Soft Start?

"The OEM used mechanical contactor and they do not hold up well"

Use solid state relay instead.

The term "Soft Start" is a motor control device, they typically don't provide info on resistive applications because it is often done differently for that application, The same type of device for resistive loads is called an "SCR Power Controller". Different manufacturers, and there are several other design considerations regarding that. Contact people in the heating control industry.

You generally use a soft start to limit the inrush current of an inductive device such as a large motor. You have a resistive load so will not have the same issues.

Suggest you replace the contactor but instead of going for an AC1 rated device you could go for a more substantial AC3. kW rating would be the same but made for much more onerous duty cycle.

Using a soft start might help to increase to increase lamp life by limiting the current.

You will still need a contactor to bypass around the soft start after 30 secs (ish) to reduce losses.

These Quartz Halogen lamps have a large inrush current 8 to 14 times the operational current.

Yes the increase in lamp life was a noted benefit. But not because of reduced current. Lamp life increase due to reduced stress on the element.

Some of the soft starters that I was looking at had internal bypass.

OK I'm with the program now.

The "inrush" current you mentioned is due to the filament being cold when it is first turned on. The cold resistance is very low.

In studio lighting applications, where nkW lights are turning on and off with gay abandon, the lamps are never turned off completely. Some current is always passed through them even when not illuminated to keep them warm/hot so that the lamps don't pop prematurely and they can also be quickly modulated in intensity (eg flashed).

Studio lighting is normally controlled with a dimmer pack with DMX control. Easy to set up this way but if you don't need this sort of control you could emulate the preheat function with external resistors paralleled across the contacts of your control device (contactor).

When the contacts are open the current flows through the resistor in series with the lamp and when the contacts close you get full voltage across the lamp and they illuminate at full intensity.

Inefficient for sure. High power resistors required...yes. You could use ordinary lamps for the high powered resistors at a pinch.

Dimmer packs have all this functionality built in and also provide multi channel controlability. They also operate standalone without DMX. They use Triacs.

I think semiconductor control is what you need here.

What was the mode of failure for your contactors? Burnt coils or fried contacts?

Does this help?

Burnt contacts is the problem. In operation these contactor may open and close 60 times an hour. This varies depending on the size of the product. Smaller sizes are easier worked may be fed into it so frequent the lamps never go off. Large sizes may have it turning off and on 10 times an hour. Not sure contactors were design to open and close that frequently.

Download and read this.

http://www.chromalox.com/content/training-manuals/TM-PK501-SCR-power.pdf

Nice one!

Add that to the library.