Power of inverter to drive 400W HID?

Hello everyone,
This noob needs some help here.

Got to dabble abit on a 400W HID recently.
The power supply for it is 220-240V AC.

I wish to drive it use a truck battery which is 12V DC using an inverter.
For the inverter, how much watts must it able to sustain (Especially for the initial surge) to power up the ballast and HID lamp?

Thanks!

I use 8 x 400watt metal halide lamps over my coral growing tanks. I have used many different types of ballast, IceCap electronic, PFO HQI magnetic, magnatec can type, and generic cap&transformer types. None of them have ever shown a current surge during starting or warm-up.

If you are useing an HQI type ballast to overdrive, you should get at least a 600watt inverter. For all other ballast types, a 500watt inverter should be fine.

Now, keep in mind, often the rateing posted in huge numbers on the front of the inverter is the "peak power" output rating. Often an inverter that says "750watts" on the front of it will have something in the literature that says "warning do not draw over 500watts continous usage". I belive most importantly will be how the unit is mounted to permit cooling. A 300watt inverter mounted with exellent airflow will likely live longer than a 600watt inverter sandwiched tightly under the seat of a car.

Thanks for the info liveforphysics.
Even though I must admit it did made my head spin awhile. Still new to HIDs.
I do not remember what was printed on the ballast but it was printed 400W on the Osram metal halide lamp itself.

I tried to run it using a inverter that was capable(or so they claimed) of supplying 400W continuos. But as the lamp died a few seconds later while it was on it's way to lighting up. I checked the fuse and they were fine but the unit refused to work from then on.
The inverter has a safety cutoff at 440W. I am assuming this might be the cause.
That's why I am considering should I be using a higher rating in Watt for the inverter.

Be careful of the wave form on the inverter output. Many cheap inverters have a modified sine wave output. Older ones used to use purely square wave outputs. It plays hell with switching supplies that use zero-volt switching. It also creates extra heat in inductors due to the current surges when the voltage changes with the square edges of the output.

The ballast will draw its own power too, usually around 10% of the bulb power, so add in another 40W there. JSYK.

I would go with a well cooled 600 watt inverter but most are at 120V so you would need another hopefully regulated and modified sine wave output. (@550 watts of the battery you aren't going to get much runtime and anything but a deep cycle marine type battery will be ruined)

Important is the power factor of the ballast: With a power factor close to 1, the inverter sees a clean resitive load, easy to operate.

Electronic ballasts with a power factor much less than 1 are dificult to operate with an inverter: The inverter needs more extra power to operate the ballast successfully. Also a modified sine (trapeze)- inverter may cause more problems with power factors less then 1..

Most inverters are capable of withstanding a surge of about 3-4 times the nominal power for about one second..

My Maxablaster has an 220v 130watt RMS modified sine inverter: The 125watt at powerfactor 0.98 the ballast needs doesn't give any problems.. The powersurge at startup is about 350 watts. It all works perfectly with temperatures well within specs. (invertertemp max 43 centigrade, capable of withstanding over 70 degrees centigrade)


Regards,

Ra.

Hey thanks everyone for their invaluable advice.
But one problem here....
I'm not well versed(read: total noob)in electrical engineering stuff so perhaps any reference to what was mentioned above like the power factor or modified sine, etc.
It also does not help that the inverter I purchased does not come with a manual too.

Anyway the 400W inverter was exchanged for a 800W. Trying it out tonight. Hopefully it works.