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Model Ship LED Project

vintorez1

Jan 2, 2017
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I have spent an entire day trying to piece together relevant information on how to light a model ship but all i can find are very basic and theoretical information. I would like to rig a fairly simple string of 6 LEDs from a 12V power supply.

Power Source: 12V computer power supply
Red LED: 2.1 V and 20mA
Red Flashing LED:2.1V and 20mA
Blue LED: 3.4V and 20mA
Blue Flashing LED: 3.4V and 20mA
White LED: 3.4V and 20mA
Green Flashing LED:3.4V and 20mA

A few questions.

By using a black and yellow wire combination on the computer power supply I get 12v. Since there are several black and yellow wires am I able to power multiple things that use 12v at the same time?

Since only my red leds have different forward voltage than the others can I rig 2 different series with one resistor for each series?

What the heck do you physically use as connections to connect multiple leds with their positive and negative wires and consolidate it into a single positive and negative wire that goes to the power supply? I've seen the whole science project with bare resistors and leds naked and exposed in series and parallel everywhere on the internet but no-one explains the practical application for connecting everything.
 

Gryd3

Jun 25, 2014
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Lucky you, all the LEDs you posted use the same current of 20mA.

The black and yellow wires on the power supply are usually all parallel to each other anyway... if you look on the board of the PSU, you will find all the yellow wires are bundled together and powered off the same spot of the board. Regardless of how that's wires, you can run as much as you want in parallel with 12V as long as the sum of their Current is less than the limit of the power supply.

You can certainly make as few or as many series strings as you want as long as you have a resistor on each string, and each string's SUM of forward voltages for the LEDs are below the power supply voltage you want to use.

If I were you, I'd get my hands on a female molex 4-pin connector (either stolen from an extension, splitter, or SATA power adaptor) to splice into my project. That way you can (un)plug your device whenever you want.
 

Bluejets

Oct 5, 2014
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What the heck do you physically use as connections to connect multiple leds with their positive and negative wires and consolidate it into a single positive and negative wire that goes to the power supply? I've seen the whole science project with bare resistors and leds naked and exposed in series and parallel everywhere on the internet but no-one explains the practical application for connecting everything.

I'm in to all sorts of model engineering and have at times used motor winding wire to connect LEDs etc.
Fine copper wire with varnish (or similar) insulation.

Reason being, one can hide the wire easily by cutting a slot into the wood or whatever.
Scrape off insulation with a sharp knife or burn off with a lighter and then scrape clean before soldering.

Also see one possible diagram for your connection as Gyrd suggested.
2 parallel circuits with the LEDs distributed evenly.
As he says, being all 20mA is a plus.
 

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vintorez1

Jan 2, 2017
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Thank you for suggesting the molex. I have a 4-pin molex with cpu fan connector. How does this setup look? 20170102_010312.jpg
 

vintorez1

Jan 2, 2017
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Sorry I was working on that picture for like 30 minutes trying to make it understandable :D

If I am looking at your picture correctly it is the same as mine but without the use of the 5v line and those leds incorporated into the 12v tie off. I was under the impression a series circuit had to have the same forward voltage for all the leds because only one resistor is used?
 

Harald Kapp

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I was under the impression a series circuit had to have the same forward voltage for all the leds because only one resistor is used?
That's not true. You sum up the forward voltages of all the LEDs in series, then use that to calculate the series resistor. Bluejets showes this in the calculations posted in post #3: 3 LEDs sum up to 8.9 V. That leaves 3.1 V for the series resistor.

Every series connection works that way: The voltage across the series circuit is the sum of the partial voltages across each element of the series circuit. The current through each element is the same and is the total current of the sries connection.
With a parallel connection the roles of voltages and currents are swappe: same voltage for all elements, total current is the sum of all partial currents.
 

duke37

Jan 9, 2011
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One way of connecting a wire to another is to wind a pigtale in one wire and to slip the other inside and solder. Use heat shrink tubing for insulation and neatness.
I use a small watchmaker's screwdriver as the former, it is strong enough to resist bending. I use this method to replace components in old valve radios using the dog ends of the old components.
 

Alec_t

Jul 7, 2015
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It's ok to connect the three non-flashing LEDs in series, with one current-limiting resistor, but I wonder if each flashing LED should have its own resistor and be individually connected to the 12V (or 5V) supply? The reason is that one turning off would turn off the other two if connected in series. Synchronised flashing may or may not be desirable or even possible (I've never used flashing LEDs) depending on the circuitry inside the flashing LED.
 

Harald Kapp

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I wonder if each flashing LED should have its own resistor and be individually connected to the 12V (or 5V) supply?
Once the flashing LED is off, it will drop the full supply voltage (12 V or 5 V), as without current (or a very small current for the flasher chip within the LED) there will be no or only a small voltage drop across the other elements in series. Check the datasheet of the flashing LED for max. voltage.
 

vintorez1

Jan 2, 2017
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Thank you all for answering my questions. I'll use the diagram bluejet suggested.
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Make sure you take note of the possible problem with the flashing LEDs.

At the very least, wire it up to test before you cut it to your model.
 

Bluejets

Oct 5, 2014
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Yes, I did think about that afterwards but you jumped on it before I could correct it.

Maybe this one should do...note you said you had access to the 5v as well.........
 

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