Need help/advice - USB heater

[skocko76]

Hello all! I'm new to this forum!

I need help concerning alteration of an USB gadget.
I have a small (2.5dl or 8.5 fl oz) USB aquarium that I intend to use to raise sea monkies (artemia).
The gadget was advertised to heat water up to 30C (86F) which it doesn't.
The best it does is to keep a 4C difference from room temperature. As the room temperature goes down, so does the water temperature. Needles to say, the water temperature is too low and too unstable to grow sea monkeys.
I would like to replace the inadequate heater with a stronger one keeping in mind the usb voltage and all that. The heater looks like a block of white foam covered by a thin aluminum foil.
Could you please suggest me an electronic element (resistor, what not) that I can replace the heater with and get better results?
I included pictures of the gadget and the heater.

Thank you so very much!

 

[ARandomOWl]

The maximum current drain from a USB port is 500mA (with a registered device). This is at 5V giving you 2.5W to work with. 1W is the power required to increase the temperature of 1L of water by 1 degree centigrade (hope I got that right).

In other words, your USB port can't provide a lot of energy to heat the water. To keep the water temperature stable you would need a "thermostat" to switch the heater on and off.

 

[MikeMl]

An aquarium heater is >50W. I'm guessing you will need >15W

 

[ARandomOWl]

Hmm I got things a bit mixed up before. It takes 4.2KJ to increase the temperature of 1L of water by 1 degree centigrade. Either way, the point is the limiting factor is the power provided by the USB port, not the circuitry connected to it.

 

[Sceadwian]

This is eight ounces of water we're talking about, and the amount of energy required to heat a volume of material to a certain point has to take into account the heat transfer characteristics of the materials and the environment involved. That being said even under optimal conditions 2.5watts for maintaining that temperture in a normal environment is probably not gonna happen. I'd guess close to 7-10 watts. So you either need tot use more USB ports, or do something inteligent and supply it power external to the system. The 'cool' factor of a usb powered fish tank is totally shot down by practical factor that it's going to end up stressing a power supply designed to power data devices....

 

[skocko76]

Thank you all for quick replies.
Looks like I'm stuck.
I know nothing about electronics so I have yet another question:

Quote: "So you either need to use more USB ports, or do something inteligent and supply it power external to the system."
Suppose I use another usb port to power the heater. I suppose it's the wrong way to simply solder another usb port's wires to heater's anode and cathode. That would backfire, right? Is there a simple way to add power to the heater?
The power that it's currently getting is thermostat controlled. I assume that if i bring in another uncontrolled power line it wouldn't overheat as it is weak as it is. The remaining thermostat controlled power line would then control the temperature of the water. Or am I just talking nonsence ?

 

[Reloadron]

Strictly my take but do not use a USB port to get the heater power. USB ports are not very forgiving and one small boo boo and bad things can happen.

If you absolutely want to heat something using always on computer power consider using the 5 Volt SB (Stand By) power from the system which should give you an amp at least depending on what the system uses or get an external heater and power supply.

Just My Take
Ron

 

[KeepItSimpleStupid]

Way back when, I saw an article about making an aquarium heater. They took a bunch of resistors in parallel and ran two wires to it and covered it with aquarium friendly RTV and burried the heater under the gravel. You can pick any safe voltage like 12V. 12 Watts would be 1 AMP. The toatl R would have to 12 ohms. You just have to solve 1/Rt= 1/(1/r1+1/r2+1/r3...) Intuitively: Two 24 ohm resistors in parallel would be 12 ohms. Four 48 ohms would be 12 ohms as well. Eight 2 watt 100 ohm resistors should be close to a 16 W element and 12.5 ohms. Wire would would be a good choice for type. Rt=1(8*1/12). The maximum permitable wattage adds. 8 * 2W = 16 W. P=(V^2)/R and that's what's limiting power in this case.
=(12V^2)/12.5 or 11.52 watts.

Now all you have to do is see if 11.52 W is enough power, and a temperature sensing element and build a simple temperature controller. Actually the voltage would be slightly less too because of drops in the final control element.