Layout lighting destroying transformers - what am I missing?

[tbdanny]

Hi all,

A few weeks ago, I finished installing the overhead lighting on my layout, and today is the first time I had a chance to try it.  Originally, it was powered by a voltage regulator circuit stepping down the voltage from an old laptop power supply.  However, this circuit failed and overheated, which I suspected was due to too much current (~5A) going through it.

I then replaced it with a 2.5A, 12vDC wall wart.  Today, I had the lighting on while working on the layout.  After about half an hour, the lighting turned off, and the plug pack was hot.  It won't turn back on, and I suspect my near future will involve a trip to the nearest electronics store for a replacement.

I know there's something here that I'm missing.  In both setups, the output of the voltage regulator is connected directly to the LED lighting strips.  Currently, the circuitry is as follows:

Plugpack --> 2.5mm line plug --> LED strips.

Given that the issue seems to be too much current flowing through and damaging the plugpack, I have a feeling I should be using resistors between the 2.5mm plug and the LED strips.  Is this correct?  If so, what wattage should I be using?

Cheers,
Tbdanny

[Southgate]

Well, it all depends on how much current the LED strips draw, and how many you're using. Driving a 5 amp load with a 2.5 amp supply is asking for trouble. Not just transformer burnouts but potential fire hazzard.  Adding resistors won't help if the LED strips are running at their rated draw. You need a higher current power supply.

 

[Soo Line fan]

Add a inline fuse slightly below the current rating of your power supply.

The fuse will open before the power supply can be harmed.

[Mark R.]

You're missing matching the power supply to the LED strips. You need to calculate the amperage DRAW of all your LED strips and use a power supply that is greater than the total current required by the LEDs.

Depending on the size of each LED and how many LEDs you are using, they could draw anywhere from 3 to 4 and even 6 amps per roll !

Example 1: A 5m roll of SMD5050 (0.24 watts) with 60LED/m would be: (5m x 60 x 0.24) / 12 = 6amps +10% = 6.6Amps.

Example 2: A 5m roll of SMD3528 (0.08w) with 60LED/m would be: (5m x 60 x 0.08) / 12 = 2amps +10% = 2.2Amps.

Mark.

[maxman]

Okay, I'll ask the obvious question...did not the lighting come with some instructions specifying the power supply?

[tbdanny]

maxman

Okay, I'll ask the obvious question...did not the lighting come with some instructions specifying the power supply?

 

They were LED strips purchased off Ebay and cut to length:

There wasn't anything in the way of instructions - just the LEDs on a reel.

[Bayfield Transfer Railway]

tbdanny

However, this circuit failed and overheated, which I suspected was due to too much current (~5A) going through it.

I then replaced it with a 2.5A, 12vDC wall wart.

 

Um.

 

Look at this part from your message.  Read it.  Read it several times.

[tbdanny]

Bayfield Transfer Railway

 

 

tbdanny

However, this circuit failed and overheated, which I suspected was due to too much current (~5A) going through it.

I then replaced it with a 2.5A, 12vDC wall wart.

 

 

 

 

Um.

 

Look at this part from your message.  Read it.  Read it several times.

 

 

Yeah, I realised as I was posting the inital message .  I was kinda carrying the idiot ball on that one.

I asked about increasing resistance as under Ohm's law, I=V/R, so a greater resistance would result in less current?

[hon30critter]

Greater resistance will result in less current but will also result in less light.

Get a proper power supply.

http://www.ebay.com/itm/S-120-12a-Super-Stable-Power-supply-unit-120W-DC-12V-10-5-13-8V-10AMP-/221944509237?hash=item33acec7335:g:gNsAAOxy-W9SQUm8

Dave

[Bayfield Transfer Railway]

If you have an old desktop, or know somebody who does, yank the power supply out of that.  Nicely regulated 12V and a pretty high capacity; 300 to 400 W.

 

[maxman]

Do you have a link to the ebay place where you bought those strips?  Maybe there was something in the description that states what the power requirements are.

Anyway, if those strips are anything like those sold by Micromark, Micromark states that the power requirement is 12vdc and 1.2 amps per meter: http://www.micromark.com/warm-white-high-intensity-led-flexible-light-strip-5-meters,10716.html.

Looks like you have several meters worth of LEDs.

[tbdanny]

According to the seller (http://www.ebay.com.au/itm/5M-SMD-300LEDS-2835-3528-5050-5630-Non-Waterproof-Waterproof-LED-Strip-12V-DC-/291301594973?var=&hash=item43d2ed975d) these strips (the 5050) are 1A = 1m.

I've done the measurements, and the length of the modules is 6.44m, x3 for the three rows of LEDs.  This gives us a total current draw of 19.32A.  A friend of mine has a couple of spare desktop power supplies he's happy to let me use, one of which is 500W.

