This probably sounds like an extremely stupid idea, but i saw this post where someone lit a 750W SBMV on a 250W MV ballast and it got me thinking: is this kind of thing normally possible and what are the effects of it?

This probably sounds like an extremely stupid idea, but i saw this post where someone lit a 750W SBMV on a 250W MV ballast and it got me thinking: is this kind of thing normally possible and what are the effects of it?

I think the lamp might be okay, but the ballast's impedance would reduce current on the arc tube and underdrive it if the ballast was a series choke or HX autotransformer ballast.

With European SBMV nothing except the underdriving.
With the US the problem could be the ballast causing overvoltage so overheat of the lamp components in case the lamp is designed for lower current than the ballast feeds. The reason is the mercury ballast OCV is more than double of what the lamps are designed for, so there is nothing else to prevent the overvoltage than the ballast delivering less current than the lamp is designed for.

With European SBMV nothing except the underdriving.
With the US the problem could be the ballast causing overvoltage so overheat of the lamp components in case the lamp is designed for lower current than the ballast feeds. The reason is the mercury ballast OCV is more than double of what the lamps are designed for, so there is nothing else to prevent the overvoltage than the ballast delivering less current than the lamp is designed for.

My plan was to use a 400W metal halide ballast (which i use for all my H33 mercury bulbs without issues) for 750 and 1250 watt SBMVs, both of which are 220v. I don’t know if this changes anything, but I’m just making sure.

With European SBMV nothing except the underdriving.
With the US the problem could be the ballast causing overvoltage so overheat of the lamp components in case the lamp is designed for lower current than the ballast feeds. The reason is the mercury ballast OCV is more than double of what the lamps are designed for, so there is nothing else to prevent the overvoltage than the ballast delivering less current than the lamp is designed for.

Your statement abot the ballast OCV being double of that of the lamp's rted voltage only applies to 110-127v self ballasted mercury vapor lamps, but in his case, he has some examples of 220-240v self ballasted mercury vapor lamps designed for the North American market.

If the ballast OCV is at or below the SBMV voltage rating, there is, of course, no overdriving issue.
Obviously the ignitor has to be disabled (if present) when running SBMV.

Would this also work with a probe start metal halide ballast? I know they have higher OCV than mercury ballasts

Would this also work with a probe start metal halide ballast? I know they have higher OCV than mercury ballasts

The lamp's filament will burn out faster since the OCV of those ballasts is significantly higher than the mains voltage rating of those lamps.

That case I also encountered already about two years ago on a private street lighting in our town. There have been accidentally put a SBMV 100W EYE lamp on a choke and ignitor ballast which was meant for HPS 70W. The result is that the SBMV lamp did light but very dim and the colour was rather wärmwhite. As I remember this lamp for worked years in this manner until the owner called me and asked for proper maintenance.

The lamp I posted here in the gallery but it haven’t been really noticed by members except of one.