Thanks folks again for this analysis. As I said I haven't looked into the devices in detail yet but if we assume each circuit will support 25 led (so 1 on each side of the path every 2 metres, assume each led is 1w so 50w total (might not need this many - depends on how much light is cast by each led) then without a relay both pir would need to support this. I have seen 12v pir devices that say they can support 100w so is a relay strictly necessary? I guess it could cost less overall so probably a good thing and also improve lifespan. Thanks again!

 

Thanks folks again for this analysis. As I said I haven't looked into the devices in detail yet but if we assume each circuit will support 25 led (so 1 on each side of the path every 2 metres, assume each led is 1w so 50w total (might not need this many - depends on how much light is cast by each led) then without a relay both pir would need to support this. I have seen 12v pir devices that say they can support 100w so is a relay strictly necessary? I guess it could cost less overall so probably a good thing and also improve lifespan. Thanks again!

No matter what the actual current is, it will all flow thru the PIR package unless a relay is used, and probably the devices rated to handle the larger loads will cost more because of the higher rating. At least that has been my observation.
Certainly both schemes will work, that was not my point at all. Cost reduction, both initially and over the system lifetime, along with a possible bit more reliability, was the anticipated benefit.

 

Understood thanks

 

One final question then..before I start buying lights. If we assume I'll fit low level led pathlights that produce 100 lumens how big should the interval be along the path between the lights assuming they are alternated side to side. The path isn't very wide - probably 3ft Any guidance much appreciated!

 

That is a difficult question because we do not know what the light pattern looks like, nor do we know how much light you need, (or want), nor do we know how far off the path the lights will be.
One common scheme would put them a foot off to each side, alternating sides, with the line between the lights crossing the path at 45 degrees, relative to the path center line. That would put the lights about five feet apart, with a light every two and a half feet on alternating sides.
For 50M, about 160 feet, that gives 160/ 2.5=64 lights, 32 on each side. The path would be well lighted, depending on how much the plantings shade the walkway.

 

That's very helpful - thanks

 

It is also a whole lot of lights. But it will be quite something at night. I hope that the PIR sensors are not like mine, which are also triggered by rabbits and squirrels running past.

 

Wow that's a lot of lights!
I'm thinking more like 16 per side.

 

We don't know about the pattern, or how far above the ground they are, or in which direction alll of the 100 lumens are aimed. I made a guess that they will be a foot off of the path, which puts the two rows of lights five feet apart. That would space them five feet apart between sides, ten feet apart on each side. If the lights are quite directional then it may be different. But most garden lights are not very directional, nor very bright.
What makes sense now is for the TS to buy a dozen lights and try and see before burying any wires.

 

Thanks again. I'm thinking the lights will be set into the side of the path with a hole cut into the edge paver. The lights will be directional with a 90 or 180 degree spread of light low across the path. I'm thinking I need to go for robust stainless steel lights. I'll see if I can post a picture of the type of light. I'll definitely test out a few lights before ordering the big batch! Unfortunately the one I have looked at so far are currently out of stock!

 

 

And here is a section of the path - currently showing some battery PIR lights that will be replaced!

 

I am going to suggest that you don’t need to light the path anywhere as bright as day. I have cheap solar powered garden lights spaced about every 3m reflecting off the lawn. I am going to guess about 10 to 15 lights should do it reflecting off the stone pathway.

To simplify the wiring, you can try putting them all on the same side of the pathway.

 

Thanks for the suggestions. I started with solar lights about 5 years ago and found that here in the UK they were simply too dim to be of any use in the winter (when we need the light). Also somewhat unreliable. Then I moved onto the battery PIR lights which were pretty good but needed lots of batteries and weren't really weatherproof. So, now onto the current scheme....which I have more confidence in for a long term solution. Thanks for the suggestions again though.

 

Oh Wow!! That is rather different from what I was thinking about, which was a "garden path" at one of the "southern estates" in our "Sunny South". One client/friend moved to such a year ago, putting a serious crimp in the business side of the relationship due to the 1000 mile separation.

YES, it will require quite a few of those low profile lights. And I recall that night time can be as dark as "a coal miner's back pocket", at least in the Birmingham area.

 

Yes! It doesn't help that the path is on a slope and twists through some trees at the top. It can also get slippery in the winter with frost/ice but that's a different issue!

 

Hi folks, a quick follow up to my last posts. Is it possible for a 12v DC relay (coil) and DC circuit to control/switch a 12v AC circuit? I'm assuming the DC relay will simply make a connection for the AC circuit? Thanks

 

Sure. The relay contacts do the switching

 

Like stated in post #38, YES!! That is one of the main uses of relays, is to have one voltage control another voltage.
But a bit of caution is to be aware of the relay specifications. Aside from the control coil voltage, the other important specs are the contact current rating and the contact voltage rating. In addition a relay with a DC rated coil MAY POSSIBLY BUZZ when operated on AC. BUT switching DC with an AC rated coil will be no serious problem.
AND another thing: Post #24 mentions LED path lights, and now I see "switching AC. The concern being that some path light types demand DC power. If the light are rated for AC power then there is no concern. If they are specified for DC, then with an AC supply rectifiers will be required.

 

Aside from the control coil voltage, the other important specs are the contact current rating and the contact voltage rating. {{ Thumbs Up }}

The type of lighting is important. Using LED's will draw very little current. Using regular lighting such as Halogen bulbs will draw significantly more current. The reason why I'm quoting Mr. Bill is because not only is it important to have the correct voltage and current it's also important to understand the differences between AC and DC current ratings. A relay rated to handle 120VAC at 10A doesn't mean it will handle 10A at 12VDC. Arcing could occur and even though the relay may disengage the current can still continue to flow when using DC on an AC rated set of contacts. That's why you'll often see 120VAC 10A or 12VDC 3A. Sounds non-intuitive, but that's the facts.

Also mentioned is using a DC coil on an AC source. It CAN buzz. In addition to this using the wrong coil (AC vs DC) can result in overheating of the coil. Overheating to the point where it can melt down or even start a fire. A relay is far more than just a switch. Choose wisely.