The general purpose MH lamps will not run well on DC, as the one electrode along with the glass seals will be destroyed by electrolysis from it. You will need a HF ballast to get flicker free operation ,which replaces the magnetic ballast and the starter. The ballasts are available from most large electrical wholesalers or from Osram or Phillips directly, you just have to ask for a ballast for the particular model of lamp. Will give a flicker free output, but must be mounted quite close to the lamp and with adequate cooling to give best reliability. As a bonus it can generally restrike a hot lamp in a shorter time.