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Re: [T3] '69 to '68 rear window defroster


On 2 Feb 2002, at 13:58, Dave Hall wrote:

> I was assuming 12V at the heater - do you get as much as 14.1V there when
> running with old wiring?  I've never bothered to measure it.   I just used
> V-squared x R, which gives 14 Watts for 12V and 10 ohms.  Good enough for a
> working value as most are much higher resistance than that now.  Never got
> near enough to a new one to know it was only 45 Watts, hence the admission
> of a guess on that. 

I really don't think the age has much to do with the voltage as long as the 
wiring harness hasn't been abused; there's lots of misinformation on this out 
there, sort of like the BS we see coming out of the audiophile folks 
sometimes. You know: Virgin copper vacuum refined under a full moon in a 
holistic pyramidal chamber. With the relay under the back seat, the voltage 
should be just about whatever the VR is regulating at.  

I thought I remembered 45 Watts from SERVICE Without Guesswork, but 
when went to confirm it, I found that once again my memory was wrong. It 
says 60-70 Watts, which for 14.1 Volts comes out to about 3 Ohms. So 
anything above 10 Ohms is probably pretty much dead.  

What I think I see on these windows is that there is a base layer which is 
brown and non-conductive. Over this is laid a resistive layer which was silver. 
I think the silver layer is fragile while the brown layer appears to be quite 
indestructible. What most of us have left is just the brown layer. I suspect 
that I actually cleaned off my resistive layer slowly by cleaning the inside of 
the window every year or so with Windex, even though I thought I was being   
careful.   

I have repaired small gaps (scratches) in the original silver layer, but 
someday I'd like to try masking and replacing a whole strip. I think the 
conductive paint is still available in very small expensive bottles.

-
*******************************
Jim Adney, jadney@vwtype3.org
Madison, Wisconsin, USA
*******************************

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