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Topic: Small heater (Read 2664 times) previous topic - next topic

bvbellomo

I am building an Arduino controller for an aquarium light inside an enclosed canopy.  When the lights go out, the inside gets a lot of condensation.  I am looking for a small, fanless heater that can be controlled by an Arduino to heat a 24" x 48" sheet of aluminum.  I suppose I could rig up something just with Nichrome wire, or even just add really inefficient lights, but I bet they make something that is a good fit.

MarkT

#1
Mar 03, 2015, 01:56 am Last Edit: Mar 03, 2015, 01:57 am by MarkT
Bolt on power resistor.  What's your supply voltage and how many watts do you think
you need?
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

weedpharma

#2
Mar 03, 2015, 02:05 am Last Edit: Mar 03, 2015, 02:06 am by weedpharma
Google "aluminium clad resistors".

Spread a few over the plate to spread the heat.

Work out how much R you need using Ohms law.

Weedpharma

bvbellomo

That's exactly what I need!  Thanks!

I have no idea how to size what I need.  A small increase in temperature to the aluminum should be enough to prevent condensation, but the whole thing is made to dissipate heat.

Do you think it would be stupider to try to use 110 Volts A/C directly, given the amount of salt, water and aluminum involved and potential to short out?  Or would it be stupider to transform this first, probably to DC, even though I am only using it to generate heat?

weedpharma

Definite no to mains power.

If you require say 12 watts, you need 12v and 1A. To get 1A, you need 12 ohms. To get this R in 3 Rs, you need 3 x 33 ohms (wired in parallel equals 11 ohms) each will need to be rated at 5W.

You could also wire the Rs in series but would need 3 x 4.7 ohm.

Note the values for the Rs are values that you can readily buy.

You may not need as much power but you the method above and ohms law to work out the Rs required at the heating you select.

With the salt air, you will need to protect the electrical parts to avoid corrosion.

Weedpharma

bvbellomo

I understand the math, but have no idea if I need 1/3 of a watt, 3 watts, 30 watts or 300 watts of heat.  Although I do know 300 watts (the lights) does prevent condensation.

If I don't use mains, what power source should I use?  The final design will use 2 separate DC 54 volt sources rated to 6 amps, but I'd rather just add a heater off a wall-wart or something to prove the concept before I deal with arduino errors sending 300 watts through the resistor or shorting out.  Any efficient power source over 10 watts starts getting expensive.

Why would I use more than 1 resistor?  I'd assume just heating 1 corner would heat the whole sheet as well as heating all 4.

jremington

Trial and error works when you don't know how much power will be required. Start small and move up.
You can get 10-40 watt power bricks for nearly nothing at thrift shops.

Chagrin

You might also consider heated plates used with 3D printers. They're not particularly expensive (check eBay) compared to aluminum clad resistors and would spread the heat out pretty well. They're a bit overpowered for just keeping things above the dew point but you can use a 5V supply or such to keep the amperage low.

Also, the obvious choice for an inexpensive power supply would be an ATX power supply.

MarkT

No need to spread the resistors out if the aluminium plate is thick enough, its a great
conductor of heat itself.

For mains heating use a mains heater designed for aquariums, otherwise you are
creating a real hazard.  A mains transformer used to power a 12V halogen bulb is
a good option - nice safe voltage and available for several power levels.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

TomGeorge

Hi,

Is the aquarium heated?


You may be better fitting a small computer fan to circulate fresh air in one end through the light canopy and out through vents in the other end.
It will not need to be a great air flow, so a CPU fan, nice and quiet would probably do the trick.

Heating will not get rid of the humid air, only prevent it from condensing, I think you will find corrosion will still occur.
A fan will probably consume less power and purge the damp air.
Very humid damp air will conduct, you didn't say what voltage you lights are?

Tom...... :)
Everything runs on smoke, let the smoke out, it stops running....

MarkT

A fan will chill the aquarium though....
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

TomGeorge

Hi, 
How else do you get rid of humid air?
You are going to use energy to heat the air in the top with resistors, against heating the tank (if it is heated, we don't know yet) a little harder to compensate for fan cooling, 6 of one, half a dozen of the other.
Fan does not need to blow a gale.
Aquarium lights that I have seen have vents in them anyway and let heat out.

Tom...... :)
Everything runs on smoke, let the smoke out, it stops running....

Chagrin

How else do you get rid of humid air?
Might consider a peltier as well. It would have the advantage of keeping the aluminum plate warm and creating a point of condensation, returning that humidity back to the tank.

bvbellomo

I've had a saltwater tank since 2001, so I've been doing this a long time.  I haven't seen a commercial canopy for a coral tank without a fan, and most of them have glass or plastic to protect the lights.  This is the conventional solution, but it has some major drawbacks:

1) The fan removes humidity.  This lowers both the water level and temperature of the tank, and raises the humidity of the house or requires an outside vent be installed.  With a 20 gallon tank, this is a non-issue.  With a 200+ gallon tank, that is a lot of water.  Even if I could vent outside, I still have to replace evaporation with RO water.  I pay to heat the tank, even in the summer.  Before LEDs, most people ran chillers, so cooling was a plus.  This is actually one of the major limitations against owning a very large (1000 gallons or more) tank.

2) The fan makes noise, which is unwelcome when trying to relax and watch the fish.

3) This is another electrical component that corrodes, fails, and needs replacing.

With Metal Halide lighting, no one thought seriously about passive cooling.  However with LED, I believe it is possible to do without a fan, but I understand this is not conventional.

bvbellomo

A Peltier device is an interesting idea.  Any idea where I might get one that would work?

As far as a power source, I don't know where you live that has thrift stores with power bricks, but around here the closest thing they sell are sewing supplies and VHS movies.  Even the local Radio Shacks are gone.  I have an old 15volt 1200ma brick (probably too small), and some constant current meanwell LED drivers (HLN-80-36B and LPF-40D-54).  Do you think it is safe to use a LED driver for this?  Once I find the right size, I might buy something cheaper to reuse or resell my LED drivers.

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