Electric Car Heater

Circuit: Robert Dvoracek
e-Mail: imageimage
Home Page: http://beam.to/lightningstalker


If any of you drive a Civic, you know how long it can take for the engine to warm up; and if you live in the north like me, that's a prolonged torture ritual.  Necessity can be one mean mother.  This might just be a cure for those icy steering wheels and seats your butt freezes to in the morning.

The basic idea is to take an old toaster and an ATX power supply and bring them together in a sort of bizzare metalic mating ritual.  Okay, not quite like that.

Some of us have an old toaster that won't stay down.  A few of us have a computer power supply that went bad.  If you don't have either, there's a thrift store nearby that does.


SchematicAt this point, you may be asking yourself, "Why would I want to make a car heater when I could just order one from XXX?"  If so, you may also be saying other things like: "This is too dangerous," or, "Why does my diaper always get so soggy?"  If that's the case, then you should stop reading now and go back to Rachel Ray's site.  The wimpy car heaters that are sold in caltalogs barely put out enough heat to defog the windshield.  Our own custom heater can be scaled up to as many watts as we need.

Now that all of the babies have left, we can get started.  Clicking on the thumbnails at the right will bring up the full sized images.  First, gather up your raw materials which are:

Toaster with good heater wire
PC Power Supply (or 2. We need 2 finned heatsinks)
12V 30A Relay
12AWG Wire or heavier
30A In-Line Fuse Holder
Steel Springs
Insulated Standoffs

WireNow, there are parts from the toaster and the power supply we need to save.  The rest can be thrown away or stored for "future purposes."  In the toaster all we want is the heater wire.  The rest of the unit is prettymuch useless for this project.  Now from the computer power supply, we need the outer case, the fan, and 2 of the finned heatsinks.

With all the materials in hand, we can begin construction.  First we'll start with the heater wire because it's the trickiest part and sucks the most power.  What you want to do is wind it around the fins of the heat sinks and the ends of the springs so that it goes back and forth.  If you have a battery tab welder, you could also weld the wire to the heat sinks.  In a way, this is better because you don't need the springs to take up the slack due to thermal expansion.  The heat sinks should be mounted to the sides of the cover.  One is screwed directly to the housing.  The other is mounted on insulated standoffs to prevent short circuits.

In case you can't tell from the diagram, the power is switched by a relay that is controlled by a switch.  This allows us to use a smaller switch.  If you find a 30 amp switch that is fine; you can use that too; but I like the idea of controlling a lot of power with a small switch.

Heater in operation

For the fan, I found that when it runs at 12V it doesn't move enough air.  At 24V it seems enough; but the problem is that the car's electrical system doesn't run at 24V.  It runs at a bit more than half that, coming in around 13-14.4V.  So what to do?  You could buy a better fan, but if you're handy with a soldering iron and know how to read schematics, I've got a voltage doubling circuit that does the trick.

Now put all the guts in the old power supply box and connect the common relay terminal to the + terminal on the battery.  (the weak mail-order heaters connect through the cigarette lighter) Make sure the in-line fuse is connected as close to the battery as possible, prefereably on the battery.  The housing then connects to the car chassis.


Don't overload your alternator.

If you have any questions, my e-Mail is at the top of the page.

All drawings were made with XCircuit
, a platform independent, X-Windows application.

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