[maxman]

tbdanny

According to the seller (http://www.ebay.com.au/itm/5M-SMD-300LEDS-2835-3528-5050-5630-Non-Waterproof-Waterproof-LED-Strip-12V-DC-/291301594973?var=&hash=item43d2ed975d) these strips (the 5050) are 1A = 1m. I've done the measurements, and the length of the modules is 6.44m, x3 for the three rows of LEDs. This gives us a total current draw of 19.32A.

I didn't see the current requirement in the link.  Did you have to ask them the questions and they responded?

Anyway, 19.32 amp would definitely be the reason you had a problem with your original wallwarts.

[Bayfield Transfer Railway]

Yeah, trying to push 19+ amps out of a 2.5 amp power supply, no wonder it went kamikaze.

 

[Mark R.]

Keep in mind you just can't pull a power supply out of a desk-top computer and use it without modification ....

http://web2.murraystate.edu/andy.batts/ps/POWERSUPPLY.HTM

Mark.

[BroadwayLion]

Mark R.

Keep in mind you just can't pull a power supply out of a desk-top computer and use it without modification ....

http://web2.murraystate.edu/andy.batts/ps/POWERSUPPLY.HTM

Mark.

 

 

Thanks. I was going to mention this, but I did not have the solution that you have so kindly provided.

I'll keep that page, because I have a whole box of dead power supplies and should like to be able to use them

ROAR

[tbdanny]

Mark R.

Keep in mind you just can't pull a power supply out of a desk-top computer and use it without modification ....

http://web2.murraystate.edu/andy.batts/ps/POWERSUPPLY.HTM

Mark.

 

Mark,

Thanks for the link.

[rrinker]

 I've tried a whole bunch and adding that load resistors have been pretty much unecessary. Maybe mine were better quality power supplies. Back in the 286 days, AST computers came with a load resistors in the case that you had to hook up unless you added a hard drive. Talk about low quality power supply...well, the whole things were low quality but that's beside the point.

 And especially if there is any sort of load on the power supply - the load resistor definitely is not needed.

As for the LEDs - the reel of RGB LEDs I bought, 3M worth, came with a 5A power supply. That's about standard for the 5050 strips and maybe for the ones that use more but smaller LEDs. So 15 meters worth will ned 3x the power, and so forth. Individual LEDs are low current but string together a few hundred and it adds up. There are also limits on how many strings you cna run end to end, because even if you supply the proper power, the printed circuit strips in each section will only be able to handle so much current - you can;t just keep stringing them end to end around your entire room and just have one power feed at the end. You need to have dedicated feeders for every couple of sections at least (I think I would just feed each section directly and never use the end to end connections). This also allows seperate sections limited with fuses or breakers - 20+ amps at 12V is 240+ watts which is plenty of heat to melt things or even start a fire. Rather than trying to make one 20 amp power bus, which would need somewhere in the neighborhood of #10 wire to not have excessive voltage drop, run seperate lines to each 3M section of LEDs, limited at 5 amps each.

                     --Randy

 

[tbdanny]

maxman

I didn't see the current requirement in the link.  Did you have to ask them the questions and they responded?

In the table in the eBay listing, it states that the 5050 LEDs (which I used) have a draw of 5A/5m.

rrinker

There are also limits on how many strings you cna run end to end, because even if you supply the proper power, the printed circuit strips in each section will only be able to handle so much current - you can;t just keep stringing them end to end around your entire room and just have one power feed at the end. You need to have dedicated feeders for every couple of sections at least (I think I would just feed each section directly and never use the end to end connections). This also allows seperate sections limited with fuses or breakers - 20+ amps at 12V is 240+ watts which is plenty of heat to melt things or even start a fire. Rather than trying to make one 20 amp power bus, which would need somewhere in the neighborhood of #10 wire to not have excessive voltage drop, run seperate lines to each 3M section of LEDs, limited at 5 amps each.

                     --Randy

This is the first time I've worked with a system that involves more than 4 or 5 amps, so I want to make sure I have my approach correct this time.

At the moment, none of the LED strips are connected end-to-end.  My layout is divided into 5 sections, the longest of which is 1.74m, and the rest are all around 1.2m.  Each section has 3 strips, all of which are connected with their own feeders, in parallel.  On each section, these feeders (on the top of the shadow box) go to a single pair of wires, which runs down behind the backdrop and joins the lighting bus.

Now this is where I think I'm going to have to redo the wiring, as the feeders, the wires behind the backdrop and the lighting bus itself are multi-core, 28AWG.  I've used this for feeders on my track & accessory bus without any issues.

