Led wiring

[mophius]

I have made the following diagram (very roughly) to help me understand, and then put into practice, simple wiring.
If I had a 9 volt supply and LED with forward voltage of 2.2 volts (6.6 volt total per series) i can then work out what resistance I would need to trim the circuit.
Am I correct in this diagram or should I go with something a bit simpler. I am more after the basics of the circuit than the amounts of LED's or voltages. I know if i exceed the forward voltage to overall voltage in a series then that circuit wouldn't work. I thought if I had a parallel series circuit as above then if one diode burns out or whatever then only that series would stop working. The other parallel circuits would still work and battery life prolonged.

sorry for the rambling, just want to get this right before starting to build a kit up.

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[slawton]

See if this makes sense for you...

You could treat each of the 6 parallel circuits as an individual circuit with it's own power supply of 9V and a resistor -- just how big a resistor? Well if you have 6.6V to turn on the current flow for the LEDs, then you need to have the resistor use the remaining voltage (9 - 6.6 = 2.4 V). Assuming you want the full current (typically 20mA = .02 A), you'd want a resistor calculated by R = V / I = 2.4 / .02 = 120 ohms. Any resistance value lower than this will cause too much current to flow through the LEDs, causing possible damage and burn out. Resistance values greater than this will reduce the current flow and dim the LED brightness. So you could use larger resistors if you want to lessen the brightness of the LEDs.

This would leave you with 6 chains, each with 3 LEDs and 1 resistor. Alternatively, you could have a single resistor in series (connected directly to the wire to the battery before it is split off into the 6 parallel branches). Since this resistor will have all the current from the 6 parallel branches (6 x 20mA = 120mA = .12 A), it would need to be 20 ohms (or greater). The benefit is you save 5 resistors, but there are drawbacks including LEDs may not be at the same brightness (due to variances in turn on voltages) and loss of 1 or more parallel branches would cause less current through the resistor (voltage reduced across resistor causing more voltage/current through the remaining parallel branches with possible LED damage/burn out).

[mophius]

I can see where the one resistor in the parallel circuit would be beneficial and in turn a pain when a problem occurs.
My diagram would be best desribed by saying that sets one, two and three would light the saucer. Sets four and five would light nacelles and set six light the secondary hull so having the two main wires going around the ship would be less of a problem but also I would have more components in the different parts of the build.

I know I cannot have all the resistors on a series circuit but cannot afford to have each individual LED have its own resistor for a single LED parallel circuit. My way of thinking was to incorporate the best of both circuits. I wouldn't want to have to take the whole thing apart to change all the LED's if one burnt out using the single resistor circuit.

I really need to find the time to wire up a circuit on the bench before I make any modelling decisions.

Can I just check also that the 30awg wire I have is man enough for this cuircuit or will i need something with a bit more beef to it?

[mophius]

Extending on from my former ramble, could one of the parallel sets of LED's have a different size or colours. Say for example a set of greens and then one with two larger red for bussards. All I would have to do is change the resistor to make the circuit correct.
That being said the bussards would be best off alone.

Ramble over