Heavy Duty Photo Electric Switch ??

[delgriffith]

Hey there again, well I got a nice LED light on my back wall now, thanks for the responses on that issue. It's working well on a photo switch that was only like $14 or something. But now I am interested in switching on all the front Metal Halide lights with a photo switch like this. Right now they are on a timer, which is of course subject to change with the seasons and is often either wasting electricity or not on when we need it. We have 17 400w metal halide bulbs though, and by my calculations that could be around 60 amps / 7500 watts. What kind of hardware would I need to switch this on and off with a photocell? I'm guessing a relay is necessary, but not sure where to look to find what I need.

Thanks for any pointers!

 

[CoveAxe]

I doubt you're going to find a simple photo switch that can handle that much power, though someone with more experience in this could tell you for sure. I think you would have to build something custom, which I wouldn't recommend making yourself unless you knew what you were doing.

Why not just put a photosensor on each light? It would be a lot cheaper and easier to do, to be honest.

 

[brickbat]

All those fixtures on one circuit? Really?

What voltage ? Single or 3-phase?

Either way, the answer is likely to be "lighting contactor". Google it up, and if you don't understand what you find, call an electrician...

 

[delgriffith]

I doubt you're going to find a simple photo switch that can handle that much power, though someone with more experience in this could tell you for sure. I think you would have to build something custom, which I wouldn't recommend making yourself unless you knew what you were doing.

Why not just put a photosensor on each light? It would be a lot cheaper and easier to do, to be honest.

No I didn't expect to find a 7500w photo switch, but a photo switch that could trigger a relay, maybe. I'm learning that the term "Contactor" is helpful for finding what I might need. All lights are currently turned on by one timer, but I think there are actually two breakers for the lights, one with 12 fixtures and the other with 5. Still it seems like the full current must be going through the one timer that I'd like to replace with a photosensor system. I may need to investigate it further to get the correct information.

As far as putting a photosensor on each light, I'm not sure that would be cheaper or easier considering I'd be paying $14x17 and climbing up onto a 20' high canopy to wire in 12 fixtures and then four equally high fixture posts. And maintaining those sensors over time. That doesn't sound like much fun versus wiring in a new device into the timer's spot and running some wires outside to a photosensor. Here's a 60 amp relay that gets pretty close to what I need I think, when paired with a $14 photosensor: http://www.smarthome.com/elk-heavy-...-metal-structured-wiring-panel-enclosure.html Two of these wired in parallel would handle 120 amps and since the coil current is 35 mA, a photo sensor could easily trigger the two relays.

I can guess what might work like the idea above but I was just hoping maybe someone here knows what equipment is best for what I'm trying to do. I'll call in an electrician if need be, but I'm a hard core DIY'r with a couple engineering degrees and a healthy tolerance for accepting risk of the unknown. So I'm a little stubborn on paying someone thousands for a couple hundred in parts and a couple hours of labor.

 

[yuandrew]

I do know there's the Fisher Peirce 63300 series high-capacity photo-control which can switch 30 amps per pole. You'll need a meter socket to put it in

http://www.fisherpierceolc.com/pdf/FP63300_Series.pdf

 

[SemiMan]

Are you sure they are 120V and not 277V?


When switching ballasts, contactors are normally rated for a lower current than resistive loads. You will likely need a 100A contactor.

 

[CoveAxe]

climbing up onto a 20' high canopy to wire in 12 fixtures and then four equally high fixture posts.

Fair enough. I had just assumed that the power to the fixture was accessible from the ground in some way.

Before I comment further, what is the current rating for the timer, and does that also use a relay?

 

[Conte]

Rigging that much lighting is going to require some sub distribution. It's unlikely you'd be putting that all on one power run.

That "Smarthome" box could technically do the job if it indeed can handle 60 amps, but one box alone would have to do the job because it's unlikely electrical code would allow 2 in parallel. Not off the same 240v service that is. 2 separate services independent of each other yeah.

