Restart delay switch?

[drbob]

Hello,

I'm installing a socket in my living room ceiling for a projector, I'd also like to install a wall switch to turn off the projector when not in use (rather than leave it in standby the whole time). Projectors need at least 5 minutes to cool down before being switched back on after switch off, I'd like a switch that will enforce this delay. I've been unable to find any such "restart delay" switch from rs components, maplin or farnell.

The closest thing I've found is this industrial relay, which I guess I could use with a standard wall switch, but it's probably expensive and will take much more effort to install:

such a relay my only option or is there a cheaper domestic option which does the same thing?

Thanks in advance for any help or advice.

[Christian McArdle]

You can get DIN rail units for timing communal stair areas. These are usually used with momentary switches to give several minutes delay. However, I wouldn't be surprised if they could be used with a latching switch. You'd need to check that the delay starts from when the switch is released, not upon initial press. The DIN rail unit could be mounted in a small enclosure next to the projector.

An example is the MK 5650S.

is designed mainly for resistive lighting loads and extractor fans. However, a projector is largely a resistive load for the bulb and a fan motor, so I reckon it would probably be OK, provided it doesn't switch off 5 minutes after you turn it on, rather than off.

Christian.

[Andrew Gabriel]

Seems like the projector should include such protection internally if it's required. I assume the issue is with the circuitry not being able to hot-restrike the lamp, which typically requires some 10 times the cold strike voltage.

In this case perhaps something based on preventing switchon whilst it's still hot might be more appropriate than a timer? This could be done with a slight modification to a fail-safe relay, whereby a thermostat was added in series with the energize circuit.

[Dave Plowman (News)]

Very easy to build using bits from Maplin, etc. Based around a 555 timer.

I'd estimate < 25 quid for a 10 amp load one.

To make things even easier, they do a kit designed for the purpose.

VF 08 at 14.99 plus the cost of a suitable power supply.

[Dave Liquorice]

I doubt you'll find a normal type switch do that but

There are many things in this line what you want is one with a non-retrigerable monostable (I think...). You should be able to find that and one with changeover contacts. They are DIN rail mounting but a small enclosure isn't much or just mounted in a box.

ISTR that they are quite cheap =A320 to =A330 and the extra installation= effort of mounting a box and a few more terminations isn't great...

[dennis]

Normally projectors need the mains to be kept on for a few minutes after you have operated their off switch. This allows the fans to continue to cool the interior and/or lamp. You should never switch them off at the mains before they have gone through their shut down period as it reduces their life.

So what you actually want is a delayed switch off not a delayed switch on.

[Christian McArdle]

Yes. I misread the original request and solved the keeping the mains on long enough problem!

Christian.

[Dave Plowman (News)]

They all do - or rather I think they do. Certainly my DLP back projection TV does. But it obviously relies on just going to standby, as removing the mains entirely would require a back-up battery to run the fan, which runs for some minutes after switch off.

But if you do, it won't re-strike until it's happy.

[Dave Plowman (News)]

Same here. I don't think it will re-start until it's happy to do so, but unplugging it before it's ready would be a bad thing too.

[drbob]

I was told by the place I bought the projector that as long as the pj isn't moved and is given at least 5 minutes to cool, it doesn't matter when it is switched off at the mains and the fan just helps it cool more quickly (it delays restart around 90 seconds when put into standby), is this definately wrong?.

My pj is a budget model and I'm not sure if the delayed restart it enforces when in standby is a simple timer or if it does actualy check the lamp temperature before attempting to restrike the lamp.

With a delayed power *off* rather than delayed restart, someone could take the lamp out of standby after it has been switched off at the wall, only to have the power suddenly cut a couple of minutes later. The instinctive reaction then would be to immediately switch it back on at the wall - if the pj doesn't check the lamp temperature on startup, then this scenario could damage it.

[Calvin]

The post-lamp-off cooling requirement very much depends on your exact projector make and model but the problem is generally that the bit that matters - the anode and cathode of the lamp - requires forced air cooling for a considerable time after being switched off. Cutting off the mains during this time stops this cooling and stresses the lamp but whether it leads to premature failure is hotly debated. Most high pressure lamps will restrike for a few seconds after switch off and again once cool but generally the lamps power supply won't be able to generate a high enough voltage to strike the lamp when it's warm but not hot. I can't see why it would matter to try to strike the lamp in this state and to the best of my knowledge no-one designs circuitry to protect against this if you remove mains and reapply it. So the issue is not that you shouldn't switch it back on too soon after switch off but rather that you shouldn't remove the mains before it's properly cooled down.

[drbob]

Thank you very much for that explanation. It seems the shop I bought the pj from didn't know what they were talking about. Was their advice never to move a projector until it is fully cooled down also incorrect?

[DJC]

Projectors usually include an auto off feature. Press 'menu' on the remote, it should be somewhere amoung the options.

[Mike Dodd]

As I understand it...

