Parallel ballasts?

[dnsey]

I've replaced the faulty electronic ballast in an old commercial projector with a magnetic ballast. The PJ uses a 575W MH lamp, which works fine on the 400W ballast.
Does anyone know if it would be OK to run a 150W ballast in parallel with the 400, in order to obtain more light output? I'd leave the igniter connected to just the 400, as the lamp starts fine as it is.
I know that some commercial lighting installations do use parallel ballasts, but they are usually of equal rating. I only have one lamp at present (hoping to get another soon, though) so I don't want to risk damaging it by uninformed experimenting.

[dnsey]

Anyone?

[v1d9uy]

no clue sorry

[superdaveumo]

Theoretically it's possible. But, ensuring that all the components are set up properly and that they can handle all the current, I'm guessing, would be a nightmare.

[eight_heads]

i would not suggest trying it.... they're not made to be run like that and probuably couldn't handle the extra wattage

[pinkmouse]

They won't share the load properly, one will likely hog all the current and go bang...

[dnsey]

Thanks for the replies.
There are diagrams in my rather ancient Philips lighting handbook showing discharge lamps running on paralleled standard 'half the wattage' ballasts, so presumably there's no problem with current sharing that way.
My thinking is that as the igniter will be run from the 400W ballast, the lamp can only strike by drawing current through that ballast. The 150W one will supply the additional current to allow it to run at (nearly) full power. Since, as far as I understand it, the lamp is virtually a short circuit once the arc is struck, the current through each ballast is limited by the impedence of the ballast itself, so the ballast can't be damaged by overcurrent.
Please point out the flaws in my arguement

[eight_heads]

well, give it a shot, be careful, and if you don't die and a ball of fire, post your results with some before and after pics :P

[Guy Grotke]

With identical ballasts, their phase characteristics would match. With different ballasts, they may not. That might not matter, in terms of over-working one ballast or the other. But it might send the lamp a novel waveform.

On the other hand, electronic ballasts don't try to mimic magnetic ballast waveforms at all. They just use square waves and integrate to get the average power per cycle. So a novel waveform should not matter much.

Maybe the non-ignitor-connected ballast will prevent the lamp from starting by swallowing the high voltage pulse? You might have to start it with the 400 Watt ballast, and then switch in the 150 Watt.

Let us know.