100W HID Ballast Question

I am in the process of upgrading my 35W HID, and I have researched 100W HID kits. In working out a suitable battery, I looked at the current rating for the ballasts. Most 100W ballasts on aliexpress state that the current consumption is 5A. This puzzles me, as I understand that Volts x Amps = Watts.

So, 12v x 5A = 60W. The efficiency is less than 100%, so the HID bulb should get even less than 60W. Apart from the obvious (incorrect specs), what am I missing here??

I've tested a few 100 Watt ballasts and claimed 100 Watt ballasts with some excellent quality meters. I typically use 13.2V input to somewhat mimic a 12V vehicle electrical system with the engine on and idling with no load and batteries that are fully or near full charged. Here's an example of what I observed: Input - 13.2V x 6.53A = 86.19 Watts. Output - 94.2V x .836A = 78.75 Watts. A real 100 Watt (input) ballast would draw 7.58 Amps at 13.2 Volts or 7.9 Amps at 12.6V. Obviously, this is once the starting and boost circuits have completed their job. And the qualifier - Since the output is AC, these readings do not account for Power Factor losses so the numbers are not truly scientific results but are close enough for my purposes.

I've got one hot ballast that produces quite a bit of power but also gets very hot. Input: 13.2 x 11.69 = 154.30. Output: 102.9 x 1.144 = 117.71. The other issue is that "100 Watt" bulbs last a few hours.

BVH said:

I've got one hot ballast that produces quite a bit of power but also gets very hot. Input: 13.2 x 11.69 = 154.30. Output: 102.9 x 1.144 = 117.71. The other issue is that "100 Watt" bulbs last a few hours.

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Hi BVH, can you further explain this? Though the Chinese bulbs are pretty cheap and I don't use these powerful modded lights outside of "hobby use", its still good to know.

The highest rated bulbs I have are 100 Watts. 117 Watts to them is just too much for them to handle. They get so hot that the round arc chamber begins to melt and deform. Maybe due to refraction (?), the emitted light has a strong pink hue to it.

BVH said:

A real 100 Watt (input) ballast would draw 7.58 Amps at 13.2 Volts or 7.9 Amps at 12.6V.

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Thank you BVH. It looks like the specs provided by manufacturers are wrong. The ballast either drains 7+A or does not produce 100W. I just thought there might have been some other convention in rating output, like the 100W HID being as bright as a 100W halogen...but that didn't add up either.

Manufacturers are usually all over the map when it comes to rating their ballasts. Some are right-on, many are not even close. The only unknown variable in my testing is something called Power Factor correction. I'm not an electrician but as I understand it, with AC output, one cannot simply multiple Volts X's Amps to arrive at TRUE Watts. Frequency, Sinewave form and P.F. must be added to the equation and the Volts X's Amps calculation must be done many thousands of times per second to arrive at an average. As I further understand it, the simple Volts X's Amps calc is most likely good enough for our purposes here on CPF. So I will probably not spend the $2,000 to get a Fluke 125 Scope meter or other power meter that actually gives TRUE Watts.