Calvin's explaination is accurate and should be considered carefully. However, different manufacturers seem to place different focus on the power-down / power-up procedure. The best advice I can offer is to visit the manufacturer's website or read the manual.

Regarding the movement, the only thing I can think of is that the envelope of the lamp will be more susceptible to damage during the cooling cycle if jarred abruptly.

Have a search on Sanyo's website (I've been there since owning a Sanyo PLV-Z2 projector for the last 8 months) - they have a nice FAQ/horror-story about the effects of power-cycling the lamps.

My own advice would be - forget the ancillary device to maintain power to your PJ and adopt a common-sense approach to the PJ (remember, a spare lamp could cost upwards of £300). Also consider a cheapish UPS - despite your best efforts you never know when a power cut could occur; I have a small Belkin UPS (around £70) that feeds the PJ, Sky and DVD recorder from battery backup (at around 50% full load) and has filtered (non-backed-up) outlets for the TV (still need it!), AV-receiver and the various format converters used to feed the PJ. That way, I hope to be able to shut down the PJ without the loss of cooling should a power cut occur.

Mike

[Calvin]

As far as post-off lamp cooling is concerned my advice is to apply common sense but also to relax a bit. Consistently turning the projector off by pulling the plug is asking for trouble (although still not guaranteeing you'll get it). Occasionally suffering a power cut or killing the mains a little while after a lamp off won't do any harm so it's really not worth having a UPS.

The shop gave you good advice about not moving the projector while it's hot. Lamps run very hot and so generate enormous internal pressures. Obviously when they are in their highly pressurised state they are more stressed so more prone to break if jarred. If (when) you ever change the lamp take heed of the warning notice that will say to let the lamp cool completely before handling. UHP lamps (probably what you'll have in a domestic projector) are quite safe when cold but consider them a bomb when hot.

If you really want to look after your projector do two things. Give up/don't start smoking. It coats the optics. Clean the filters regularly. If it can't get air in it can't stay cool.

[Andrew Gabriel]

Many are bombs when cold too -- internal pressure can still be above atmospheric. If you drop or scratch them, they can still explode.

[Calvin]

You're correct Andrew, that was poor advice from me. While cold lamps are a lot safer than hot ones they should be treated with great respect (I usually call them "Sir").

[John Rumm]

If you were going to go to the bother of custom building, then I would include a inhibition of turning the power off while on load as well since most projectors require a controlled run down and cooling off period.

[Mike Dodd]

Calvin wrote:

Might be worth looking at

(41) - especially the last sentence re. power cuts. That's the basis of my advice (based only on the recommendations from the manufacturer of my projector).

The point on smoking is a good point, too.

PS. Bollocks, that link doesn't work - dynamic page contents...

Here's the text, anyway, can be found by going to links Business / Projectors / Home Cinema / FAQ

1. What causes lamp failure? Although it is hoped that a projector lamp will continue to operate satisfactorily throughout its anticipated working life, it has to be accepted that failure may occur before that anticipated time has elapsed. General Failure: The lamp in a projector is categorised as a consumable item, and even with proper use and maintenance a small proportion of lamps may fail well before their expected life span has elapsed. Neither the life expectancy nor the performance of a lamp can be guaranteed, and the duration of its useful operation will depend to a large extent on the conditions under which it operates. Usage Failure: As a projector lamp ages, the ends of the two electrodes within the strike chamber cavity gradually erode and the gap between them slowly increases. Erosion of these electrodes will occur every time the lamp is started and eventually, a point is reached at which the Ballast Power Unit can no longer supply the amount of current demanded by the lamp in order to strike and maintain the arc between the electrode tips. It is at this stage that performance deteriorates, with the light output falling off , the lamp starting to flicker at switch on or going out soon after strike up, or even failing to come on at all. Temperature Failure: Two factors that always result in high lamp glass temperatures are the non-adherence to correct power down procedures, and blocked or partially blocked air filters. It is essential that the projector be powered down properly after use in order to allow the cooling fans to reduce the lamp temperature sufficiently. The hottest part of a working lamp is the strike stem containing the two electrodes, and if the airflow over the lamp is in any way restricted by blocked filters, temperatures around the strike chamber will rise sufficiently to soften the glass. The usual consequence of this is that the pressurised strike chamber balloons outwards at its weakest point, producing a bulge or swelling in the stem. The stem itself is pulled off axis as a result, effectively moving the strike area away from the focal point of the reflector. Elevated temperatures can also generate microcracks in the stem, allowing the ingress of air that is then burned by the heat from the lamp arc, usually leaving black oxide deposits on the internal surfaces of the chamber walls as well as on the strike electrodes. The microcracks grow rapidly, and after a very short time the integrity of the structure is compromised and the stem shatters. Any mains voltage interruption or power cut, however momentary, will produce similar results to those outlined obove.

[Dave Liquorice]

I'm sure that the programmable/timer relays you can buy off the shelf will do that. See what RS have to offer.