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Metal Halide lighting problem

Discussion in 'Electronic Design' started by amdx, Feb 3, 2009.

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  1. amdx

    amdx Guest

    Hi All,
    I have a friend that has a Tuna boat, he uses two Metal Halide lights to
    light up the deck. The boat has a 3 phase generator onboard.
    This drives a large freezer compressor and an air compressor. When one of
    the compressors comes on the lights go out, need to cool and the refire.
    The lights are single phase 240 volt units.
    What can be done to keep the lights working during compressor startup?
    Would a constant voltage transformer such as this help?|66:2|65:12|39:1|240:1318|301:1|293:1|294:50
  2. Ecnerwal

    Ecnerwal Guest

    First cover the possibility that the present wiring is done all wrong -
    ie, are the lights and other single-phase loads all piled on one phase,
    or are single-phase loads distributed across phases sensibly? Is the
    generator just plain too small and needs to be upgraded? Are there
    capacitors on the compressor motors that might be bad, or should there
    be capacitors, but there are not? Certainly for the air compressor, an
    unloader valve would be a good thing, if there is not one on it (or it's
    not working right if there is) already.
  3. amdx

    amdx Guest

    That is one of the captain's ideas.
  4. Jamie

    Jamie Guest

    Use different lights and a separate generator for them."
  5. No, probably not.

    If the compressor doesnt come on too often then how bout a UPS system? Might
    be a cheaper solution and provide enough juice to keep the lights on. The
    problem is that the compressor might suck the juice from the ups too but
    what you can do here when the compressor turns on it cuts the power to the
    ups for a few sceonds. The ups will supply current to the lights and then be
    connected back.

    If metal halides can be run with DC then simply using a power supply will
    work. Large enough caps to keep a temporary supply. In fact what you would
    want is to charge the caps before the compressor came on, disconnect ac from
    lights and connect cap then switch back. This way the cap is only on for
    charging and not wasting power(Although probably not an issue) and the
    light's are not running off dc for too long. This might be the easiest and
    cheapest solution if it worked.

    You can try other things too like batteries to an inverter but basically
    your creating a UPS system. Of course you can replace the lights or get a
    more powerful generator.
  6. Good idea, but you don't try to run the compressor off the UPS. It
    gets wired directlyh off the generator. The UPS is just for the
    lights. Assuming we're talking about something like a couple of 400W
    metal halide lights, a 1500VA UPS should be okay. Here's one for $200:

    Best regards,
    Spehro Pefhany
  7. of course ;)

    That is the problem I tried to discribe which is why you might have to
    temporarily disconnect it from the generator while the compressor is turning
    on. I suppose one would simply have to test for this or by a larger ups or
    get more of them.
  8. Guest

    so you probably figured that the voltage is dropping too much when the
    compressors kicks in and the lights can't continue through the voltage

    1) check that the lights and comps are wired to the generator with
    seperate wires, you don't want them to share any long calbes that
    would make the voltage drop worse than it is. The generator will drop
    some but extra shared wiring will make it worse..

    2) Some compressors can be started with an unloader, which is a valve
    that releases the back pressure...

    3) Add a few incandescent lights to the light system so that when the
    MH lights need to re-strike but in the meantime you have enough light
    to work with...

    A UPS for the MH lights is an obvious answer but if they are big
    lights that may be very heavy and expensive..

    good luck
  9. I would submit that a UPS that does not operate properly when the
    input voltage sags is not really a UPS.

    Best regards,
    Spehro Pefhany
  10. Well, as you well know it could only take so much. If the compressor draws
    enough juice it could cause it to sag. I guess the only way would be to test
    it out... not a big deal and not a big deal if it does need to be
    temporarily disconnected.
  11. It *is* sagging-- that's what's killing the arcs in the metal halide
    bulbs. And it's not good for them-- they should be allowed to cool
    fully before restarting.

    And the whole POINT of a UPS is to maintain quality power on the
    output if the input drops below nominal.

