series globes keep blowing in dmx light.

[skinah]

I have built some DMX controlled lights myself recently which because OZ uses 240 volts as the mains I need to run two ENH 250W/120V globes in series to run them off the 240v here. The lights work excellent, the problem being that when one globe blows, the other globe also blows. I mean they do both physically blow and burn the filament out each time one decideds to go. Its like one blowing causes a power surge which blows the second globe. Has anyone had this problem before in a design? I am using a BTA16 triac to control the level/fader of the globes, other than that is a very simple series circuit with two globes.

Is there anyway to protect the globes from burning out or limit the current/voltage to each globe cheaply ? They are burning out way too fast in about 30% of their rate life and when one goes it takes the other globe out meaning 2 globes need to be replaced and its getting expensive, otherwise the lights work great.

 

[busbar]

If the first lamp fails in a shorted mode, this would stress the remaining lamp by overvoltage. A center-tapped autotransformer may reduce the overvoltage problem.

 

[skinah]

Thanks for the reply. I'll look into this but the transfer will need to be quite large and theres no room left for 2 large transformers which would be needed to do that not to mention the rise in price.

Any other ideas on limiting the current or voltage so it cant rise high enough to blow the globes ? What about using capacitors to absorb the extra voltage as it must only happen for a split second when one of the globes blows. Would the size and value of the caps need to be as large and expensive as a transformer ?

Thanks for any further ideas.