Can I turn MH on right after shutting it down?

[Tiarb]

Hi!

I am getting my first MH lamp in mail tomorrow, and the dude who sold it to me told me that I should not turn it on right after turning it off. Well, I did not ask how long I should wait before turning it on again and such, so could some one here who knows about the stuff illuminate this subject a bit?

How long do I have to let the MH lamp cool down before I can safely turn it on again? What will happen if I turn it on too quickly?

Regards
HB

[Tiarb]

Yea yea I know, really n00b thingie but yes, I am going to answer my own post. I did not find the answer on this forum but I found it elsewhere, thus putting the answer here being somewhat rational... Here goes:

"When MH bulbs are turned off they should be left to cool for 20 minutes before re-starting. Turning a Metal Halide bulb on when it is already hot severely shortens the life of the bulb and it can affect the intensity of the light.

High Pressure Sodium bulbs can be restarted after only 2 or 3 minutes after being turned off."

Regards
HB

[verbose mustafa]

I always said screw it with my OHP that was metal halide. I personally waited a good 5 minutes if i was in a rush. If i flicked the power off and back on real quick I would get a weird half lit bulb and a screeching sound. Not too god for the bulb or my ears.

[corryn00]

You SHOULD wait approximately 15 mins before re-arcing the bulb. REMEMBER to keep the cooling fan on before you light the bulb and 15-20 mins after you shut it down to extend its life.

Gordon

[Tiarb]

Originally posted by corryn00
You SHOULD wait approximately 15 mins before re-arcing the bulb. REMEMBER to keep the cooling fan on before you light the bulb and 15-20 mins after you shut it down to extend its life.

Um.... that's weird, there was stated somewhere in this forum that you should let the MH cool down on its own, not with fans, because it might cool down too fast and crack or something (I think it was in that permanent thread about theories). As commercial projectors do cool the lamp with fans after shutdown I found that statement strange.

Ok, I will get a separate switch for the lamp so I can shut it down before I shut rest of the projector.

Regards
HB

[djQUAN]

a little idea: you could keep one switch for the lamp and a delay circuit linked to it for the fan so that the fan will stay on for a few minutes after the lamp has been turned off.

[nervra]

Hey djQUAN, I would love to incorporate a delay circuit into my projector, which is still a work in progress. But i have very little experience with electonics, so can you help me out?

[ace3000_1]

As commercial projectors do cool the lamp with fans after shutdown I found that statement strange.

Hmm ive had a few commercial projectors and none have had the fan running on after turn off on metal halide bulbs.

From what ive read and been told from various lighting sources, turning a lamp on when its not properly cooled down actually burns out the ignightor more then damages the bulb, as the ignightor holds the 5kv charge for longer then its suposed to because the bulb isnt ignighting.

Inside the bulb is a thermoelectrical switch with stops the bulb from ignighting when hot to save the bulb from damage and explosion.

15 - 20mins is the normal time for a re-arc in metal halide bulbs, though the bigger the arc, the longer that time becomes. Also you can buy mh bulbs that have a hot strike feature wich dont require the bulb to cool down before restrike.

Trev

[ace3000_1]

Hey djQUAN, I would love to incorporate a delay circuit into my projector, which is still a work in progress. But i have very little experience with electonics, so can you help me out?

A simple 555 timer circut and a relay with a few micro switches and your set.

Trev

[lazyfly]

Also, if the MH doesn't appear physically damaged from hot switching doing so will still generally cause the colour spectrum to shift faster than when in normal use. This as you can imagine severely limits its photosynthesis abilities with corals

Ahhh irrelevent, but I'm frustrated no one has helped me with my dali driver replacement Q in the loudspeaker forum. Sorry

p.s the spectrum shift is true, though!