Wednesday, 17 October 2012

Fish Tank Disaster

Relax it's not as bad as it sounds...

Those of you who have ever been to our house will know that we have a growing collection of fish tanks present in our lounge room.  The second largest tank is an AquaOne AR-980 - which looks something like this :

The top of the tank is covered by a plastic hood (ours is black) that contains 3 individually switched fluorescent tubes, behind a plastic cover.  As you may expect from a tropical fish tank, there is quite a bit of moisture about the place, and cheap-ish electronics and water tend not to mix very well!

In May 2012, we noticed a rather strong burning smell coming from the lounge room, which we fairly quickly traced to the fish tank hood.  One of the fluorescent ballasts had become very hot, and was in fact starting to smoke. The ballast has since been removed, and we continued on with just two lights instead of three.

Then in October 2012 we noticed another burning smell, and found that the ballast on one of the other lights was going the same way as its sibling.  We haven't been game enough to turn on the third light any more!  So - no more fish tank lights for the time being.  The fish themselves get enough light from the room, but the plants in the tank are not going to be happy for long without their daily dose of light.  So the decision came down to - replace the whole hood (expensive - and likely to lead to the same problem in  a year or two), replace the ballasts (if I can find one - and again, likely to fail again in a few years) or go the DIY hacker route and replace them with LED lights, and a custom controller.

Of course you can guess route I've chosen!

To work out if this is even feasible with LEDs first I looked at the specs of the current tubes
The tubes are :

1x Atman 15000K 25W tube
2x Atman 8000K 30W tube

Using a value for tubes of 60 Lumens per Watt, that gives us

1500 Lumens at 15000K (pink/violet light)
3600 Lumens at 8000K (cool white)

We rarely have all three lights on at once, so these can be taken as a maximum requirement, and not a 'must have'.

I've considered two options for the LEDs - either using a small number of high per LEDs (such as the Cree 1W or 3W Star LEDS) or using a large number of smaller LEDs in a strip configuration.

The high power LEDs are probably more efficient, but they require a bit of work in heatsinking, and possibly active cooling such as a fan, or even running piped aquarium water through a heat exchanger, which I've seen somewhere (hack a day maybe?)  The hood does contain a sheet metal plate that the tubes were mounted on, so that may be sufficent heatsink, but again I'm worried about water ingress due to condensation, which is probably what killed the original ballasts.

Some eBay research shows that the Cree 3W (nominal) Q5 LEDs can produce 107 Lumens when driven at 1.2W, and up to 228 Lumens when driven at 4 Watts.  Guesstimating at 200 Lumens when driven at 3 Watts, that means I would need 18 to give me my 3600 Lumens of cool-white light, for a consumption of 36 Watts.  (Noticeably less than the 60 Watts that the tubes would use)

The LED strip lights can be bought in waterproof strips, and because they are more distributed, the heatsinking isn't as much of an issue.  There are two types of LED strip out there, one uses the 3528 SMD LEDs, the other uses the larger 5050 LEDs.

3528 LEDs produce about 4 Lumens each - so a 5m 300 LED strip gives me about 1200 Lumens.  They do come in 600 LED strips too, which would give me 2400 Lumens for 48 Watts.

The 5050 LED strips give me about 780-900 Lumens per meter, so 4000 Lumens for a 5 metre strip.  A 5 metre strip uses about 72W when driven fully.

I was able to pick one up on ebay : for about $16.

That takes care of the main light, additionally I'd like to have a little extra light when showing off the tank, and a blue 'moonlight' to use at night.  A strip or two of the 5050 RGB strip will take care of this - I can use it to add some tint to the colour during the day (additional red and blue to help the plants), or just run it as blue at night.

The strips of course need some supporting hardware - the white strip will need 12V 6A (72W) at full power, and  a metre of two of the RGB strip will require another Amp per meter.

To control 6A,  PWM is the only way to go - so I've purchased a cheap PWM dimmer that can handle up to 8A.  The RGB strip comes with its own small controller that lets you dial up any colour, so I'll be using that as well.

That's enough to solve my immediate problem of no light in the fish tank.

Stage 2 is where it gets more interesting - and I'll write about that in the next post.

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