DIY chiller.

[tidioute06]

I've been designing a DIY chiller and I'm looking for a method to turn on a pump when the aquarium hits a certain high temp and turn it back off when it reaches the desired low temp. Anyone know anything that could accomplish this?

[DoctaQ]

what if you used a peltier unit to create a tiny bit of current to trigger some kind of signal. i totally made that up.
otherwise i think thermostats are very expensive

[wesknox]

Not sure what your budget or soldering/assembly skills are but here's a temp controller kit

http://www.mtmscientific.com/tempkit.html

You can extend the sensor with a piece of 2-wire cable (or twist 2 wires together and heat shrink...or whatever). Coat the sensor in something waterproof like non-conductive sensor-safe silicone (auto parts store), heat shrink tube...whatever). You'll need a power supply (a 12V 'wall wart', aka power adapter) and a source of 110V AC to plug that into, of course.

The relay on that kit will handle 120V AC but only to 1A. If your pump draws more power than that...two options. Wire up an external relay with higher current rating, or find another 12V primary relay with higher capacity contacts (many out there for cheap) and replace the one in the kit with the larger one. The higher-capacity relay likely won't fit the same holes as the one in the kit but a little creative use of epoxy, wires, and solder can fix that.

If you need more precision than this cheap kit (and well you might since you're dealing with just a few degrees between OK and "NEED COOLING", Doc's right, you're looking at some bucks to purchase this level of capability. This would probably be a digital programmable thermostat. Hardware stores used to carry "analog" temperature sensors with copper heat pipe-based temperature sensors (like a cooler or air-conditioner thermostat). These often had contacts rated sufficient to handle your pump, but copper and aquarium life don't tend to mix too well.

I have a Peltier module-based cooler on my list of projects (well down the list, though). I have access to some killer heat sinks from swap meets and HAM days which will dissipate a "ton" of heat! The CPU coolers I just used on my LED lighting are remarkably small and inexpensive and dissipate around 100W which (depending on the size of your tank) could do quite a bit of cooling. You might check those out to mount a Peltier module to (or to even use as a radiative cooling device).

Anyway, good luck with that project.

[wesknox]

Here's a find! This is a fairly sophisticated industrial grade temp controller with dual digital readout. It even describes applications as an aquarium temp controller...

http://www.auberins.com/index.php?main_page=product_info&cPath=1&products_id=1

The price is only $44.50. You'd need a thermocouple (they have one for <$6 that would need to be sealed/waterproofed) but are out of stock on a waterproof one for $26. Anyway, that's pretty cheap for the functionality it provides. Also, the switching capacity is far and above enough for just about any pump you're likely to use.

Whoa! Upon further review, the complexity of such an industrial temperature controller is likely to be overkill and unwieldy. Sure is cheap though.

[wesknox]

This is even cheaper still. It shows a relay that handles up to 10A at 120VAC. That should do it. The setpoint can be either to turn on cooling, or in heating mode to turn on heating (just like thermostat). Not sure about the pricision of the setting but it looks like it might work for you. For $15 and change, it's pretty inexpensive solution.

[tidioute06]

Thanks folks! these are some great options. I think I can make one of these work.

[Ajordan]

The Arduino platform is highly customizable but would probably require learning some new skills (that is a completely unfounded assumption, no offense meant).

this is one of many examples of what an arduino can do for aquarium control

http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1240000018

I was very intimidated by the very concept at first but I've started to dabble and I can say it's a great hobby that can compliment many others!

The PID controllers are pretty neat! That kit Wesknox linked also looks cool, glad I stopped in!

[wesknox]

AJ:

Thanks for posting that link. I have a working (but obsolete) Octopus 3000 and it lacks the kind of functionality that I'd like to have in a more flexible/modern controller. I'll definitely add a project like this to my project list for down the road.

W