LED strips for Layout lighting

[HLT 0109]

I am having trouble getting the lighting right for the lower level of my extensive layout, which is about 15" below the upper level.  On part of the layout i have a 5m LED tape plugged into the ring main with the supplied power supply producing the necessary 12v.  I want to use another strip for the rest of the layout but do not want to use another 13amp socket - I want to wire it into the lighting circuit - perhaps by using a bayonet type of plug.  I have asked a supplier whose tapes have a moulded plug designed for a ring main, if the can supply a suitable transformer without a plug and they have said I don't need one as I can cut off the plug and wire the tape direct into the 240v supply, as it is the wires that reduce the voltage to 12v, not the plug.

 

I have never heard of this and can't really believe it - though I would like to.  I could source a transformer elsewhere but the supplier is saying it is not necessary.  Can anyone confirm (or positively refute) what the supplier is saying?

 

Harold.

[Baby Deltic]

I wouldn't try it personally. LEDs don't like it up 'em and it could be potentially very dangerous if he's wrong

[Griffin Road]

240 v led tape is available quite commonly nowadays . Usually you use a plug converter on the end rather that ' cut it off ' . I would have thought your supplier would have offered this rather than the advice he gave on a safety and sales aspect !

 

Just be careful though . 240 v and a wee dose of amps are a little dangerous as Baby D intimated .

 

Mike b

[PhilJ W]

12v LED's are available in strip form for use in caravans and campers. Try looking at the caravan and camping suppliers.

[melmerby]

I am having trouble getting the lighting right for the lower level of my extensive layout, which is about 15" below the upper level.  On part of the layout i have a 5m LED tape plugged into the ring main with the supplied power supply producing the necessary 12v.  I want to use another strip for the rest of the layout but do not want to use another 13amp socket - I want to wire it into the lighting circuit - perhaps by using a bayonet type of plug.  I have asked a supplier whose tapes have a moulded plug designed for a ring main, if the can supply a suitable transformer without a plug and they have said I don't need one as I can cut off the plug and wire the tape direct into the 240v supply, as it is the wires that reduce the voltage to 12v, not the plug.

 

I have never heard of this and can't really believe it - though I would like to.  I could source a transformer elsewhere but the supplier is saying it is not necessary.  Can anyone confirm (or positively refute) what the supplier is saying?

 

Harold.

 

LEDs will not work off 240v without some sort of voltage dropper/converter

 

If this item is like what was suggested by your supplier, the voltage conversion appears to be in the swollen bit of the cable:

 

http://www.mr-resistor.co.uk/item.aspx?i=16544

 

Keith

 

EDIT The 13A mains plug could be removed and the cable end wired in directly to the 240v supply

[28XX]

Or if you are not sure, use a 4 (or more) way mains extension cable. Although these are frowned on for running a toaster, kettle, fan heater and hair dryer simultaneously, LEDs take so little energy, it is an appropriate solution.

[brigo]

There are disadvantages with these 240v LED tapes.

 

They are fixed in length, you cannot cut them into shorter pieces like the 12v ones.

They are sheathed in clear plastic because the LEDs are not isolated via a transformer from the mains. If you cut through the sheath you can get a shock.

 

If you are considering these as being a permanent part of the household lighting, then OK, but remember if there is a fault you are relying on your main fuse box tripping out.. But if you are only going to plug in when required then a household lighting circuit is not really meant for this, there is no Earth connection on bayonet fittings.

 

I would always wire up a layout through an multi-way extension lead, preferably a switched one so you can turn off items not being used. Then by pulling the plug on the extension lead you have isolated the whole layout.

 

Brian G.

[Crosland]

The retailers advice is misleading at best, b******* at worst. Wires do not convert the 240V to 12V, the power supply does it. If the retailer can't explain that there is some form of power supply in the "wire" then it would be best to shun his advice completely.

 

If you are not confident, don't go anywhere near the 240V side.

 

Cut the 12V side and either wire the two 12V LED strings in series to a new 24V supply or in parallel to a new 12V supply with a curent rating adequate for both strings.

 

Andrew

[47137]

I have six metres of 12V LED strips lighting up my own layout and together they draw most of 3 amps from a 12V supply. When I built the lighting rig I cut them into four strips (each strip 1.5m long) and fed the power into them at one end. My write up is here and part 2 here.

 

When you look at the construction of these strips with their very thin copper tracks you do wonder if a single 5m length will run properly with a feed at only one end. My own recommendation would be to cut them into lengths of 2m or less, and use some stranded wire 7/0.2 or thicker to feed in the power at both ends of every strip. This will also give you some redundancy in case a connection fails.

 

It is worth persevering with these strips. When they are up and running you will find you can stand between them and the layout and your own shadow is minimal.

 

- Richard.

[HLT 0109]

Many thanks everyone for your comments.  I share Andrews advice that the retailer's advice is b*******.  I am quite interested in Keith's link but what the retailer was offering was not that.  I have considered a multiplug but none of my sockets is in the right place and I don't want any more trailing leads (I am running out of places to staple them out of the way).  I note Brian G's comments about 240v strips and now think it would be best to avoid them as the strips will be among/close to the 12v & 16v layout wiring.  All power to my layout room (loft) is switched off by a master switch when I leave the room; room lighting, layout lighting and layout power are separately switched and/or plugged.