Either way, after that switching panel, you'd likely need a sub panel with breakers to distro power to the individual lamps. Probably like 2-3 lamps per breaker.
It's not going to be a cheap hookup. Certainly more than "$14x17" to do the job right.

PS: I'm an electrical technician. I work in the entertainment industry and have designed, built, and operated commercial lighting rigs. I'm no stranger to rigging up dozens of 500+ watt lamps.

 

[Qship1996]

Why not just adjust the present timer settings once per quarter to closer match dusk to dawn times..........not that big of a task to do only 4x a year?

 

[CoveAxe]

I never got a response, so I'll just post my opinion anyway.

Two of these wired in parallel would handle 120 amps and since the coil current is 35 mA, a photo sensor could easily trigger the two relays.

As Conte already pointed out, it's almost certainly going to be against code to put those in parallel, and a bad idea either way. This is because relays don't switch at exactly the same time, and also because relays fail. During the time that only one relay is contacted, it will be handling all of the current. Also seeing as these are MH lights, as SemiMan mentioned, they will have a large inrush current because of the ballast. So a single relay is going to be handling much more current than it's supposed to for at least some period of time. That's bad. You will probably need some kind of expensive commercial system to do what you are wanting to.

I was asking about about the switch in the timer because it may be possible to modify that to do what you want if it is properly rated for the current (which I'm assuming it is). Depending on the timer and your technical expertise, a small Arduino could be programmed and interfaced to do the time shifting automatically. This would also be much much safer since you're not messing with the high voltage side.

If this were me though, I'd just wire these up separately. Or just keep manually changing the timer for a while longer and use the money to upgrade to newer lights that use less energy and do this automatically from the fixture anyway.

 

[delgriffith]

Why not just adjust the present timer settings once per quarter to closer match dusk to dawn times..........not that big of a task to do only 4x a year?

I'm in a relatively northern latitude and so there is a pretty good swing in dawn/dusk times - around 7 hours. And I like to automate tasks. I find the more I can automate and eliminate human factors, the more reliable and efficient things get. Plus I don't have to train employees to adjust the time and follow up that they are doing it, or do it myself.

Upon further investigation, the lights are actually broken into at least four separate circuits. The timer is an Intermatic T103. That only has a 40amp rating, but I'm guessing that might be per pole and the circuits are split evenly between the poles so that they aren't over 40 amps. It makes sense that you shouldn't wire relays in parallel to handle a high load. Easy enough to just keep separate circuits.

So looks like replacing the timer with a couple of those Elk Relay-Contactors wired to the $14 photocell should do it. I'll be slowly replacing the Metal Halide fixtures with LED, so if the current draw is too much now, I can wait until I get it down some. I have a clamp meter to check that with.

 

[KXA]

To the OP, most likely there's a contactor already installed somewhere in your building that the timer is controlling. I've never seen a timer that could handle that kind of load directly. Look in your electrical panel for a label that says something to the effect 'lighting control circuit', usually a single pole breaker. That would be the circuit that runs the time clock which in turn controls the contactor.

As to contactors, has no one ever heard of one that can control multiple circuits at the same time? If you have line to line voltage, (208, 240 or 480 etc.) you would need a four pole contactor (two poles for each circuit). If you have line to neutral (120, 277 or 347) then you need just a two pole contactor (no need to switch the common conductors).

 

[jeffsf]

You don't want to mess around with 8 kW and a half-as, err half-baked solution. You definitely want to find the existing contactor (relay) or have one professionally installed.

For control of the contactor, another option would be the Honeywell Econoswitch RPLS740B 7-Day Solar Time Table Programmable Switch for Lights and Motors (or similar). That specific unit compensates for day-length (enter lat/lon of your location), as well as being able to set up an offset to local sunrise and sunset times. It is remarkably easy to program compared to some of the ones I've previously tried.