (85g), including the internal ignitor! Compare to the Morimoto XB35 at 10 Oz (295g). This is a DC ballast design, so even if it did work the bulbs would wear out very quickly.

Warning sign #3 – It looks cheap. Crummy sticker placed off center with no brand name, “input corrent [sic] : 10A” (this would be 135W, BTW). Back side has wood screws holding an aluminum plate onto the plastic case, didn’t bother to countersink so the heads are proud of the surface. No weather sealing whatsoever. No strain relief on the output cord (it looks like there is a nut, but it is cast and part of the case, the wire easily slides in and out).

Warning sign #4 – It’s built cheap. The internal construction of this ballast is actually scary, reminds me of the counterfeit usb chargers that routinely cause fires – but this is running at 5000 times more volts! No potting or through holes, which will shred this in an automotive environment. Integrated ignitor with no insulation. Random transformer rather than an actual boost converter. This is a disaster waiting to happen.

Guts of a super cheap HID kit.

Please do NOT use this type of kit in your Volvo (even with the SKBOWE)! When there is talk about “EMI” issues, it is these sorts of ballasts that are to blame. Any decent company producing a reputable ballast will be 100x better than this garbage.

Honestly, I am not even sure I want to hook it up to the testbench. But if the SKBOWE can run this, it really can run anything! Stay posted for an update with electrical performance.

HID Bulb Types and Identification – D1S D1R D2S D2R D3S D3R D4S D4R etc

You may have seen references to various D-Series HID (xenon) bulbs in the context of projector swaps, D1S, D1R, D2S, D2R, D3S, D3R, D4S, D4R, sometimes even D2C and D2H. So what’s the difference?

All of these bulbs have the quartz envelope and arc positioned in the same place – so any D-series projector can use any D-series bulb by bending/cutting out the indexing tabs. For example, if you buy a AL Gen2 projector from an Audi but want to use aftermarket D2S bulbs + ballasts, just bend down the key tab! Please don’t use D*S bulbs in reflector headlights as it will effectively be a high beam!
HID bulb types. Read more about them in this HIDPlanet thread. ECG is the technical name for ballast. All aftermarket ballasts are designed to use D1 and D2 bulbs only, and will not operate the other bulb types.

D-Series Naming System

D-Series bulbs are named using 3 characters, like “D1S”.

D - "Discharge"
N - 1,2,3,4 is the type
T - S is for projector, R is for reflector

To illustrate this

1. Ignitor: integrated (D1*, D3*) vs. separate external (D2*, D4*)

The D1 and D3 bulbs have an integrated ignitor (silver box) on the back of the bulb. D2 and D4 bulbs use ignitors that detach and stay with the headlight.

Igniter built-in: D1, D3
No integrated ignitor: D2, D4

2. Voltage: mercury (D1*, D2*) 85V vs. mercury-free (D3*, D4*) 42V

Mercury bulbs (D1S, D1R, D2S, D2R) run at 85V AC. Mercury Free (hg free D3S, D3R, D4S, D4R) bulbs run at 42V AC.

3. D*S is used in projector vs. D*R is used in reflector headlight with shield on envelope glass

S series bulbs (D1S, D2S, D3S, D4S) are used in projector lamps, R series bulbs (D1R, D2R, D3R, D4R) are used in reflector lamps.

Bulb Identification

What if you are given D1R and D3R or D2S and D4S without label? You can’t see if there is mercury inside (and thus the voltage). It is possible to differentiate using the notches on the bulb.

Location of notches on D-Series bulbs
This diagram shows the notches on the bulb base, looking at the bulb, as well as the location of the notch on the lamp holder (in red)

Aftermarket Bulbs

Again, all of these bulbs have the arc in the same place, so to reduce the number of different models to produce aftermarket manufactures have developed the D*C type, which universally fits multiple notches. For D1/D3, a removable ignitor adapter is available.

5 notches? What is going on?? These are “Type-C” bulbs
4 and 5 notch D-Series bulbs are type “C”

Aftermarket manufactures don’t want to make a lot of different models. D2C that can replace both D2R and D2S. D4C for D2S, D2R, D4S, D4R and D2C. D1S with 5 notches won’t be hard to understand.

D2C replaces D1S and D2S, D4C replaces D3S and D4S

All of this makes it simpler for production, but much more complicated for consumers… And most sellers even don’t know about the real reason or the difference.

C-type bulbs with integrated ignitors can be differentiated by the keying on the ignitor connector

Another way to differentiate D1S vs D3S is based on the keying in the ignitor connector.

Finally, the last aftermarket type is sometimes called “D2H” which includes AMP connectors for aftermarket ballasts. It is always 85V / Mercury.

Aftermarket bulbs (used when the OEM ballast fails, or for projector swaps) with AMP connectors are sometimes called “D2H”, and have enough notches to fit anything.

Many thanks to this post, and the HID planet thread.

AL Gen2 Projector “de-key” Modification

You can easily modify AL Gen 2 projectors to fit any of the D base bulbs by bending the key tab out of the way (aka dekey the projector):

This is the key tab that prevents using a D2S bulb in a D4S or D8S projector
Key tab partially bent on an AL gen2 projector
Finishing the bend, using pliers to curl it completely out of the way
When complete, the back should look like this.

How to: “factory” wire bi-xenon solenoid

I had previously written up how to create a bi-xenon high-beam adapter using a 9005 extension. If you don’t mind modifying your headlights permanently, and have long enough wires on the solenoid pigtail (8~10″), with a little work you can mimmic the “factory” solenoid wiring found in the OEM AL bi-xenon headlights that use “Gen 2” (2-wire) (aka “E46”) projectors. This will also work for replica projectors, but not 3-wire “Gen 1” projectors – those require a solenoid controller.

You will need: 9005/9006 female crimp terminals, a molex crimp tool, a wire stripper/crimper, a paper clip, and some zip-ties.


First start by removing the terminals from the OEM 9005 high beam connector, by inserting a paperclip to depress the retaining tab as shown below.

Removing a terminal from the connector housing.

Next cut off the OEM terminal, re-strip the wires, and include the pigtail wire:

In addition to the two original brown wires, I’ve added a third black wire that runs to the solenoid ground, shown here inserted correctly into the terminal prior to crimping.

Using a molex-type crimper, ensure that the terminal is securely fastened to the three wires.

Crimping in progress, showing the correct length of stripped conductor and insulation position.
The new ground terminal after being crimped. The same process is repeated on the supply (yellow, +12) side.

The same process is repeated on the other wire (yellow, +12v). Finally, insert the new terminals into the housing

Insert the new terminals into the OEM housing. Retaining tab faces center.

Finally, zip tie the new wires along the harness, and plug it in…

Ziptie everything in place, and it looks totally stock!

This not only looks nicer, but also frees up some much-needed space inside of the housing.