Wall Warts

What voltage are the three LED strips rated for? I am assuming they have current limiting resistor(s) built into the strip, otherwise those LEDS will be short lived.

There are two wall wart types One type is regulated and can be a switcher topology or linear topology.  Either way they put out an exact voltage right up to their rated current output.

The second group is actually subdivided into two.  One sub group is just a transformer followed by a single diode or maybe a diode bridge, period.  The second sub group is the same as first except has one or two capacitors to smooth out the AC rectification ripple.  Only way to tell difference is either open up or use an oscilloscope to see lots of, or minimal ripple.   Finally the unregulated have an inverse current/voltage relationship.  Heavier current lowers the voltage and vice versa.

Leds don't care about ripple, as such, so capacitor no capacitor does not affect LEDs, usually (love these "weasel words").

Hope this helps or maybe confused you more .

Looks for regulated wall warts, they keep the voltage much closer to their ratings.

Unregulated wall warts are only at their rated voltage at their maximum current output.

Where can I find regulated wall warts.  There are rated for 12vdc, How can I run these off of accessory voltage which is 14vac

Thank You

Ken

I believe the LM2596 will work, I thought in a previous discussion there was another module but it had a meter on it showing the output voltage.  Can someone lead me in the right direct direction.

Thank You

Ken M

Forget the Walwarts,run the strips off the train transformer. Use an 18 volt tap and add a bridge rectifier and capacitor. That will give you a 24 VDC outlet. Wire the LED strips in series of 2.

Described in more detail here

LINK

Dale H

Ken, google "LM2596 AC-DC buck converter."  You should find them, to be ordered from China, for $3 or less each, including shipping, in lots of 5.

5pcs 24V AC/DC to DC 12V 5V,LM2596 AC DC Converter Step Down Module Power Supply, $13.20 with free shipping

Thanks, John.  Ken, Input these from your transformer; 14-18 volts should do.  Place a DC voltmeter on their output, and turn a small adjusting screw to set the output voltage you want.  The unit will hold this output voltage constant, unless of course the input voltage drops lower.  No need to spend the dollars for an onboard meter, set & forget works.

How many LED will this support?  The LED I have are Rextin 20 pieces w/3 LED per module.

Thank You

Ken M

You can get about an amp or amp and a half realistically from these supplies.  Trying for more power tends to get them pretty warm.  Given that you have 20ma loads for each 3/LED module, that's around 400ma, the module won't even break a sweat.

Thank You Very Much

Ken M

A nice find John

I ordered a few for adding miller signs to buildings. 

You say they get warm,do they use the same wattage as a regulator or resistor cutting down the voltage?

Once the output is set,would it vary with the input voltage or remain steady like a regulator? 

Does the adjusting screw for the output lock or can it change position from vibration? I was thinking for conventional passenger car lighting.

Dale H

How about using a HO dc power pack?

DaleH, a number of folks here have used that module for adding LED lighting to passenger cars.  A 22uh choke is added for DCS operation.

In fact, the Ebay seller in the link is the same one I used when I bought mine.

They don't use nearly the power that a linear supply would use, I can draw one amp out of one at 18 volts AC in and 12 volts DC out and it gets a little warm.  I have an LM317 based module with a big heatsink on it, the same test gets that sucker REALLY hot.   A switching power supply doesn't have to drop all the current like the Linear one does, it's more like a transformer as far as efficiency is concerned.

Dale H, this thread shows that module operated with conventional, variable voltage.  HTH.

Thanks John and guys for the information.

I read up on the circuit. Cant beat it for the price. Will use them instead of my 7805 when I do passenger cars. Will still stick with single LEDs. 

Dale H

John, if you're using the auction site AC/DC converter, where would you put the filter choke for DCS operation?

Thanks,

Rick

I expect grj to reply, but I installed his recommended 22uh choke on the left side of the input to the AC-DC LM2596 module as shown in a picture in this thread.

I would put it the hot feed.  The feed from the center rail.

If you're powering something from a wall-wart, you don't need a choke, that's only to isolate a track powered device from the track signal.  Since the hot side of this accessory never connects to the center rail, no choke necessary.