Hi-Lo dimming of outside LED lighting

[stevie-g]

Hi All, newbie alert so please forgive me if I got the wrong forum area.

As per title, I'm trying to Hi-Lo dim a bank of outside LED lights.

I'm encountering that finding a stand alone Hi-Lo PIR suitable for LED's is virtually impossible, so thinking about creating my own solution within an IP enclosure as per image attached. Pleas excuse the crude drawing, I was trying to make sure my cable runs were do-able more than anything else!

Essentially what I'm trying to do is :

• On sensing dusk, the lights will come on via the dimmed circuit if the timer is on.
  
• The reason for the timer in line with the dusk sensor is that I want lights to come on when it gets dark, but I don't want them on all night, so will probably time them out after 11pm.
  
• The dimmer is in line with the dusk sensor circuit so that under normal conditions the lights only come on to say 20%.
  
• The dimmer will be a trailing edge type suitable for LED's.
  
• There is then a separate PIR with a timed "on" period contained within it so should it be activated, the PIR will then put full voltage on the output side of the dimmed supply and the lights will go to 100% before returning back to the 20% setting.
  
• There is also a 2nd PIR at the other end of the area I'm lighting to serve the same purpose.
  

I think this will work, my main question is, is it ok to have the dimmed 20% supply connected to the supply that will go 100% when the PIR activates. Will the 20% switch mess with the PIR output and vice versa will the 100% output from the PIR mess with the dimmed supply? I can't see why not, but wanted to see if you guys had a better way of doing it.

Thanks.
Steve.

 

[Lurch]

First thoughts are that the lights will need to be dimmable, most will contain a standard power supply of some description so this might not work without replacing parts of the control gear of the lights. Also the dimmer may or may not like a full voltage to appear on the output. To get around that you could install a changeover relay/contactor to switch the lighting feed from dimmed to full when the PIR activates instead.

 

[stevie-g]

Hi Lurch,

yes the lights just house a standard GU10 led lamp, so no jiggery pokery required to make them accept a dimmed supply, just a dimmable LED lamp.

Regards the changeover relay, thats a good idea and will resolve any potential problems with putting the full supply on the dimmed output and vice versa. I'll use the PIR output to feed this changeover relay and use the same PIR output to then switch onto the lamps.

Thanks.

I'll let you know if it worked when I get chance to buy everything and wire it up!

 

[Richard-the-Ninth]

Only thing I am wondering about is back emf from the relay, it may "fry" the pir (all be it slowly)

I would also ask why are you doing this, since all the components you are buying will cost more than you will save in electricity by dimming them.

The other (and cheaper) option would be:

LED  lamps 1, 2, 3, 4, 5, 6, 7, 8, 9, 10

To have the odd numbered lamps to come on at dusk and the even numbered lamps to come on with the pir.

 

[Tony S]

You could get around the back EMF problem with a MOV (Metal Oxide Varistor) over the relay coil but it’s adding more expense. Switching alternate fittings would be the best option.

 

[user 28595]

The relay in the PIR doesn't fry the PIR, so I think an external one is unlikely to do so.

cheers, Paul

 

[stevie-g]

Hi Chaps, to answer a couple of questions :

I would also ask why are you doing this, since all the components you are buying will cost more than you will save in electricity by dimm

Its purely about aesthetics, not cost. I essentially have quite a long driveway (approx 25 meters) and a side access down the house (another 15 meters) that I want to be lit enough to see well when the lights are on full. However, I don't like the look of the lights being on full tilt all the time during dusk hours, but I don't want them completely off either. So, I'm looking for a dimmed look when lights are not active, purely for aesthetics, then they come on full brightness to help you see when you need them.

To have the odd numbered lamps to come on at dusk and the even numbered lamps to come on with the pir.

I did think about this, but again it comes down to aesthetics. I'm not keen on a lighting display which when active would have each alternate light full, then dim, then full, then dim as it went down the length of the drive, I don't think it would look right.

The only other thing I can think of is to compromise slightly and choose a wattage which is in between a low level mood and full on illumination. Then, still have a timer (say a switch timer in place of the standard light switch in the house) to force the lights on for mood until around 11pm, then the timer goes off leaving the PR function enabled to come on outside of that time period? Would this be a much simpler solution if I made this compromise?

 

[Richard-the-Ninth]

 I'm not keen on a lighting display which when active would have each alternate light full, then dim, then full, then dim as it went down the length of the drive, I don't think it would look right.

But I never said that.

I said

 To have the odd numbered lamps to come on at dusk and the even numbered lamps to come on with the pir.

 

[stevie-g]

Ok, it must be my interpretation of what you're saying, but in my mind, if the odd numbered lamps come on at dusk and the even ones come on with the PIR, does that not mean when both are active I would have dim odd numbered lamps and bright even numbered lamps??? 

The only way to not have that happen would be to incorporate a further change over relay which would remove the dimmed supply from the odd numbered lamps whilst at the same time applying a full supply onto the even numbered lamps, which would beg you to ask why don't you just do that with one set of lamps instead of 2?

Or am I totally not getting what you're suggesting?

 

[M107]

Far easier

http://www.f4enterprises.co.uk/mightylite/mightylite-elite-pir-led-wall-lights/

 

[SPECIAL LOCATION]

Just thinking this through....

1/ A lot of bog-standard PIR switches have a relay contact as the output to switch 230v to a load.....

So if this relay contact is wired in series or parallel with other switching devices its unlikely to have any effect on the PIR sensor detection circuit that triggers the relay.

2/ A lot of bog-standard dimmer switches can be used as a two-way switch... 

where the dimmer could be put at either end of the two-way circuit..

and the common can be connected to either supply OR load without any detrimental effects....

3/  So..

If you wired such  a dimmer in parallel with a standard switch OR a PIR relay contact switch

all you will do is put a 230v potential at both side of the dimmer..

so the potential difference across the dimmer circuit will be 230v-230v =0v

Cant see how this would damage the dimmer circuit...

:C

 

[stevie-g]

Far easier

http://www.f4enterprises.co.uk/mightylite/mightylite-elite-pir-led-wall-lights/

Agreed, the problem with using this setup is the length of run I'm illuminating (approx 35m) and the number of units I would need. 

No doubt these units are probably reasonably expensive and they would all trigger independently when activated, where I want 1 PIR to activate the whole circuit.

Like the sound of Special Location's idea. Going to sketch that up now.....

 

[Richard-the-Ninth]

Ok, it must be my interpretation of what you're saying,

Or am I totally not getting what you're suggesting?

Yep, totally not what I said.

I will try again.

When its dark, the odd numbered lights come on.

When the PIR detects motion the even numbered lights come on.

That's it.

No relays, no dimmer, no complicated wiring.

I figure no dimmer as only every other light will be on, and this will be enough to see anything with, and when you move (or the wind blows) the other lights will come on.

I don't see the point of going to the expense of dimming the LED's in this case* as it's more to go wrong and you will not save any noticeable money.

* Dimming an RGB LED to get the colour combinations yes, but white LED's on their own, no point.