I use a heater like this in my Instructable on making perfect steaks. I hook it to my themostat control project to maintain the temp.

Out of the box these heaters have a limit of about 90 degrees F. That's good for live fish, but I wanted to be able to hold water in a cooler at up to 150 degrees F. A computer controller immersion heater is $200+. A thermal probe and an aquarium heater are $60 or less.

This Instructable will show you how I did it.

1. Always use your head. House current, water and glass are involved. Lots of ways to get hurt.
2. Always keep stuff unplugged when you are working on it.
3. Read the warnings on the heater before you void the warranty.
4. Never dunk a hot heater into water. The glass will shatter.
5. Always use a GFCI outlet.

Step 1: Gather Materials

You won't need much.

1. An aquarium heater.*  Mine is 30 watt and works easily in 10 gallons+ of water.
2. A few towels to hold the tube or maybe soak up the blood if you get too rough.
3. A pair of needle nose pliers.

A soldering Iron and solder.

*Get a new one! If you can see coils of wire inside, it's the old style. I would not mess with that kind.

Step 2: Remove the Control Knob.

Unscrew the control knob. Mine had a catch to prevent you turning it up past 90 degrees. I had to wiggle it and use a little force. Nothing drastic though.

You can remove and discard the collar that was making it hard to unscrew the control knob. It will just be in the way from now on.

Step 3: Remove the Plug.

This is the most difficult step. Go slow. Take your time. Be careful.

Wrap the tube in the towel. This will protect your hand if something goes wrong and you shatter the glass.

Using the pliers, grab the plug. Put one end in the hole and the other end on the edge of the plug. Slowly work the plug out. Try not to tear the rubber, or pull on the cord.

Once you get the plug most of the way out, slow down and pay attention. The heating pad will come out and you will need to get it back in. Mine had a foam insert that was wrapped around a plastic tube.

Step 4: Hack the Switch

There will be a metal strip that pushes the button on and off. I just bent the metal strip until it was always firmly pushing the switch. Even when I hit it with a heat source over 150 degrees F. (heat gun or blow dryer.)

Optionally you can remove the switch and solder the leads. I was afraid of melting the plastic heater part.

Step 5: Put It All Back Together.

This is almost as hard as getting the plug out. Go slow. Don't push too hard. Be careful of the glass tube.

Roll up the actual heating element around the foam the way it was in the first place. Gently put the heating element back in the tube.

You can lightly lube the plug with some machine oil. Gently but firmly start working the plug back into the tube. Don't worry if the last bit doesn't want to go in. It will still be waterproof if you get it most of the way.

Screw the control stem back in to finish the waterproofing.

Your heater is ready to use. To cook my steaks, I just plugged in the heater when the temperature started to drop, and unplugged it when it got high enough.

You could also make a micro-controller powered outlet and hook a thermostat of some kind to it.
<p>30w is getting you to sous vide temps? I was planning on needing 100w minimum, possibly 200w to cook ~10lbs of chicken in a 5gal cooler </p>
The answer is &quot;Eventually&quot;. In a decently insulated vessel 30w can shift the temperature surprisingly fast. That said, with this setup I usually heat the water by other means before adding it to the cooler. You can fill it with cold water and then bring it up to 140-150F easily with a pot of boiling water from the stove. I have also just filled it with 110F water from the hot water in the sink and let the heater bring it up over the course of an hour or so.<br><br>If you want to heat the water quickly, you need a much bigger heater. I have cooked 20+lbs of meat in a large cooler with nothing but this heater and it was off more than it was on. It puts out plenty of energy really. If your vessel is not well insulated you might be losing heat faster than this would replace it but you would have to have really bad insulation and put it in a cold place. Even just wrapping some towels around a pot should work fine.
<p>I went ahead and tried it with a 300w heater. Your hacking mod works great, but 300w is still painfully slow to heat up. The water I started with was ~135 degrees, it took over 2 hours to get from there to the set temp of 148. I know I can ad water from the stove to help, and I'm also considering jumping to a 600w+ immersion heater instead of the aquarium heater.</p><p>Once it gets to the target temp, the cooler/heater combo holds is very well. I saw less than 0.3 degrees fluctuation.</p>
<p>Thanks for the &quot;hack&quot;. I have tested &quot;sous-vide on a budget&quot; for a couple of times now, a medium big casserole, the tenderloin in a thick zip bag, and a decent thermometer. Just adding a bit of boiling watar when the temp goes down, try keeping it on 131 degress F...Works pretty good:</p><p>But now i'm reade for step 2, I have got a small USB pump to circulate water aprox $ 3-4, waiting on a USB Heater, but my sources say it will stop att 113 degress F. So when I get it I will try with your idea to modify it. I will probably need 2-3 more of these, because thea are on only 8 watts each.</p><p>The main thing is to run it on USB, no high voltage involved. Everything ordered from china and will end up on about $ 10 - 15.</p>
<p>Have you experienced any degradation of the heater due to operating at much higher temperatures than an aquarium presents? Have you run it up to 190F and held for a extended time to see of anything gets soft or falls apart due to the heat? I would worry that this type of heater may not be designed to operate at sous vide temperatures, especially at the high end, near boiling water temperature. BTW: Nice idea. I'm thinking of a couple of 300 watt heaters like this (about $6 each on ebay), with a small RC boat propeller (about a buck on ebay) and a small DC motor (out of the water) to make a system with a circulator in a 24-quart cooler. That would be big enough for very large cuts of meat.</p>

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