Re: rear-window defroster-connection

[Phil and Judy Rose <pjrose@servtech.com>]

Richard,
Devising a mechanical contact is a very intriguing suggestion. This heater
circuit is protected by a 30A fuse, so I suppose some significant wattage
and needs a decent contact. But hey, this is an Audi, it might just
work--maybe for quite a while!

Various ways to approach your idea: A strip of brass (?) could be tapped
for a small flat-ended screw: one (or both) ends of the strip could be
glued down and the screw adjusted to assure contact to the window patch. Or
it could even be simpler... Anyway, if it failed, it still ought to leave
open the option of soldering, or other approaches.

BTW, many have rightly corrected my assumption that a silver solder would
be a good choice if "low" temp were desired. A better surmise on my part
would have been "not-very-high-temp" plus better strength (than 60/40).
Anyway, I was misled on the heat aspect by some "silver solder" I had
around my shop, which advertised itself as having the benefit of "low
temperature" and being more suitable than the common Sn/Pb alloys "for
hobbyists" (whatever _that means_). But I can't find any data on
Ag-containing solders which backs that up--the Ag/Sn (4/96) melts about 40
deg C *higher* than 60/40 Sn/Pb, but is said to be stronger. On the other
hand, it would probably be lower-melting than 40/60 and about equal to
50/50 Sn/Pb.

I could move back to Arizona, where I was able get along without a stinkin'
defogger (of course that was so long ago that they hadn't been invented
yet).

Phil



>Just a thought, but rather than try to solder to glass (so to speak), would
>it be possible to glue (using mirror cement) a pressure contact that
>presses against those existing patches?
>
>BTW, I would expect silver solder to require more heat.  Good luck.
>
>Richard
>
>At 10:18 PM 8/1/98 -0400, Phil and Judy Rose wrote:
>>Ron,
>>Did you actually get this epoxy to work for a window defroster contact?
>>I have wondered if there was a nice 'n easy conductive epoxy suited for
>>this. If Ford made it, them maybe their dealers use it. I'll check.
>>
>>As to the ability to get the glass hot enough...well, dunno. There are two
>>small metal contact patches that are somehow bonded to the glass. I need to
>>make my solder joint to these small patches of metal. Doing it successfully
>>will require getting heat into them faster than the glass can conduct it
>>away (and without destroying the bonding agent that holds these contacts to
>>the glass). And without gravity helping the loose spade lug thingy to run
>>away.
>>
>>You don't recall the name of that epoxy stuff do you? :)
>>
>>Thanks,
>>Phil
>>
>>
>>>Phil...
>>> I have has success using an epoxie compound thaty had a copper substance
>>>in it for continuity.
>>>In fact as I recall Ford Motor made (or marketed) the product for precisly
>>>this application. I doubt you
>>>Will ever get the glass hot enough to melt the solder. Too much of a heat
>>>sink. I haven't looked for the product recently but it may also be
>>>available from the mass marketers.
>>> Good Luck
>>>  Ron Husak
>>>
>>>Message text written by INTERNET:quattro@coimbra.ans.net
>>>>Date: Sat, 1 Aug 1998 13:46:36 -0400
>>>From: Phil Rose <pjrose@servtech.com>
>>>Subject: rear-window defroster-connection
>>>
>>>Well, while waiting for some qlist BTDTs regarding resoldering a detached
>>>electrical connector to the edge of the rear window (gulp, it happened to
>>>the connector for the ground wire--on the right edge), I asked around
>>>locally. One auto glass repair guy said he doesn't try to do it "any more"
>>>because sometimes the window cracks (just replace the glass, he glibly
>>>advised). An Audi repair shop claimed to have some limited success doing
>>>the resoldering, but that their failures were not because the glass cracked
>>>(just bad solder-joints, I guess).
>>>
>>>So I'm inclined to give it a try myself in the near future (oh yeh, I'd
>>>best  get my ohmmeter out first and verify that there is good continuity
>>>>from the power connctor all the way to the ground connection point.)
>>>
>>>I have a 120W soldering gun and a 45W iron. Will probably use silver
>>>solder, which I assume will require low(est) heat. I think the 45 watt iron
>>>would be adequate (and safer), considering that the metal spade-connector
>>>is quite small and the glass is not a great heat conductor. Any words of
>>>warning or encouragement?
>>>
>>>Phil
>>>
>>>Phil Rose               Rochester, NY
>>>'89 100
>>>'91 200q                pjrose@servtech.com
>>>
>>>------------------------------
>>><
>>
>>
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>>         *  Phil & Judy Rose     E-mail:              *
>>         *                       pjrose@servtech.com  *
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>>
>>


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