250W metal halide lamp ballast capacitor

[Sceadwian]

I've got a salvaged ballast cap from a 250W metal halide lamp, wonder what I could repurpose it for. Anyone know the internal construction of these? I'll be picking up two more tomorrow so I may just sacrifice one just for curiosity. Would they be useful at any modest DC voltage for pulse currents? I haven't tried to find a datasheet for it yet but I'm guessing they won't have detailed derating info for DC or pulse currents.

[David Hess]

It is an oil filled metalized plastic film capacitor.  The plastic film is probably polypropylene.

[SeanB]

They are reasonable for pulse operation, just will have a somewhat high ESR ( as part of the design, they are after all a wound coil of film with aluminium coating) and with the internal discharge resistor they will not hold charge for long. Great as power factor4 correction asa they do not shock you on unplugging, and will remove a lot of harmonics off the mains as well.