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successive switch on cause damage?

Discussion in 'Projectors, Screens & Video Processors' started by Jules, May 31, 2003.

  1. Jules

    Jules
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    I know we need to look after our projector lamps, but how far do you go.
    We were settling down for a movie (the VW11 projector had been on about 5 minutes) when I accidentally pressed the 'power off' button.

    Being the cautious guy I am, I refused to turn it back on for 30 minutes to prevent heat/power build up which I thought might damage the lamp.

    Is this unreasonable? I'm sure I read somewhere that this can cause lamp fatality. Everyone thinks I've gone mad. Have I?
     
  2. frog

    frog
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    Someone in the office told me he fitted a cheap UPS to safeguard his sony 10HT from power cuts, said those can kill a projector.

    Can't say I have ever tried to pull the plug while the projector is running...

    I have switched my HS1 off and back on a few minutes later (usually after the fans have stopped running), it has never blown the lamp.

    On a slightly different subject if I may, is better to leave the projector running even if you are not watching for a short period of time (30 minutes or so), or should it be switched off and back on later ? Same old story I guess about lamp bulbs, TVs, amps, etc...
     
  3. theritz

    theritz
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    Hi Frog,


    He's probably right - if there's a power cut there's no fan running after the bulb has gone out to cool the insides of the projector - the same goes for pulling the plug on a PJ - even if it doesn't kill the lamp outright, it won't do much for it's state of health, and the residual heat inside the PJ could damage the optics.

    Sean G.
     
  4. gothmog

    gothmog
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    Aside from a mains spike from damaging the projector (as it could any piece of eletronic equipment) I feel the whole sudden power off overheating issue is over exaggerated..

    If you cut the power to the PJ then the bulb cannot possibly get any warmer than it was the moment before power off (even with the no cooling) if it did that would be energy from nothing (there is no power to the bulb!).

    From the behaviour of my AE300 when the power has suddenly been cut (a couple of times) the danger appears to be from restarting the bulb when it is still hot from the previous power down. So if I cut the power suddenly, when the power is re-applied the projector will go through the power down full fan cycle for 5 or so minutes before coming back on.

    So yeah, if your projector doesn't sense a nasty power off then leaving it off for half an hour to cool down before re-powering is sensible. However I don't believe the sudden power-off in itself is particularly harmful...

    -- Jon
     
  5. Kramer

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    Disagree again :)

    Sudden "power off" without adequate cooling off can & has been disastrous for lamps/bulbs.

    Ever heard of "turbo timers" in performance cars? While not exactly the same as the PJ issue, still similiar cause & effect.

    Some members here (& I'll not name names ;) ) have blown bulbs by accidentally disconnecting the supply to their PJs while running.

    Hope it won't happen to you, but rest assured premature power downs/restarts are detrimental to PJ lamp/bulbs.

    Can't say you haven't been warned :)
     
  6. gothmog

    gothmog
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    But that's the point, without power how can the bulb (which is the source of the heat) get hotter?

    I am by no means recommending pulling the plug as a matter of habit ;) I just wouldn't sweat it happening on the odd occasion by accident. There is no doubt that the life of the bulb is highly related to the number of starts it goes through...

    -- Jon
     
  7. Pionir

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    >But that's the point, without power how can the bulb (which is the source of the heat) get hotter?

    Surely by the fact the bulb is hot and without an adequate delta T (no fan blowing) it means the heat isn't going away fast enough? Therefore it'll not have enough heat dissipation and get hotter and blow up?
     
  8. Kramer

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    Not about to go into the physics of it here (@ > 3am) but the lamp surface temp can increase significantly after a premature shut down.

    Trustm me guys, I know a few members who've had bulb failures after such events (& no they didn't restart their units immediately after this - gave a good half hour before powering up again).

    Might be hard to understand, but it's a fact :lesson:
     
  9. Jules

    Jules
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    Sounds like I was right to be cautious then.

    If it had only been on for say, 1 or 2 minutes, would the same apply? Are we talking about just heat problems or cumulative power used to ignite the lamp?

    Anyway I've now hidden the original remote, and re-programmed my pronto so that a 'PIN' is required before powering up or down the projector.
    I'm considering a UPS too, but I've not seen any with sufficient power to drive the projector.
     
  10. maj74

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    Come on guys...this isn't rocket science.

    With the power on, and the bulb lit, you have a heat source and fans that keep the air moving through the machine in order to prevent heat build-up.

    Now when you turn it off normally, the fans keep running. Why? because you still have a heat source! Ok, it isn't on any more but it's still damn hot and takes some while to cool down. (which the fans no doubt help with by continuing to shift air throught the machine.)

