Is there an LED driver (transformer) that'll connect to my controller to drive some L.E.D lighting?

[topsy11]

Hello pretty much as the title really.

 

I've run a DCC ringmain around my layout and also considering running a DC main to power the point motors/signals etc as it seems to do the job just as well for what I require.

 

I'm wanting to power some L.E.D's in my diesel depot and so require a small transformer/driver to power these.

 

Ideally I want something that'll connect to the DC/DCC ring and then feed my LED's. However I can only find transformers that run from AC power and convert to DC which I'm guessing won't do what I require?

 

Thanks

Mark

[Edwin_m]

If they are small LEDs such as we usually use for models, then all you need for a DC bus is a dropper resistor in series with the LED - the resistance affects the brightness of the LED but 1k is a good starting point.  If powering from AC or DCC you also need a bridge rectifier or some other arrangement involving diodes.  Transformers etc are only really for power LEDs such as those that replace domestic light bulbs. 

[topsy11]

Thanks for the quick reply.

 

I'm wanting to run 3 x 0.5w SMD 5630's bulbs. So I could potentially wire them up from the DC ring with a suitable resistor in place?

 

Thanks again

Mark

[Edwin_m]

Thanks for the quick reply.

 

I'm wanting to run 3 x 0.5w SMD 5630's bulbs. So I could potentially wire them up from the DC ring with a suitable resistor in place?

 

Thanks again

Mark

Probably not at that wattage!  You also need to think about heat sinking for something that powerful. 

 

The LEDs usually seen on models are around 50mW and from what I've seen at exhibitions they light the interior of a largeish building quite well (remember they produce about 10 times as much light as a filament lamp of the same wattage).  Adding more LEDs at a lower wattage (each with its own series resistor) is also likely to give a more even illumination than using a few of very high wattage, likely to be more realistic given that the prototype will be lit by a large number of lamps. 

[clecklewyke]

If they are small LEDs such as we usually use for models, then all you need for a DC bus is a dropper resistor in series with the LED - the resistance affects the brightness of the LED but 1k is a good starting point.  If powering from AC or DCC you also need a bridge rectifier or some other arrangement involving diodes.  Transformers etc are only really for power LEDs such as those that replace domestic light bulbs. 

I've bought a 5m strip of LEDs which I hoped would light my small diorama, Royston Vasey but trying it on the 12V DC output of a working controller, on either polarity setting, elicits no light. Neither does it on a straight 16V AC output from a normal transformer.

 

I am worried that using reverse polarity or straight AC might have burnt out the LEDs but I cannot see why as they are, after all, just diodes, which pass current in one direction.

 

Any suggestions as to what I am doing wrong? Or have I just got a faulty set of diodes?

 

Ian 

[Tricky Dicky]

I've bought a 5m strip of LEDs which I hoped would light my small diorama, Royston Vasey but trying it on the 12V DC output of a working controller, on either polarity setting, elicits no light. Neither does it on a straight 16V AC output from a normal transformer.

 

I am worried that using reverse polarity or straight AC might have burnt out the LEDs but I cannot see why as they are, after all, just diodes, which pass current in one direction.

 

Any suggestions as to what I am doing wrong? Or have I just got a faulty set of diodes?

 

Ian

 

If you are trying to light all 300 then your power supply may not be delivering enough current. A white LED typically needs 30mA+ at its brightest. Depending on how the LEDs are wired that that could be as much as 30mA x 300 but it is my experience with these strings of LEDs they are usually wired in groups of three in series with a single resistor for each group of three but that is still 30mA x 100.

 

Richard

[Crosland]

The first product on that link is 36W/5m so you will need a 3 Amp supply to light the whole string. I imagine they are all similar.

 

Andrew

[SHMD]

I am worried that using reverse polarity or straight AC might have burnt out the LEDs but I cannot see why as they are, after all, just diodes, which pass current in one direction.

Never think of LEDs as "just diodes"!

 

Yes they pass current in one direction BUT this is only a small current.

Yes they block current in the reverse direction BUT this is only for SMALL voltages - typically 5 volts.

 

 

Correctly used they run cooler and last much longer than a filament bulbs.

 

 

Kev.

[Crosland]

Yes they block current in the reverse direction BUT this is only for SMALL voltages - typically 5 volts.

 

Compared to at least 50V for something like a 1N4001.

 

Andrew

[clecklewyke]

Never think of LEDs as "just diodes"!

 

Yes they pass current in one direction BUT this is only a small current.

Yes they block current in the reverse direction BUT this is only for SMALL voltages - typically 5 volts.