 

Harold.

[melmerby]

There are disadvantages with these 240v LED tapes.

 

They are fixed in length, you cannot cut them into shorter pieces like the 12v ones.

They are sheathed in clear plastic because the LEDs are not isolated via a transformer from the mains. If you cut through the sheath you can get a shock.

 

That's why the one I linked to can be cut then?

 

Keith

[brigo]

That's why the one I linked to can be cut then?

 

Keith

 

Yes and no. The blue and white strips are 1200 mm long and cannot be cut. They consist of 72 LEDs. The reels can be cut into 83 lengths of 1200 mm. The amber are 2000 mm long and consist of 120 LEDs and the reels can be cut into 50 lengths.

The LEDs are connected in series, so for the blue and white strips each LED has a Forward Voltage drop of about 3 volts. 72 times 3 equals about 216 volts. The remaining volts of the 230 volt mains supply will be dropped through a current limiting resistor and a rectifier which will be in the blob on the cable. The amber LEDs have a smaller Forward Voltage drop, just under 2 volts, so you need more of them.

 

Brian G

[Crosland]

When you look at the construction of these strips with their very thin copper tracks you do wonder if a single 5m length will run properly with a feed at only one end.

 

 

They do work as the current reduces as you go along the strip as some of it is diverted through the LEDs. By the time you get to the far end of the strip only the current for a single string of three LEDs is flowing (they are usually arranged as groups of three series connected LEDs with a resistor, many such groups connected in parallel). So the highest current is only present at the input end of the strip and only flowing in a very short length of that thin track. Each time you come to a group of 3 LEDs the current for that group, say 10mA, is diverted and then flows along the return path to the supply.

 

Andrew

[Crosland]

Yes and no. The blue and white strips are 1200 mm long and cannot be cut. They consist of 72 LEDs. The reels can be cut into 83 lengths of 1200 mm. The amber are 2000 mm long and consist of 120 LEDs and the reels can be cut into 50 lengths.

The LEDs are connected in series, so for the blue and white strips each LED has a Forward Voltage drop of about 3 volts. 72 times 3 equals about 216 volts. The remaining volts of the 230 volt mains supply will be dropped through a current limiting resistor and a rectifier which will be in the blob on the cable. The amber LEDs have a smaller Forward Voltage drop, just under 2 volts, so you need more of them.

 

Brian G

 

These are best avoided. They are like christmas tree lights where a single failure takes out the whole series string.

 

Andrew

[Crosland]

Just a thought on the 5m strips. If you were to cause a short circuit at the far end from the power supply, then all of the current will be flowing along the whole length of the strip. If you use a sensibly rated power supply then it should shutdown before any damage occurs.

[Darwinian]

I am using a 5m strip of 5050 Daylight LEDs to light my layout. At the moment they are just hung over the layout and connected at one end only.

For the power supply I'm using the 12v output on my Morely Vector controller.

I have a 12v car accessory supply unit from maplins but that is being used to run the Fulgarex point motors on the layout but I was concerend that i might overload this if I conected the lights to it as well.

 

When I turn on the lighting all is fine but after about 5 minutes the brightness drops by about 40%. Turn off the juice and turn back on and they return to full brightness.

 

Any ideas as to why?

 

Adrian

[smokebox]

You are probably overloading the Morley controller. What power do the LEDs take? You should be able to measure the current taken with a meter if it's not specified.

[RAF96]

Some wall wart PSUs overload protect by dropping the voltage rather than tripping out and your controller seems as if it is doing this.

 

As an aside - The Hornby Select controller 1Amp power supply uses this principle and the effect of the volts drop is to reboot the controller, a sure indication of an overload. In this case the controllers own overload trip protection is set higher to allow it to be used with the bigger 4 Amp PSU.

[Baby Deltic]

Ideally for LED's you'd probably be best off getting a variable voltage constant current power supply where the current is always fixed at a level which will power the LED's but the voltage will automatically increase to maintain the current when more and more load is added. I recently picked up a 3 to 21V constant current mains LED adaptor rated at 700mA. Obviously with that current output it is designed for LED's with additional internal circuitry but a small resistor could be added if the sum of the current drawn by the number of LED's added to the circuit is less than 700mA.

[Darwinian]

Thanks for the helpful advice.

On checking I find that the LED strip lights are rated at 12V and 72W. Without a new battery for my multimeter I can't be sure what current they draw but suspect they are indeed drawing too much for the output from my controller .

The power suppplies sold to go with the strip lights are 12V, 6A and 72W so I guess I'd better buy one of those!

The power supply I use for my pouint motors is only 5A 60W so probably isn't enough to do both jobs.

 

 

(Edited for typos).

[dhjgreen]

W=VxI so 72 watts draws 6 amps

[Darwinian]

I think overall this just reflects that it doesn't pay to be lazy.

 

I know enough DC electrical theory to know that V=IR and P=IV etc. and how to use those equations. However I didn't check what the output of the Morley controller's auxilliary 12v DC output was. A good job the designers had forseen such foolishness.