Simple electronics help

robfosters · 20 Jul 2015 at 15:48

im currently building my Millenium Falcon cockpit. I'm adding an LED driven fibre optic lighting system to it.

The top photo shows the LED circuit with a 9V battery attachment, and the bottom is a 4XAA power pack. What connection do I need to integrate the two so the LED's run off the power pack?

Diddums x · 20 Jul 2015 at 15:52

4xaa is max 6 volts, looks like you need 9 volts. I also don't see any drivers for the LEDs, you sure they're not little lamps?

robfosters · 20 Jul 2015 at 15:56

Deffo LED's and they do work. Already tried them with a 9V battery.

Can you buy a power pack like that one but one that takes a more powerful battery.

Diddums x · 20 Jul 2015 at 16:00

Yes of course. You can also grab the same kind of pack but for 6x AA in series, same effect.

robfosters · 20 Jul 2015 at 16:04

Diddums said:
Yes of course. You can also grab the same kind of pack but for 6x AA in series, same effect.

I didn't explain myself properly. I also need to run this 6 LED panel off the same power supply.

I am also planning on lighting the main hold, corridors, computer, dejarik table and the rear lights and ramp. Could end up needing to power around 20 3mm LED's. Gonna have to think a bit more about this one. It's probably going to end up as a mains PSU for that lot.

asim18 · 20 Jul 2015 at 16:05

Just search Google for "6 AA Battery Box" it's under £2 and comes with a standard 9V connection.

robfosters · 20 Jul 2015 at 16:08

Cheers, I'll do that. But I still need to know what connector I need to split it so that it can power more than one unit.

Diddums x · 20 Jul 2015 at 16:13

You any good at soldering? A simple solder joint and some heat shrink will sort you out perfectly. You could even make a mini wiring loom for added geekiness

robfosters · 20 Jul 2015 at 16:19

I have done a bit of soldering before, so I could give it a go. I'll wait until I have a more powerful batty pack though. maplins sell a 10AA one for 2 quid.

Diddums x · 20 Jul 2015 at 16:25

A 10 pack will either be 1.5v or 15v depending on if it's series or parallel. If you need exactly 9 volts, you need a 6 pack in series.

Diddums x · 20 Jul 2015 at 16:26

Just to clarify, AA batteries are 1.5v, hence the numbers

robfosters · 20 Jul 2015 at 16:29

How do you know what voltage an LED needs?

firstborn · 20 Jul 2015 at 16:33

Diddums said:
4xaa is max 6 volts, looks like you need 9 volts. I also don't see any drivers for the LEDs, you sure they're not little lamps?

What's a 'driver' for an LED?

firstborn · 20 Jul 2015 at 16:34

robfosters said:
im currently building my Millenium Falcon cockpit. I'm adding an LED driven fibre optic lighting system to it.

The top photo shows the LED circuit with a 9V battery attachment, and the bottom is a 4XAA power pack. What connection do I need to integrate the two so the LED's run off the power pack?

How's the build going - I haven't started putting mine together yet.

Diddums x · 20 Jul 2015 at 16:38

robfosters said:
How do you know what voltage an LED needs?

It would be on the packaging usually. If you've butchered them from elsewhere, then the same as what they were using before.

Firstborn: for some reason I can't paste on my phone, search "future electronics led driver". Pretty good explanation, but I don't think these will need one.

Burnsy2023 · 20 Jul 2015 at 16:48

firstborn said:
What's a 'driver' for an LED?

Normally you'd have a simple transistor and resistor circuit used to light an LED.

robfosters · 20 Jul 2015 at 16:55

firstborn said:
How's the build going - I haven't started putting mine together yet.

Only just started myself.

I like waiting for at least 20 issues before starting. Gives me time to see what others are doing and any problems they have found and how to overcome them. For example, the gun turret is positioned wrong.

Thekwango · 20 Jul 2015 at 16:57

Diddums said:
It would be on the packaging usually. If you've butchered them from elsewhere, then the same as what they were using before.

most any packs of leds I've bought never had voltages marked on them - though to be fair I was buying cheap packs of 50/100 from the bay

iirc different coloured leds require different voltages. been a while since I tinkered with leds so could be wrong. was sure though that I used to have a little chart that showed max and typical voltages for the different colours

Tealc · 20 Jul 2015 at 17:24

What's in that heatshrink area on the left of the first picture? I wonder if it is a power resistor that acts as a very crude LED driver in this assembly. Those LEDs look like they are wired in parallel so theoretically a 6v source would work but at a lower luminance than a 9v battery would allow.

Based on the LED PCB and the 330 Ohm resistors you'd likely be better with 9v for that one too.

All together with wiring harness and PCB assembly you'd looking at drawing around 200mA at 9v, or around 1.6W. You'd drain a 9v battery in around 2-3 hours. This is based on 330 Ohm resistors and white 20mA nominal LEDs.

It could be that the wiring assembly has a much higher value resistor so you get a low amount of light. The amount of light off that PCB at 9v will be really quite bright.

firstborn · 20 Jul 2015 at 17:26

A LED will have a max current (I) rating and a fwd voltage drop when on (VL). A current limiting resistor (R ohms), in series with supply and LED, is required to ensure the max current rating isn't exceeded.

If your supply voltage is VS, you need to drop (VS-VL) across the resistor. Therefore from Ohms law R = (VS-VL)/I.

You only need a series resistor to limit the current, nothing else needed to 'drive' the LED except something to switch it on and off, could be a mechanical switch