Philips 1000W US M48 Metal halide lamp lit at full Power

this was quite an achievement for me.

as due to the electrical specifications of US high power Metal halide lamps, normally to light one in the UK you need 400V 3 Phase or a very rare 240v 50Hz CWA Autotransformer ballast because the US lamps have an arc voltage of about 265V, so to be able to use a choke to run one of those you need an open circuit voltage of 400+ volts (remember the rule of thumb of, a lamps arc voltage cannot be more then half that of the OCV give or take a few 10s of volts)

but I managed to light mine by first of all taking a 400W Mercury and 600W SON choke and putting the 2 in parallel, this gave me 8-10A with an open circuit voltage of 240V (ie with no load the voltage on the output was 240v) then what I did is I fed the output from that ballast setup into the centre tap on my variac and what this did was double the voltage but half the current (because remember the chokes limit the total Power), so now I had about 4-5A at roughly 460v open circuit (theres some voltage loss here and there due to the Core of the Variac saturating) and bingo i suddenly am able to run my lamp because now I have 400+ volts OCV! and the chokes limit the current, and by tweaking the variac i can get the lamp current smack bang on 4.2A (which is what the fluke DMM in the picture is for)

this setup is also how I was able to run my 700W US Mercury lamp but with that I only used the 600W SON choke and variac, and made sure current was on spec for that lamp which was 2.8A