Metal Halide lighting problem

Far too risky. Any glitch (not just due to the compressor) could plunge the deck into prolonged darkness at any time. He ought to consider fitting a different system altogether - or at least some sort of battery-operated emergency lighting..

Or put in a compressor that has a start-up pressure bypass.

...Jim Thompson

That won't stop a dangerous situation arising if there is the slightlest glitch in the supply from any other cause, or if someone accidentally switches the lamps off for a moment.

I've seen a similar situation in a village hall that was lit by high pressure discharge lamps. We kept the switch on one circuit taped-over in the 'off' position, so that we always had one cold lamp ready for a quick re-start.

How bout a simple device that detects if the lights are on and if they aren't simulates the manual startup process? This way if they do go off then they will come right back on? Simply detecting current flow into the lamp and using a fet to "hold the button" should work?

Then the answer is obvious - run another wire from the other phase to the other lamp. For only 10 amps apiece, you shouldn't need much more than #12, or even #14, if the run's not too long.

Also, wire the lamps for 220. ;-)

Cheers! Rich

"UPS" stands for "Uninterruptible Power Supply".

A UPS is a device that will continue to supply its specified output voltage regardless of what happens to its input. I think the most common type of UPS these days essentially consists of a battery charger, rechargeable batteries, and an inverter.

The suggestion is to have the refrigeration compressors and UPSD input connected to the generator, and have the lights on the output of the UPS. With this arrangement, nothing that happens on the generator output would affect the lights. (and if it does, the UPS is broken)

The ignition circuit operates continuously as soon as the power is restored; but the lamps won't re-strike until they have cooled and the internal gas pressure has dropped.

run the motor all the time, put an electric clutch between the motor and the compressor, actually you could put the clutch between the power source that drives the generator and the compressor

A more practical means of reducing compressor turn-on surge would be to use a soft starter. Google returns 3,740,000 hits for motor soft starter. This is an extremely common problem with a lot of possible solutions (delta-wye, reduced voltage, variable voltage and frequency inverter type), and I would be inclined to start a search for the most appropriate soft starter with a call to the refrigeration equipment manufacturer.

From your descriptions above, it seems like the lights run on inductive ballasts. These are notorious for extinguishing arcs at the slightest voltage sag and generally only work well in an environment where the voltage is well regulated and the lamps are never exposed to vibration (yes, shaking a HQI lamp strong enough will sometimes extinguish it). Both conditions are hardly to be expected on a boat, rather the contrary.

Note however that both problems are much less pronounced with lamps operated with an electronic ballast. These devices contain circuitry that essentially amounts to a regulated switchmode power supply with active PFC. Unless the voltage sags are particularly severe, the PFC should be able to maintain a reasonable internal rail voltage. Also electronic ballasts run the lamps at considerably higher operating frequencies and use a square-ish waveform thus shortening the intervals during which the lamp current goes near zero. This makes the arc more resistant to irregular supply as well as vibration.

While it is certain that some other backup lighting system (possibly with a lower total power) will still be necessary to ensure the availability of light in an emergency, your captain friend may be able to keep the metal halides as the primary system if he replaces the inductive ballasts with electronic ones.

Tim

Would it be prohibitively expensive to replace the electric compressor motor with a gas (or deisel) engine?

Good Luck! Rich