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The ultimate guide to building a minifridge into a 1998 Toyota Corolla
1-15-07
Introduction

It's a hot day. The bored weather man speaking through the static on the crackling radio tells you that it's 101 degrees outside. You kick yourself for using so many CFCs in your early childhood. Your butt is cemented with sweat to the interior of your car, and the air conditioner simply cannot keep up. Then, you open the armrest and take out a freezing cold beverage. "Thank god I built that mini fridge!" you say to yourself as you drive, worry free, down the interstate.

If you've ever wanted the ultimate James Bond car, this is the first step to getting there. For about $40 you can build yourself a minifridge into your car's armrest!.

How does it work?

This project is actually amazingly simple. It really consists of just three parts.

Peltier

The easiest way to make a minifridge is to use a thermoelectric or "Peltier" cooler. Essentially, a Peltier cooler is an electronic heat pump in that when supplied with a current, it pumps heat from one side of the plate to the other. When holding one, you might notice that once side gets extremely cold and the other gets extremely hot.


Here's a picture of the cooler I used.

Peltier coolers are very cheap. This baby cost me just under $15 on ebay with shipping. I used a 120 watt cooler. That's probably a little overkill for my fridge, but I can always put a dimmer switch on it if it gets too cold. If you don't feel like making a minifridge, Peltiers are a lot of fun to play with. Fun Fact: if you heat one side of a Peltier and cool the other, it actually generates current.

Heat sinks

Essentially, the point of the heat sinks is to move the heat through the Peltier as efficiently as possible. Heat sinks have are usually made out of aluminum or copper and have a bunch of fins which increase their surface area. More surface area = more efficient heat transfer. Both of these heat sinks have fans which move air through them and also aid in the transfer of heat.

One heat sink is actually a "cold" sink because it is used to suck the heat out of the inside of the fridge. I used an old intel heat sink I got off of an old Intel Pentium 2 slot processor.


Here is the Intel heat sink pictured without its fan.

The second heat sink moves the heat away from the Peltier and to the interior of the car. I figured this one should be bigger because if it's too small, the Peltier could over heat and eventually burn out.


Here's the second heat sink with its fan.

As you can see in the second picture, the heat sinks have a coating of thermal grease on their bottoms. Thermal grease can be picked up at your local PC store and is relatively cheap. It facilitates heat transfer by filling in the tiny crevices in the surfaces of the heat sinks and Peltier cooler.

Assembly

Here's the scary part. I happen to be insane, so I have no problem chopping up the interior of my car. I don't want to get horror stories about people destroying the interior of their cars in my inbox.

The armrest

The '98 Toyota Corolla's armrest has a small compartment underneath it. I figured this was the perfect place to put the fridge, and it actually worked out really well.


Here's the armrest

Here it is open.

First, I took out the carpeting on the bottom and cleaned all of the lint and dirt out of the compartment. This carpet might make a few convincing fake mustaches.

A quick test confirms that this thing can hold three sodas.
Destroying the car

To get better access to the compartment, I had to take off the top of the armrest. There are only two screws holding it on, but even after you remove those, you have to force it out of its place and I managed to crack part of the hinge in the process. This is nothing a little duct tape can't fix though.


Ouch!

Now we have a clear workspace.

In the back of the armrest is this pathetic little cup holder. When I got my car, it was already broken, but its cavity is the perfect size and place for the hot heat sink. So I broke it off.


It was actually really hard to get off. Oh yeah, and there's this brown goo everywhere in my car. Archeologists believe that there may have been a coffee incident sometime soon after the earth had cooled.

The hole is a perfect width, but a little too short.

A little hacksaw action, and it's good to go.

Now, I had to cut away at the inside. Originally, I was going to use a saw, but it was really hard to maneuver in the space, so a soldering iron with an old dirty tip did the trick.


Make sure the car is very well ventilated or you will die.

It's coming along nicely.

Done!