 

 

Correctly used they run cooler and last much longer than a filament bulbs.

 

 

Kev.

 

So, is it likely that I have damaged them by passing 12V in the wrong direction? If they are made in parallel groups of three LEDs in series that would be 4 volts each.

 

Thanks for all the other comments chaps. I did A level physics but in my day it didn't go beyond valves. A semiconductor was a faulty soldered joint. 

[SHMD]

So, is it likely that I have damaged them by passing 12V in the wrong direction? If they are made in parallel groups of three LEDs in series that would be 4 volts each.

It's hard to say but I would have thought you would have at least seen something.

Maybe, if you are lucky, there was another problem (wiring, fuse, wrong connections, etc) that meant no volts got to the LEDs.

 

 

12v dc reversed wont have done em any good but it is the 16v ac that would have really killed them.

The 16v ac would have been ALOT higher across the LEDs, at certain instants, as the peak-peak voltage would be 2*root(2)*16 = 45v!

(Of course the load LEDs, in both forward or reverse bias directions, would change this both down and up!)

 

The easiest way to power these LEDs would be with an old laptop PSU - as long as it was 12v dc AND capable of delivering 4 amps or more.

This would also have the advantage of being "doubly insulated" thus making it safer and easier to PAT Test. AND they are dirt cheap too.

 

 

Kev.

[Tricky Dicky]

So, is it likely that I have damaged them by passing 12V in the wrong direction? If they are made in parallel groups of three LEDs in series that would be 4 volts each.

 

Thanks for all the other comments chaps. I did A level physics but in my day it didn't go beyond valves. A semiconductor was a faulty soldered joint. 

I do not know where you get the 4V? White LEDs usually require a higher voltage compared to standard LEDs about 3V. Three in series require 9V then there is the current limiting resister wired in series which accounts for the remaining 3V (Ohm's Law). With regards reverse voltage it is commonly higher than forward voltage, therefore if the appropriate current limiting resistor is used your LEDs should not break down if polarity is reversed. I still think your main problem is your PSU is not supplying enough current. Having read the specs. 36W per 5m will require a 3A supply as Crosland said. Even the seller advises a buyer who submitted a question to buy a 6A supply.

 

Richard

[billbedford]

I've bought a 5m strip of LEDs which I hoped would light my small diorama, Royston Vasey but trying it on the 12V DC output of a working controller, on either polarity setting, elicits no light. Neither does it on a straight 16V AC output from a normal transformer.

 

Any suggestions as to what I am doing wrong? Or have I just got a faulty set of diodes?

 

If you go back to the Amazon page you bought the LEDs on you will find that they offer a package that contains the lights, a socket and a power supply. This last is rated a 6amps, I doubt your controller is rated at much more than 1 or 2 amps, and it may mean that you have blown the fuses in your controller, or at least tripped it out.

 

There is a good reason why these strips are sold with their own controllers, though you have to be aware of the real meaning of the price of Only a fiver.....

[clecklewyke]

If you go back to the Amazon page you bought the LEDs on you will find that they offer a package that contains the lights, a socket and a power supply. This last is rated a 6amps, I doubt your controller is rated at much more than 1 or 2 amps, and it may mean that you have blown the fuses in your controller, or at least tripped it out.

 

There is a good reason why these strips are sold with their own controllers, though you have to be aware of the real meaning of the price of Only a fiver.....

Thanks, Bill and everyone else.

 

I've taken the plunge and gone for the compatible 6 amp power supply (but not the plug - the supply has the appropriate male connector). We'll see on Wednesday whether the LEDs have survived!

 

Ian

[Crosland]

So, is it likely that I have damaged them by passing 12V in the wrong direction? If they are made in parallel groups of three LEDs in series that would be 4 volts each.

 

It's more complicated than that since there is also a current limit resistor in the circuit. The chances are that you will be OK.

 

The 16V AC is more of a problem as it will be over 20V peak voltage. You are still probably OK as, again, you have a current limit resistor and half of the time the LEDs are reversed. Flashing bike lights work by driving the LEDs harder than you would normally to get a bright light, but only, say, 50% of the time.

 

That just leaves the power supply.

 

Andrew

[14Steve14]

When the leds you bought were rated at 12v what in the name of all that is holy made you think that 16v would be ok. You may be lucky.

 

Go out and buy a 9v pp3 battery, one of the rectangular ones. Connect this battery to your leds and the whole 5m reel should light. Mine do. The 9v means they are a bit dimmer than if using 12v, but you can check that they work.

 

If not you will have to buy some more and be more careful with them.

 

The output rating of your controller may nor be high enough as many have stated.