    Pull the plug and you're causing two problems. OK the bulb is never as hot as when it's on... but without the fan on it's going to take LONGER to cool down and while this is happening you have STATIONARY air inside the machine which is going to be heated by the bulb.

    Sure the temperature of the bulb drops sharply at first and slower as it cools, but it's that first minute or so after rthe plug is pulled that'll do the damage, if any is going to be done.

    I suspect, though my physics isn't fresh enough to be absolutely certain, that the stationary air makes one hell of a difference and the temperature inside a pj which has just had it's plug pulled climbs VERY fast if only for a short time.

    How damaging that could be is a question only projector electrical specialists can answer...
     
  11. Pionir

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    Hmm thinking about it again, I think Gothmog is right.

    If the bulb is at say 75°C when it's running with fans, it could be like that for 2 hours or more while watching a film and be fine.
    It'll also have a steep temperature gradient from inside to outside (say 150° on the inner surface of the glass)

    If you power it off suddenly and the fans stop, it'll slowly cool down. Ok the air in the case will heat up, but the bulb can never go over 75°C. Also the temperature gradient will be lower due to no heat source inside the bulb.

    So it's a lower temperature, with a lower temperature gradient. How can this be worse than when it's running?
     
  12. maj74

    maj74
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    Simple, when the bulb is on, the air is being MOVED by the fans. pull the plug and there's NO MOVING AIR, it gets heated quickly by the bulb which is still hot and this in turn slows down the cooling of the bulb. The surface of the bulb will probably be considerably more than 75 degrees to start with.

    In short, when you switch off normally the fans keep going. It's for a reason. I don't know HOW MUCH damage it does. As I said earlier, that's for an electrical engineer to tell us!!
     
  13. theritz

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    I hesitate to post again on this thread but cannot resist........... in case of confusion the following may assist........

    Do not turn your projector off by pulling the plug:

    This will not kill the bulb, but may shorten it's life prematurely by not controlling it's cooling down period. The absence of power to the fan will mean that residual heat from the lamp will slowly cook the optics of the projector, long term damage is inevitable.......


    IF You Pull The Plug (or someone causes the power to "trip" while the PJ is on..... Grrrrrrrrr)

    Restore power as quickly as possible to the projector and allow the fans to cool the PJ, thereby avoiding damage to optics as aforesaid........ DO NOT ATTEMPT to turn on Projector, as Lamp will not appreciate "hot start" and may promptly die before your eyes...........


    To turn off projector, press "standby" switch, and wander off for a tea/coffee/beer while your projector does its thing.


    The End.


    Sean G.
     
  14. zoolap

    zoolap
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    The UPS issue was of concern - so should you or shouldn't you use a ups?
     
  15. Chris Frost

    Chris Frost
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    Heat stresses in lamp modules

    The arc inside your projector lamp burns with a temperature close to that of the sun.

    The fans help keep the lamp running at a stable temperature by cooling it and the surrounding area.

    It is the ambient temperature of the surrounding area that rises if power is cut. This also affects "evenness" of cooling of the lamp. This is how the heat stresses are created in the lamp glass. These become points of weakness where a fracture could occur next time the lamp gets hot.

    Regards
     
  16. LTJ

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    Chris. On the issue of "ambient temperature of the surrounding area " What advice could you give to help cool any PJ?
    Cheers in advance.

    Totally OT but Chris Frost. That is such a wonderful name.
    No I am not taking the pee!
     
  17. Chris Frost

    Chris Frost
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    Err...thanks :blush: :)


    When I said surrounding area I was talking about the space inside the projector immediately around the lamp.

    Room temperature is important too. Most projectors are ceiling mounted, and as most of us know that hot air rises then this means that the projector will be sucking in warm air.

    For those lucky few building a room or with an understanding partner who are happy to have their living room rebuilt around a projection system then some sort of ventillation system is possible. A clean cool air feed from outside or an aircon system is like heaven for a projector.

    The best most of us can acheive without involving divorce lawyers is to manage the air in the room to reduce heat build up.

    This could be something as simple as a fan blowing cool air from floor level towards the ceiling, or just leaving a window open to help ventillate the room. When ever you move air like this though there is always the risk of moving dust too. It is up to you to weigh the risks and benefits.

    Regards
     
  18. LTJ

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    Chris thanks for the swift reply. You should know, being in the business. So if you could 'air condition' your room especially so during hot spells. This should alleviate to much stress on the PJ, right?

    I know the name thing was odd to comment on., but not to labour the point- it has a great resonance to it.
     
  19. Chris Frost

    Chris Frost
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    Aircon can really help, particularly with humidity which is relatively high in the UK and gets worse when we have a warm spell.

    Thanks.

    Regards
     

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