And the heat sink fits perfectly without any glue or anything!
Insulation

This is probably the easiest step of the project. You'll need to pick up some sort of insulation. I chose to use this insulation tape that they sell in the plumbing isle of Home Depot for wrapping heating pipes.


This roll was like $6.

Essentially, you just want to make sure the entire inside is covered. The tape is easy to cut with a pair of scissors for those oddly shaped spaces.

Here's the compartment completely covered. Make sure you don't forget to do the lid too.
Wiring

When wiring this minifridge, I decided that I wanted to be able to turn it on while the car was off. Keep in mind, that this drains the battery, so I don't recommend leaving it on for extended periods of time. The easiest way to wire this thing was to connect it straight to the battery. Keep in mind that this is not the safest way. In fact, it's very dangerous. A short somewhere in the project could start a rather unpleasant fire. It's probably a good idea to run it through the fuse box somehow, but I'm just lazy.


Just be careful when you do this. I don't want emails.

There's a small gap between the frame of the car, and the exterior. This connects the engine compartment to the door jamb.

This is really the only spot where you can see the wire at all, and it's covered when the door is closed.

Wiring this project is extremely easy. All parts use 12 volts which is just what a car battery supplies. Most fans will not spin when connected the wrong way, so just guess and check. Be VERY VERY careful while doing this, you do not want the positive and negative wires touching each other. It will make you die. As far as the Peltier goes, just guess and check again. The cool thing about Peltiers is that if you connect them backwards, they will just heat up the other side, so just connect it and make sure that the part on the inside is getting cold.

Finishing up

I don't have any pictures of the final steps, so you'll just have to use your imagination. I wired up both fans and the Peltier to the battery wires with wire nuts, then disconnected the wires from the battery so that the fans would stop.

As far as attaching the heat sinks to each other, I first made sure to put some insulation surrounding the Peltier on all sides, so that the hot heat sink would be better insulated from the cold one. To attach them tightly together, I simply worked a piece of stiff wire between the fins of the hot heat sink, then started to twist it on the side of the cold heat sink. I used a pair of needle nose pliers so I could really crank it down, and it definitely is not moving anywhere. When all that was done, I attached the fans and screwed the top of the armrest back on.


Here's a picture of the inside.

And here's the outside.
Modifications

Originally, the fridge didn't work too well, and was rather inconvenient. I still needed a switch to turn it off some time, and airflow on the inside was horrible. The problem with the airflow was that the inside heat sink was fit so tightly that the cold air had nowhere to go.

This was pretty easy to fix. All I had to do was make some slices in the fins to allow air to move around. I cut four slices with a hacksaw, and then broke the fins off with a pair of pliers.


Cutting aluminum fins with a hacksaw is really really loud.

I purchased a 12 volt 25 amp SPST switch from radio shack for about $3. Because I'm using a 120 watt cooler that uses 12 volts, I'm drawing about 10 amps, so a 25 amp switch is more than enough. The switch was designed to fit in a round hole and screw tightly into place. I melted a hole with the soldering iron and the switch fit in it nicely.


Notice the hole.

I drilled a hole as close to the bottom as possible so I could run the wires to the switch.

This switch is such a turn on.
Ouch

The fan on the back of the hot heat sink has no grill, so the fan blades are just spinning out in the open. I didn't really think much of this until, while testing the switch, my hand casually brushed up against the fan.


You should've seen the other guy.

Alas, my fan has broken, but this gives me an opportunity for an even cooler fan!

This minifridge is broadcast in HIGH DEFINITION!
Conclusion

The fridge works without a doubt. The only problem I'm having now is that the second fan was larger than the first, so it blocks a lot of the ventilation for the hot heat sink. Right now, the hot heat sink gets almost hot enough to burn skin. Because the Peltier can only maintain a 30 degree or so temperature difference, when the hot heat sink is so hot, the cold one can't really be that cold. I'm going to fix this by cutting holes in the sides of the armrest to allow hot air to escape easier.

If you chose to build yourself a minifridge, please send in some pictures, I'd love to see them.