Temporary Lights

Another of my hobbies is keeping freshwater tropical fish. Ever since moving into my new house, and building my electronics lab upstairs, I haven’t been too interested in the fish. I give them more water when they need it, feed them on occassion, and do minimal basic maintainence.

The 55 gallon tank has gotten quite out of hand. A single variety of cryptocorne had gone on a killing spree, and had consumed the entire floor of the tank, wiping out every other plant that was in there. After it had consumed all there was to consume, fate turned the tides, and algae began to consume the crypts. So, with much disgust, I threw away all the crypts (mostly all covered with algae)… along with them went most of my substrate, entangled in the massively thick root balls of the crypts. So now my 55g sits empty – except for the fish, some huge snails, and the ugly life support equipment.

The tank normally has 108 watts of T5HO lighting (excessive for fw) , however, without any vegatative competition, algae would quickly rule the roost had I maintained normal lighting. So, I thought this would be a good application for LED lighting. The weak, sickly glow from “white” piranha leds will give me enough light to see my fish, and keep them accustomed to a day/night cycle, but not enough for algae to survive on.

piranha superflux LED strip

My solution involves 24 white piranha leds, with a color temp somewhere around 5000 kelvin. The 24 leds are broke up into four strips of six, those four strips wired in parallel across the power supply. The power supply is a LM317T wired up as a constant current regulator.

piranha superflux LED strip

The strips are designed with basic thermal management in mind. Since I am running the piranha at nearly 150mW, they generate a fair amount of heat. Therefore, I designed the strips with a maximum amount of copper possible, to act as heatsink and radiator.

pcb artwork superflux LED strip

All together, the ‘fixture’ consumes a little over 4 watts of energy. Here is the basic schematic of how things are wired up. This design is not very ‘safe’ … should an led strip fail as an open, the regulator will provide too much current to the remaining strips. The addition of a transistor and resistor to each strip would help combat this problem, by switching the current programming resistor in and out of the circuit… but this would require me to re-draw everything, make new PCBs, etc etc. This solution only needs to last a few months, once warmer weather arrives, I’ll be mail ordering some plants and have the tank restocked and the main lights working again.

superflux LED schematic diagram

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