Learning from one’s mistakes

After a number of failures with the other projects I’ve worked on recently, I was looking forward to a success with Project 3: LED Lights.

How hard can it be to wire up some LEDs? I’ve done it at least once before, so surely this project is the same thing – just with larger LEDs? Bash 3 LEDs into a parallel circuit with the bench power supply, add a fuse to stop things from exploding, jobs a good’un.

It turns out the fact they’re larger, is in fact, a complicating factor. Had I properly read the instructions in the book, I would have noticed the suggested wattage for the bulbs was between 2 and 10 watts. As the bulbs in question were 50-watt, and the maximum current my bench power supply can output is 5 amps, they were far too hungry for their own good, resulting in the ability to fully light one individual bulb at a time, but with vastly reduced light output when trying to attach two or more.

With a single bulb attached, setting the power supply to exactly 12.0 volts, I get a current draw of 4.23 amps. This is pretty bright and generates a lot of heat. I can increase the voltage up to 16.4 volts before the current maxes out at 5.07 amps, which makes the bulb even brighter, but equally even hotter.

Adding a second bulb to the mix results in 5.2 volts being the maximum the power supply can give before maxing out the current. The light output of the two bulbs together is vastly lower than the single, which I guess is a result of the reduced voltage. A third bulb maxes out at 3.1 volts.

I’m not too upset by this outcome, however, as I feel that I’ve learnt something. I think I understood there was a correlation between voltage and current before, but this outcome fully demonstrates it. I think – I’m still a bit iffy about it all.

It also helps demonstrate that, while a 50-watt bulb can produce a lot of light, it will also cause the battery to run out far quicker, so a balancing of your requirements and resources is always needed.

Anyway, this isn’t the end of this project, as I’ve just ordered some 10-watt MR16 bulbs. I’m hoping that, with them being 1/5th of the wattage, I should be able run 5 of them at maximum without any issues.

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