Advice: Basic DC-LED circuit for stairs

[shockedmonkey]

Can I please get advice on the following 6 questions. I'm a lightweight - any advice is sincerely appreciated.

I want to put 12-VDC LEDs along my basement steps. I wired an outlet under my steps - wired as a 3-way w/ wall switches at top+bottom of stairs.
Q1: My outlet tester shows a very faint bit of amperage when my 3-way switches are off - the guy at Lowes says this is OK/normal? But is it OK for LEDs?

I bought a laptop-type AC/DC converter - 12VDC delivering 2.5Amps,
and some Eurostrips + Jumpers (Radio Shack calls these European Connectors).

I have 2 LEDs to try out. My plan is for 28 LEDs total (3 to 5 LED bulbs per LED-pkg). These are the step LEDs one sees all over the internet (3 or 5 LEDs in package, for motorcycles/cars).
3-LED light is 26-Milliamps, 5-LED is say 50 (or max 80-Milliamps).
So, my total amperage is between .7 and 2.2 Amps.

The LEDs don't seem to need any driver - people put these on motorcycles w/ no mention of an LED-driver needed. (Maybe no driver just shortens LED-life).

Q2: Will things work per my attached diagram? That simple?

Q3: Attached picture shows the AC/DC converter's device-end plug. I'll cut off this plug - but how do I tell which of 2 wires is the hot?
i.e. Does checking voltage/continuity work just 1 way or is it ambiguous if I have a fancy tester that may 'correct' automatically if I cross my 2 tester-sticks > Told you I'm clueless!

Q4: I assume my ground-wire ends within the AC/DC converter box, so I'll just skip any grounding?

Q5: I'll use 14-2 (low voltage) wire as needed?

Q6: I'll put Eurostrips, etc into a junction box. Am I within Code for this whole contraption?

Thank you for advice/help.

 

[kchriste]

A1: Since the LEDs are made for cars, they probably can be run directly from 12V. To be 100% sure, I'd need to see the datasheet. Can you post a link to where you bought them?
A2: Pretty much.
A3: We use the terms positive and negative when discussing DC. Hot and neutral is for AC. Most multimeters will tell you the polarity with a minus sign if the probes are reversed. You can probably get away with just trying the LEDs. If they don't work, then swap wires; again the datasheet would let us know if the LEDs can handle this.
A4: You probably don't have to worry about grounding. See A6 below.
A5: That is more than adequate. You could use wire as small as #18.
A6: I don't know where in this wide world you are located, so "code" is meaningless at this point.

 

[duffy]

That should work. Beware that the PIV on a white LED is only about 5V, so if you accidentally hook them up backwards, you could wreck them. Buy a cheap digital multimeter and be sure + is +.

"Code" with UL is only concerned with things over 50V, at 12V you just need to be careful not to short anything out.

 

[shockedmonkey]

Hey - its working!

kchriste / duffy -
Thank you for giving me confidence to proceed.

I wired-up 1 LED-light - and it works great!

Just as you said - if probes on my voltmeter are crossed, I got negatives. So, OK there.

Now I see the wires are incredibly small - Eurostrips and home-low-voltage wire are overkill. Will use the 18-gauge.

Re Datasheet?
Nothing exists so far as I know. Example link:
Extreme 5 LED STEP ACCENT LIGHTS with Blue LED
Search on "5 LED accent light" or "3 LED accent light" gets many links.

After I get the project done - I'll post a pic for closure.

Thank you.

 

[sgt-fig]

if u want the light to constanly on (like at the base of the hallway of the theatre) when the switch is on, you should use a paralle layout. connect a 1.2k ohms, 1/4 watt resistor at the positive end of the LED, the resistor brings down the voltage enough so it wont burn the LEDs. Connect the other end of the resistor to the positive of your source and the negative of the LED to the negative of the source repeat this for as long as you want, supplied power must be 12vdc any higher and you'll fry the LEDs, I have done this with up to 50 LEDs. If you want them to flash, find an LED flash sequencer circuit and adapt it to the idea.

 

[audioguru]

if u want the light to constanly on (like at the base of the hallway of the theatre) when the switch is on, you should use a paralle layout. connect a 1.2k ohms, 1/4 watt resistor at the positive end of the LED, the resistor brings down the voltage enough so it wont burn the LEDs. Connect the other end of the resistor to the positive of your source and the negative of the LED to the negative of the source repeat this for as long as you want, supplied power must be 12vdc any higher and you'll fry the LEDs, I have done this with up to 50 LEDs. If you want them to flash, find an LED flash sequencer circuit and adapt it to the idea.

What are you talking about?
A resistor in series with an LED does not "bring down the voltage". It limits the current so the LED does not instantly burn out.

Instead of properly calculating the value of the current-limiting resistor, you guessed wrong.
If the supply is 12V and the LED is a 3.5V blue or white one then for the lED to be pretty bright at 25mA the resistor value is (12V -3.5V)/25mA= 340 ohms. use 330 ohms for 26mA.

With your guessed resistor value of 2.2k then the LED would be very dim with only 4mA.