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MG Midget and Sprite Technical - ...and for my next trick - rear window heater

This is the sort of thing that only gets done in retirement! Back in the 1970s stick-on rear window heaters were popular. Not available now of course, except very expensively from the USA. So I made my own. It went through several iterations until I got it right.

First decision was the element. It's a piece of 30 SWG nichrome wire. I got the idea from an astronomy site - they wind it round lenses to stop them steaming up on cold nights. I had to calculate the right thickness and length. The substrate is 1.5 mm polycarbonate. The bus bars at the ends are brass strip from the model shop, stuck on with double-sided tape. The ends were left long for spade connectors.

I cut little slots in the ends and wound the wire snugly back and forth, ensuring good contacts with the bus bars. Now to stick it to the window. I tried various double-sided tapes, and the only one that worked was 3M 9088. It only comes in 50 m rolls! But I had to use 2 layers to allow for the thickness of the wire. The glass in the hard top is slightly curved vertically, hence the central strip of tape to hold the element to the glass.

The panel was wired up with 30A cable via a relay and bullet connectors at the o/s corner of the hard top. It draws 15A and only needs to be on for a few minutes to clear condensation. No frost yet since installation. I just have the ordinary dynamo which copes well with the load, even with headlights on.

Again, I'm not volunteering to make any more of this!

L B Rose

nice project, love your work!
Malcolm Le Chevalier

Nicely done!
Im intrigued by what kinda steeringwheel you have in that frog, any better photo's on the steeringwheel?
Arie

I fit one of these in a friends mini afew years ago think they still do them

http://www.ratsport.triumphshop.co.uk/onlinepurchase/ratsport/Images/partspics/RearWindowDemister/rearscreendemisterkit.jpg

mark 1500 on the road Preston Lancs

How do the front screen glass demisters used on some modern cars work? You cannot see any wires embedded in the glass. I presume that the laminate used has some electrical properties. Not that I am suggesting DIY possibilities here - just interested.
GuyW

No clue Guy, something of a heattransporting material in de glass or the laminated material I would guess.
I know Frontline sells them but sadly not in tinted glass.
Arie

I can see a mesh of TINY filaments embedded in the front windscreen of SWMBO's POS Ford. They're not easy to see, but they're there all right.

The manual says there are actually two elememts, driver's side and passenger side, supplied by two seperate fuses. Together they draw about 20 Amps. Yikes!

They come on automatically after the engine is started if the temperature is low enough, which seems to be 5 degrees C or below, then they're switched off either by a timer or thermostat, I can't tell which. I normally switch off manually if it's not really needed.

Perhaps there are cars that use some sort of conductive layer in the glass as Arie suggests, but if you have a really close look at most modern screens (from the inside looking out on a bright day) the filaments are just about visible.
Greybeard

Greybeard is correct. Ford do use elements embedded in the glass, although they are so fine you really struggle to see them. And he is also right about it being split in half. On my old Mondeo (now sold) half didn't work. Guess which half. That's right the driver's side!
Mike Howlett

If I was Prop - which I am not - I would be suggesting a heat exchanger wrapped around the exhaust/ silencer where it passes under the rear half of the car, feeding to an air duct powered by a ram effect from under the floor pan to blow warmed air up through a perforated tube fixed around the rear edge of the cockpit beneath the rear window. ;-0
GuyW

>>>Greybeard is correct. Ford do use elements embedded in the glass

As does my x-type Jaguar's windscreen.

I thought this was a fairly recent innovation, but when I was having a look round the HMS Belfast a couple of years back, I noticed that the windows in the bridge had heating elements embedded in the glass; the wire gauge and pitch looking very similar to the Jaguars. The HMS Belfast was decommissioned in 1963......

Jim
J Smith

Interesting about the Belfast, esp if the bridge windows are original.

But your X type owes a lot more than the windscreen to the Mondeo :-P

Nothing wrong with that - they're both good cars.
Greybeard

Arie, here is the steering wheel. The brand is Formula and it was on the car when I bought it in 1978.

L B Rose

This thread was discussed between 01/03/2016 and 13/03/2016

MG Midget and Sprite Technical index

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