DC POWER SUPPLY

The technical answer depends on what LED's you are using....they come in so many varieties and how many per foot. Some are every .5 inch!!  But as I am working with a bunch of different LED's lighting a Star Trek Enterprise model.....it sounds like you have enough power......but plug in one set....the power supply will phase in and out if there's an issue! If you know your LED specs there is a formula online that tells you exact.

I was thinking about the 5mm 300 led reels,i would need 2 reels for my project,if this helps any.

Probably enough to power many more.  I have a bunch of the old Lifelike-AHM 7 watt 0-16 volt power supplies (as supplied by K-Line and Lionel with 'Streets RTR sets, and Lifelike HO starter sets).  One of these will run two strings of 30 foot LED "ropes" I bought and ran over the layout to add some more light. 

Thanks all for your replies,it will be a awhile before i get to that point,but when i do i will order the 2 reels & see how they work,if i have to get a bigger power supply then i will,but i will try what i currently have first.

It takes 12 volts at 24 watts to light a 300 LED strip to full intensity, so for two it would be 48 watts.

 

Computation.

 

100 3-LED groups groups times .02 amps each times 12 volts = 24 watts

 

I see Dale already computed it.  I'd get a bigger supply...

 

 

Gunrunnerjohn, is there any risks to using what i have to light the 2 reels other than not being able get to full brightness?,i may not want to have it to bright anyway,i have no problem getting another power supply if i have to,just curious .

It depends on the power supply.  You are asking it to deliver more power than it's designed for.  It may just degrade gracefully, or it may pop a gasket.

 

I think that i will just get another power supply,why take any chances it isn't worth the risk, thanks for your response.

Dale  H, I don't even know what a rectifier is ,now we are getting into something that i know nothing about,i have to keep it as simple as possible,for my simple mind,but thanks for the suggestion anyway.

Dale  H, You got my attention now,it looks like i may be able to do this,if i  give it a try would this be enough voltage  to run 2 reels of 5 mm led lights without any problems?,if yes would i be able to run additional led lights on this same 10-12 volt tap? One more questionon the bridge rectifier,is there a certain voltage rating i need to get?,or just any bridge rectifier?   Thanks again for your help.      Gerald  Marafioti

Look for a bridge that has at least a 5 amp rating (more if you want to run more strips), and 50V or higher voltage rating.  Dale's suggestion for a 10A one is probably good, as it'll be loafing and probably not get as warm.  Like Dale says, wire the AC input terminals, those are the ones with the ~ symbol to the 10-12 V tap, and the +/- terminals to the LED strips.

 

Job done.

Gunrunnerjohn,Many thanks to you & Dale H,for your help you both have given me enough confidence to try & do this myself it will be awhile before i get to this project but i have printed out what you both have posted to keep for future reference,i will be laying some track probably in the next week or so,as i have finished the bench work on the first level of my layout do over,i will continue to post pictures as i make some progress.

A 60 watt Led constant current  power supply is usually good for approximately 50 ft of most of quality Led strips. I do not know about the inexpensive no name imports.
Usually the modules run 2.5-3 per ft.
And keeping the power supply a maximum of 50 ft away using 12 gauge wire is the industry standard. I would load your power supply to the max. They run best that way.
If overloaded, they will let you know. Constant current LED power supplies have good internal thermal overload protection.
Unless you are recycling computer power supplies. Then I say, save a few pennies and make sure your breakers and smoke detectors are up to date.
Lol.

A constant current supply will handle anything you put on it, but not necessarily at full intensity. They're "overcurrent" protection is simply they won't supply more current!  You can directly short a constant current supply, it's as happy as a clam, just giving you the rated output current at about .1 volts.

 

However, a supply that wants to supply a constant voltage will get testy when you try to ask for more than the rated output.  They have no such limiting, at least most of the cheap ones we talk about here.  Hopefully, they at least have a circuit breaker or fuse...

 

 

Hi John,
You are correct. I was not talking about the clever work arounds that I read on this site.
I was talking about us folks that have to pass inspections to maintain our UL listings and limit our liabilities.
But as someone who spent many years welding (melting) steel and aluminum with 12-48 volts Ac and Dc, I would be hesitant to recommend these methods to people who claim not to know a rectifier from a thermometer.

Just do not want a fellow train guy or girls death or disfigurement on my conscience.
From experience having been hit with everything from 480 3phase to 60k back in the day when we still used core and coils to power neon, I can testify thy is not the voltage but the current that will get you.
Low voltage is not always as safe as novices want to believe.
Just MHO.

And I now have two documented cases of liste Chinese strip LEDs self igniting after being flexed and the onboard diodes/ resistors shorted.
Not minor flameouts but $100k damage to building facades and fire inspector and laboratory analysis by insurance investigators to show product flaws and not faulty wiring practices.

This is where my constant current lighting works well, being current limited also limits the amount of power dissipated to a very low level, even with a direct short.

 

BTW, there are no on-board diodes, other then the lights themselves.  I'd be interested to see exactly what the labs said happened...

 

Dale  H,Thanks for the offer i will certainly keep you in mind when i get to this project,could i use the accessory connections on the transformer for the hook up to the bridge rectifier?,i have several transformers i could use,i have a cw80,kw,110 watt type r. I have switched to the 180 watt power house to power each of the 4 loops that i will have,thats why i have plenty of extra transformers available.

You can vary the voltage of the CW-80 accessory output.

Dale  H, I see what you are saying now i cannot go over 12 volts without using more bridge rectifiers,& as Gunrunnerjohn said i could vary the voltage of the cw80 on the accessary taps ,which i have done in the past. I just went downstairs & adjusted the cw80 to exactly 12 volts on the accessary taps,the kw has 6,10,& 20 volt taps,i had not even thought about the CW80 until gunrunner john mentioned it, thanks John for bringing that up,i think that i will wait until i am ready to do this before i ask any more questions,but i really feel very confident that i will be able to do this ,thanks to all the help you guys have given me.

Dale  H ,you are right about there being a 14 volt tap on the kw,it was my mistake when i listed it as 10 volts.

I can testify that fffredd is definatly correct that its the CURRENT, not the voltage that will get you.  I once laying under a car, attempting to jump out a defective starter solonoid,  left hand on frame, right hand with screwdriver, in the dark, missed my mark and took the FULL hit of starter current.   It took a good minute for me to recover.    lessons learned the hard way,  i was lucky !!   Be careful people, its the CURRENT  !!