Electric PTC Heater

This mod was done mainly as an experiment, since I've not seen it done elsewhere. The Defender heater in the Ibex works very well, since the Ibex is left draughty than many Land Rovers, but tdi engined vehicles take a while to warm up, so demisting the screen can be a problem for the first few miles of a journey in the wintertime. No problem with a Webasto fuel burning heater, but that requires forward planning.

With modern diesel being so efficient, many vehicles are now fitted with PTC heaters to assist with demisting the screen. PTC heaters are clever devices, made from a ceramic material with a metallised coating. What makes them clever is that their resistance rises rapidly at a particular temperature, fixed at manufacture. When power is applied they can draw a large current and heat rapidly to the design temperature, then reduce current draw to maintain the temperature. As more cooling air is passed over the device, the current drain increases to maintain the device temperature.

Regular ebay searches turned up a heater module in good condition, for an unusually low price, presumably because one of it's wires had been cut. Since I don't own a Peugeot 807 or whatever this came from, this is not a problem! I had no idea if the module was a suitable size, but the price was good enough to make it worth a chance.


Examining the unit showed the heater is broken into 3 parallel sections, each of which draws around 30A on startup, dropping after a few seconds as the temperature rises. In total this 90A draw rates the heater at just over 1kW (!) That's not particularly a problem to operate, but it does require some care, both in the wiring installation to prevent a fire risk, and in operation to prevent an unexpected flat battery.

Measuring the heater module against a spare Defender heater box showed it to be almost exactly the right size and shape to replace the 'on/off' heater door at the point where the heater box blows into the dashboard. (Since the cable to operate that door on the ibex siezed up and broke about 5 years ago, it seems I am unlikely to miss it.)

The heater turns out to be slightly (~15mm) too long to fit into the box nicely, so an ideal opportunity to break out the CNC mill and make a couple of mounting brackets to take up the gaps.


A bit of careful measuring and cutting, and the module fits nicely into the exit airflow.


Cutouts each side of the heater box.



Brackets are glued on with instant gasket and screwed in place.


To keep the high current wiring as simple as possible, the relay is mounted directly to the heater box.

(Albright solenoid conservatively rated at 80A continuous duty.)

To complete the installation, a high current earth strap return to the chassis, and the main power feed comes from the underbonnet fusebox - a high current type which replaced the standard Defender item. Since the Ibex has no rear screen demister, the switch and warning light seemed ideal to use to trigger the electric heater.

I saw no need to have selectable heat levels, so I simply wired up all the elements in parallel. If this turns out to be overkill (unlikely), I can simply disconnect 1 or 2 elements at a later date.


Proper results will have to wait for less pleasant weather, but a quick test on a warm day had noticeably warm air at the windscreen within 30 seconds of switch-on, with the fan running at full speed.

Current draw stabilised around 47A, though this would be higher with colder inlet air temperature.

NC Data for the mounts I made are available here. A demo version of CAMBAM will be needed to view the source drawings.