heated rear screen

Post by **246gts** » Sun Dec 18, 2005 4:29 pm

I have got a second hand heated rear screen for the Minor saloon.
Decided to try to test it before fitting so I have connected my battery charger across it and taken readings across the terminals at either side of the screen with multimeter.
With no load other than a hand lamp the battery charger is reading 10 volts, connected across the screen heater element I am reading 6 volts.
This tells me two things
the screen element must be intact to get any circuit
the loss in potential is because of the resistance of the screen element
It is a long, long time since physics O-level so can any of you tell me if this reading sounds about correct?
Dave

Post by **bmcecosse** » Sun Dec 18, 2005 4:58 pm

Yes - sounds ok - but the charger should show more than 12 volts off load, or it will never charge a 12volt battery. Is this thing to keep your hands warm - when push starting the car ?

Post by **ColinP** » Mon Dec 19, 2005 3:12 pm

Dave,

it sounds ([pedant mode on] ok, it reads [pedant mode off]) as if your battery charger is a low wattage one (3-4 amps max) designed for trickle charging.

The internals of this will prevent you drawing too much current, so the voltage drops as well.

All the best,

Colin
p.s. do you have an alternator?[/quote]

Post by **Cam** » Mon Dec 19, 2005 3:13 pm

Yep, the battery charger can't supply the current for the heated screen so the voltage dips. Don't connect it for too long or you might damage the charger.

But it sounds ok. Try it on a battery for a more accurate reading.

Post by **ColinP** » Mon Dec 19, 2005 3:14 pm

Snap!

Post by **Cam** » Mon Dec 19, 2005 3:16 pm

Post by **246gts** » Mon Dec 19, 2005 8:41 pm

thanks all,
I just use that old battery charger to power a hand lamp and it is a convenient source for dc on my bench. Anyway it appears that the element is completing the circuit so lets hope it works. Next two problems are getting the glass into the car and then wiring up the circuit
Dave

Post by **Peetee** » Mon Dec 19, 2005 11:09 pm

Next two problems are getting the glass into the car

A four handed job for sure - and not something I would recommend doing in a cold environment. The rear screen rubber needs to be very flexible, ie warm. And use some parcel string coated in candle or waterproofing wax.

Post by **Gareth** » Tue Dec 20, 2005 6:44 pm

Even better... get autoglass to do it - if it breaks, are they not liable??

Post by **bmcecosse** » Tue Dec 20, 2005 11:02 pm

Not unless they supplied it! I would say get a new rubber before attempting this - most of my exeperience on window fitting is with Minis- and it's almost impossible unless using a new rubber, and sealing strip.

Post by **Cam** » Wed Dec 21, 2005 10:55 am

I think they ARE liable as I think Turbominor (Iain) had them fit his windscreen and they cracked one (splitscreen) fitting it, so they supplied another free of charge if I remember correctly.

Post by **246gts** » Wed Dec 21, 2005 1:18 pm

Everyone I speak to about fitting glass says use string! I assume that the string is put inside the recess in the rubber and in the process of getting the rubber to fit over the projecting edge of the body you pull the string out gradually to make the rubber flip out over the body.
Pardon my ignorance but exactly what do you do with the string??
Dave

Post by **ColinP** » Wed Dec 21, 2005 2:40 pm

Dave,

The way I remember (non Moggie - so the easiest method may be a little different):

The rubber was fitted to the bodywork, and the string put into the channel where the glass was going to be. You then place the glass against the rubber and by pulling the string, the rubber lip is pulled out and over the screen edge. That's why the string should be smooth (not hairy - as I found out), and lubricated so it doesn't tear the rubber and comes out easily.

Also that's the 2 person/4 hands bit - unless you're blessed with additional limbs

I'm sure someone's done it the other way (glass first)

Colin

oh yes, and I believe the fitter is laible if he damages your property (maybe Scots law is different

)

Post by **Alec** » Wed Dec 21, 2005 6:35 pm

Hello Colin,

it is easier to fit the rubber to the glass then put the string, (although i prefer flexible electrical cable, nice and smooth) around the rubber. Trying to keep the string in an internal groove must be a night mare?

Alec

Post by **246gts** » Wed Dec 21, 2005 9:24 pm

Colin / Alec
When I took the screen out I actually released the rubber from the bodywork with a series of flat screwdrivers and pushed the glass and rubber into the inside of the car.
I always imagined the replacement to be the reverse of the above.
Dave

Post by **ColinP** » Thu Dec 22, 2005 8:45 am

Right, That's the difference!

Reassamble is simply the reverse of dissembly

And yes it was difficult!

Colin