    Best regards,
    Spehro Pefhany
  12. Martin Brown

    Martin Brown Guest

    One possible solution not mentioned yet is to replace the MH lamps with
    ones that are capable of nominally instant restrike. They take more like
    2-3 minutes to recover from arc failure back to a useful brightness
    rather than the 10 minutes on traditional lamps and ballasts. eg.

    No idea how they would shape up in a maritime environment with salt
    spray etc. And they are obviously more expensive.
    Check the wiring. Put a simple filament lamp in parallel so you don't
    lose all lighting for an extended period?
    Probably not. A suitably rated UPS between the lamps and the generator
    might help. Presumably the power only dips for a few seconds when the
    compressor is pulling its peak maximum starting current.

    Martin Brown
  13. amdx

    amdx Guest

    The captain did mention a UPS, he has one for his computer and wondered
    one would work on the lights.
    Looks like I should make sure the wiring is configured to eliminate as
    much voltage
    drop to the lights as possible. If that doesn't help then look into a UPS,
    different lights,
    or auxiliary lights during the cooling and refire time.

    These lights have voltage taps on them like 208V, 220V, 230, 240V. I don't
    where they are set, but is there a scenario where one tap would be prefered
    to help
    keep the lights on during the brownout?
  14. Probably not-- without compromising things during normal operating

    Best regards,
    Spehro Pefhany
  15. Depends on how the ups works. If it's simply hooked up parallel to the other
    power source then it too can sag. All depends on the compliances. I'm no
    expert but I guess they just use batteries and an inverter. The batteries
    can only put out so much surge current(although I imagine it is pretty
    decent for lead acid). This still might not be enough as the compressor
    might "steal" it too. It's only a hypothetical and I pointed it out just in

  16. The problem is simply that the voltage is drooping because of the large
    surge current when the compressor comes on. Similar things happen, say, when
    peoples AC comes on and the lights dim. You gotta regulate the voltage
    somehow. I'm sure there are many ways but it all depends on how much
    regulation you need.

    Your power source, the generator, can output only so much current. The
    compressor is a load as it the lights. When the compressor comes on it
    "overloads" the generator. Basically because the compressor is "asking" for
    much more current than the generator can output the generator drops it's
    voltage to compensate(since the compressor draws less current with less

    The problem here is that when the generator drops it's voltage it it no
    longer supplies the correct voltage to the lights which they need to run.
    (which is different than the compressor which is mainly current driven)

    What this basically means is that your generator is not big enough. Get a
    bigger one or supplement it.

    Usually DC motors have a start capacitor to supply that extra juice:

    And AC motors can use a similar feature but that it works in a different
    way(offsetting the current at startup to reduce the surge)
  17. amdx

    amdx Guest

    I had another talk with the captain,
    The lights are 1000w each so the UPS suggested is to small to run one light.
    Sometimes only one light goes out, so maybe the voltage is very close to the
    point where the light would stay lit during the sag.
    The generator is a 30KW 3 phase unit.
    The freezer compressor is a 7.5hp 3 phase unit.
    Voltage normally runs at about 219 volts.
    The air compressor is not a concern (only used to power main motor starter)
    normally off.
    The 3 phase circuit breaker box has a breaker that supplies 2 phase to a
    second circuit breaker box.
    The second breaker box supplies two 1000watt lights on a single 10 gauge
    Captain said the lights have taps at 110v, 220v, 240v, and 277v.
    They are now using the 240 volt tap.
    Here is a generic schematic of a metal halide light, I found.
    I'm figuring he's running the lights at a low voltage with the 240v tap and
    a 219V supply.
    Is that correct?
    If so, I'm going to suggest adjusting to the 220v tap.
    Then try disconnecting one of the lights and running just one light on the
    single 10 gauge wire.
    Maybe the combination of the two will be enough to keep the lights lit.
  18. Ecnerwal

    Ecnerwal Guest

    Yup, if the voltage readings are accurate, that will probably do it. Try
    just that, first.
  19. 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..
  20. 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.
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