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Power off movers after loss of DMX, with delay


david.elsbury

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Another weird one...

We are installing some Chauvet Maverick MK1 spots which have a feature where they will lamp-off (actually it's an LED engine, but whatever) after they lose DMX data.

I would quite like to have them set up so that once the console (in this case a DMX USB interface) turns off and the DMX is gone, they turn off - but of course, I would like them to have the opportunity to cool down for 10 or 15min after they have lamped off.

 

So I have done some searching for time delay relay and find either very expensive power sequencers, or phase loss relays. Not sure that either are the right thing? Because a phase loss relay is designed to cut the power instantly.

 

What else could or should I search for?

 

Thanks!

David

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If they're LEDs, is there really a need for a cool-off period?

 

 

The junction temperature can be quite high, and whilst a passively cooled LED may not be affected, many fixtures (including this Chauvet device) have fans fitted and may well benefit from a cooling down period.

 

So I have done some searching for time delay relay

There are basic time delay relays available which can do power on delay or power off delay. I have certainly bought such a device for some £10 or £20 to modify an EMO mains switcher. You might even cannibalise a toilet fan time delay switch! :-)

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Would a lamp off cue for discharge and high powered led's at the end of the show be the easiest solution, so you leave an end of show audience look running while you pack up, then when you are ready to shut down the desk, you can power down the fixtures ?
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Genuine OFF delay timers exist. They must be cheap for things like toilet fans, but from RS they are NOT cheap. The other consideration would be that you would have to install one inside each lantern, which would void any warranty -not my choice on a new install.

 

I'd look for the feature to lamp off with fan on in the DMX features and try to achieve cool down that way. Maybe even have a program written to do just that. Then use a power off relay.

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I have to say that I don't think am LED fixture will need cooling down time.

 

As soon as the power is off the LED it is cooling down, even if there is active cooling with a fan there will be a heat sink attached to the LED which will be cooler than the junction temperature.

 

Also unlike Lamps there is no filament to break due to weakening at high temperatures.

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As soon as the power is off the LED it is cooling down, even if there is active cooling with a fan there will be a heat sink attached to the LED which will be cooler than the junction temperature.

This is pretty much what I was referring to. I understand that the fans are there to protect the guts of the electronics during normal use, but once power is removed, I'd say the need for air-cooling is also removed.

LED Projectors I've used (which for more traditional lamps have the standard time-delay power off of their fans) don't need a cool-down period...

 

So the question remains - is there a specific reason why you think you need to have a cool-time before losing mains?

 

 

 

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I want to be able to isolate the fixtures due to either infrequent use, or other companies using the space and waiting to make it so that they can't use them.

 

The movers will be wired via contractors (relays) so they can be isolated- no need for individual relays or timers :)

 

I was just kinda thinking that, as the fixtures are fan-cooled it would be best for them to keep the fans running for a few minutes after lamp off.

 

Will send Chauvet an email and see what they say about just cutting power :)

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I doubt it would be much of an issue to just kill the power. Certainly in my experience no one waits around leaving LED fixtures to cool deliberately. Chances are there will often be a natural delay between pulling DMX and power off anyway.

 

However, if the purpose of this was to automate power off on loss of DMX (for example when there are inexperienced operators) then perhaps an off-the-shelf solution might be a combination of a replay unit that automatically takes over on loss of DMX and a switch pack. Assuming you can find a replay unit that can automatically run timed sequences or something similar this could wait the desired amount of time (with all switch channels at full) and then send a cue with all switch channels at zero. You could also include home values. Theoretically the time delay would mean that if you had a problem, temporary loss of DMX shouldn't be an issue. The main difficulty I see with this is the startup routine and (automatically) maintaining power once the console is connected.

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Thanks all. Reply from Chauvet:

 

It would be possible to power off the fixture directly, obviously, any cautious measures taken to protect LED's and Lamps are always beneficial, but it is possible to power off the fixtures without causing any damage.

 

As these will be installed permanently, I would like them on contractors so I think I'll go ahead with the idea to do a DMX disconnect, with a delayed turn off

 

Cheers

David

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A simple 555 circuit will do the time off delay easily and for less than a couple of quid,the more complex issue is how you detect loss of the DMX signal,my first thought is a pair of opto couplers with the leds wired like the simple DMX testers and the output transistors used to fire the 555 circuit.
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I'm sure something could be hacked with a sensitive relay and a contactor, or maybe if you're after a project then an Arduino and shield would work well.

 

If you're interested we could make something that did this for you - would be a simple firmware mod to run one of our PWM dimmers as a switch opening after a period of DMX loss. I guess send me a PM if you want.

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