Strange problem with 1000 watt metal halide bulb.

[Baked_Bean]

Hi everybody, I was wondering if any of you had any ideas on whats going on with my setup.

For a uni project I needed to have a really bright light source, so did a little research, decided to get a metal halide bulb. bought all the parts (ballast, capacitor, mogul base, 1000w bulb, correct wires)

wired it all up, plugged it into an extension cable, and took it into the middle of the garden (in case something happened) turned it on, and voila it worked fine. So over the next few days I did some experimenting with the light (long exposures in dark areas, shadow stuff, projection. etc)

BUT i always used the same extension cable when i was doing this

Today I tried plugging it into the mains w/o the extension cable, it lit up, then died all within the space of 5 seconds - i checked and sure enough the fuse had blown. (it was a 13 amp fuse, and the ballast is only supposed to draw 8.5)

anyway, after much experimenting and many blown fuses later, ive found out the only way to get the light to work is to first plug it into the extension cable?! any other combination and the fuses blows.

So, im stuck tbh. the only thing i can think of is that the extension cable is acting as some sort of current time delay? and perhaps the ballast is drawing more than 13 amps on initial startup of the bulb.

here is a pic of the setup i have cobbled together.


any help would be very much appreciated.

[Tim]

How long is your extension cable?  Perhaps the cable is acting more like a resistor...

[Baked_Bean]

its 50 meters long, so could easily be acting as a resistor.

if it is, does that mean ive wired up the circuit incorrectly?

[adam2]

If the lamp lit correctly, then I doubt that you have wired it wrongly.
Metal halide lamp circuits consume a great deal more than the rated current when starting, and this can easily blow fuses that are apparently correctly sized.
Use of a long extension lead will slightly reduce the running current, and very substantialy reduce the starting or inrush current.

To use the lamp without the long lead, try some different makes of 13 amp fuse, some are more sensitive than others.

Alternatively, can you have an electrician install a 16 amp socket on its own circuit ?
A 16 amp "C" type MCB should easily take the inrush current of a metal halide lamp.

Another option is to insert a resistance in series with the supply during starting in order to limit the inrush current, and to by pass this resistance after a few seconds. This is not complex, but does require competance and experience with mains voltages in order to ensure that it is safe.