I think what I need to do for the lighting is as follows:

1) Adapt the power supply from a desktop PC to drive the lighting.  This will be done by constructing a 'breakout box' with a matching connector for the standard plug on the power supply (similar to this: http://makezine.com/projects/computer-power-supply-to-bench-power-supply-adapter/).  This will have the load resistor (if needed), power switch and a bank of 5 circuit breakers.  One will be 7A (local electronics shop doesn't do 6A), and the rest will be 5A.  These will run to 5 pairs of connectors on the outside of the box; 1 pair for each section.  I'm also thinking of using an aluminum case, so it could act as a heatsink if needed.

2) Replace the feeders on the 1.74m section with heavier wire.

3) Redo the bus & backdrop wiring, with wires that are capable of carrying at least 7.5A - 13AWG or larger.  Each section of the layout will also have its own feed, directly from the power supply.

[rrebell]

Seems like a lot of amps for so little space, my entire layout uses less power, including the lights of which I have around 60 cfl's

[chutton01]

How many independant circuits does the OP have within his layout room, anyway?
Normally in North America outlets (well, actually the circuit is) are rated for 15A, with heavier duty 20A outlets (normally having a 'T' shaped neutral) - again, this is 20A per circuit.  This lighting scheme is some serious power draw, approaching stage lighting levels...

[middleman]

The 5050 LED strings draw 5 or 6 amps per 5 meters from a 12 volt source,so you're looking at a load of 72 watts(plus a fraction for transformer loss) or less per strip.  Roughly .6 amp(per strip)from your 120 volt outlet.

[tbdanny]

I'm getting a bit confused here. It is 72 watts or less per 5m strip, but as installed, these aren't 5m strips. They're cut to fit the layout section lengths, and the longest are 1.74m. Each power supply I've used has been 12v. There are three strips on each layout section, connected in parallel. I used 3 to eliminate shadows, especially against the backdrop.

[middleman]

Think of each 300 LED 5 meter strip as 100 groups of 3 leds.All the groups are wired in parallel,but the 3 LEDs in each group are wired in series. If 100 groups = 6 amps,then each group draws .06 amps. You can simply count the groups of three you have in your cut-to-length sections,and multiply by .06 to give you the amperage of that section.Do this with each section you have connected to the same power supply,and add those numbers together. That will give you the total amperage needed from that power supply. I like to size my power supplies above the amps needed by at least 25%. A power supply operating at less than maximum rated load runs cooler,and will likely last longer.

Mike

[Mark R.]

chutton01

How many independant circuits does the OP have within his layout room, anyway?
Normally in North America outlets (well, actually the circuit is) are rated for 15A, with heavier duty 20A outlets (normally having a 'T' shaped neutral) - again, this is 20A per circuit.  This lighting scheme is some serious power draw, approaching stage lighting levels...

 

20 amps from a 12 volt source draws considerably less amperage from the 110 volt main in the conversion. 

Mark.

[CSX Robert]

rrebell

Seems like a lot of amps for so little space, my entire layout uses less power, including the lights of which I have around 60 cfl's

 

 

chutton01

How many independant circuits does the OP have within his layout room, anyway?
Normally in North America outlets (well, actually the circuit is) are rated for 15A, with heavier duty 20A outlets (normally having a 'T' shaped neutral) - again, this is 20A per circuit.  This lighting scheme is some serious power draw, approaching stage lighting levels...

 

You guys are confusing current and power.  Power is watts, not amps.  20 amps at 12 volts is the same power as 2 amps at 120 volts.

 

[DigitalGriffin]

*shaking my head*

[tbdanny]

Power is volts x amps, is it not?

The desktop power supply I've got is 500W, and the mains AC voltage here in Australia is 240v.

So, on the input side, from the power socket;
500/240 = 2.08A draw

On the output side:
500/12 = 41.66A available.

Is this correct?

Will my approach of upgrading the wiring also work?

Depending on how bright the lighting is, I may drop the middle strings.

[rrebell]

Don't use 240 to fiqure things use 220. Here in the states the real available power is closer to 109 vs. 120 rated. I have very little knowlege of low voltage so will bow out of the rest of the discusion.

[rrinker]

rrebell

Seems like a lot of amps for so little space, my entire layout uses less power, including the lights of which I have around 60 cfl's

 

Yes but that's at 120 volts, 10x the voltage - so if all else were equal, 1/10th the amps. Even accounting for less than perfect power supplies, I'll bet the draw at the wall is far less than your CFLs. 5 meters, 15+ feet, of LEDs drawing 5 amps, that would need to be just half an amp at 120V with CFLs - pretty sure enough CFLs to light up 15 feet of layout would draw more than 1/2 amp.

                       --Randy