A better way to defrost rear car windows?

[truereplica]

My dad has driven station wagons all his life.
He would rather quit driving than switch to an
SUV or some other big car.<p>He presently has a 1991 Taurus and Sable wagon.
Since the Taurus and Sable are almost identical
the parts purchased for one can usually be used
for the other.<p>The rear window defroster grids on both cars are
a mess. I tried repairing some of the grid lines
with some conductive silver based ink. After
repairing a couple of line I realized that I
would have buy two or three hundred dollars of
the stuff to repair all the damage to both grids.
Even when the grids worked, they did a lousy job
defrosting the rear windows.<p>I have an idea (which my dad immediately liked) to
install some kind of hot air blower in the rear
of both cars. The problem is these cars have
liftgates. A standard two or four door sedan has
a rear shelf that you could cut a hole in to
install a blower.<p>I've seen air distribution systems that channel
air through a plastic tube. Holes are drilled
into the tube for nozzles or jets that distribute
the air evenly. This sounds like a simple enough
idea but actually obtaining a blower that could
force enough warm air through a 1/2 or 3/4 inch
tube is difficult, to say the least! Finally,
you have to deal with that 12 volt battery. A
200 watt blower would consume over 16 amps of
current.<p>My dad thought about replacing both rear windows
but that would leave him with defroster grids that
he never liked much in the first place.<p>Any suggestions would be appreciated.

[Chris Smith]

Even a half ass defroster grid with fresh air is better than a bad heater grid alone. <p>Warming up the window only makes DEW and high humidity, while the fresh air dehydrates some of the water out of the air and window surface to clear the window up some what faster. <p>A simple small box about 2 inches square on the up stream air intake [you have to plumb it] with a small fan in side and a peltier or two would be small and easy to install, while consuming less than 10 amps over all, and would aid in the warming and dehydration cycle. <p>Stacked peltiers get quite hot, while the cold side will condense some of the water away from the inside of the car. <p>The hose and plumbing are really the hard part.

[Newz2000]

Here are some ideas:
Blower
Peltier Thermoelectric heater/coolers
Heatsinks (to attach to the peltier's)<p>One side of the peltier gets hot (relatively speaking), the other side gets cold. Attach the heatsink to the hot side (dictated by polarity) and then use the blower to pull air across the warm peltier and then onto the window (through a duct probably).<p>*they say* (haven't confirmed) you can get a 30 - 50 degree change in temp between the hot and cold side of the peltier. If it's 0 degrees in the car the peltier might drop to -25 on one side and +25 on the other, which won't help too much. I've never tried stacking them like Chris suggested, but if you could get a higher delta then it should work.<p>You can use PWM to control the effect of the peltier, so you can have an adjustment knob in order to make it warmer. You can also control the blower using PWM so that you don't go deaf from the sound.<p>I'll bet you could get the above working with a single peltier so that it used under 5 amps. Peltier's are heat pumps, not heaters, so they just move the heat around. <p>**disclaimer: I've lived in FL for the last 8 years and am just about to learn what winter means in the north (honestly it's only the beginning of october and it's already been down in the 40's!). My investigation/experimentation with these TEs is to make things cold, not hot.

[jollyrgr]

I've lived near Chicago all my life and trust me; I know what a cold winter is. (Its been colder in Chicago than in Alaska in winter.) I know what it is like to have a malfunctioning defroster grid. When it gets REAL COLD even the grid takes a while to work.<p>That is why I have one of these:<p>http://www.harborfreight.com/cpi/ctaf/D ... mber=36711<p>I don't have the same brand but I have the same type of device. These things are not super blow torches but will clear a window in freezing cold weather before the engine heats up. I've simply set these on the back deck of sedans and then plugged them into the cigarette lighter and they work okay/better than nothing. On SUVs you could mount this above the door on the ceiling or below the window on the doors. Same for the station wagon. In your case you could mount this on the door with "Velcro" tape strips or magnets. Connect the power to the defroster grid to this blower (then your dad won't forget to unplug it and cause a dead battery). The combination of the working grid lines and the blower (or blowers???) will do some good. These also work immediately and can help clear a windshield. Using Velcro and some sort of Molex connector (or even a cigarette lighter female plug on the door) will allow you to remove the heater when the lift gate needs to be folded down. Using the power to the grid lines will allow the wiring to move with the door and thus stay connected to the blower. Removing the blower when using the tail/lift gate is a simple matter of unplugging a connector and pulling on velcro or magnets or whatever temporary mounting device you decide on.<p>In high school I used a small electric space heater in my "Country Squire" station wagon to warm it up and clear the snow. My alarm would go off, I'd open the back door and plug in the extension cord leading to my car and the space heater sitting on the front seat. There could be six or more inches of snow on the car when I plugged it in. By the time I finished getting ready for school, the snow would be melted off all of the car except the hood.<p>
Not to be mean but this is a good place to relate this story.<p>We had an "open house" for a young kid (13 YO) that stayed with my family for a week when I was young. This kid was from southern California and had NEVER seen real snow in person. I had this huge Cadillac (1974 Fleetwood). This thing was a tank, it had fold down foot rests in back, we are talking big. So big that I stored my winter scraper/snow brush under the driver seat. Anyway my brothers, this kid, and I were going to a movie. This is in the middle of July so my snow brush is under the seat. This kid is playing with the footrests as these were something he'd never seen in a car. This is when he noticed the snow brush/scraper under my seat. He pulls it out and starts examining the thing. In a surprised voice he said "WHAT IS THIS THING?" My brothers and I started laughing as we realized he'd never seen snow before so he'd never seen snow brushes before. We explained what it was. He thought it would be easy to just brush the snow off with our hands.<p>There are probably things that are used in Florida and southern California that I've never seen. Someday maybe I'll be surprised by some weird contraption like this poor kid was.<p>Down into the 40's? Where did you move? In my winters, we look forward when it will get UP into the 40's! <p> <p>[ October 11, 2005: Message edited by: Jolly Roger ]</p>

[Newz2000]

To be fair, I grew up in Iowa and didn't move to FL until I was 21, but you'd be amazed at how quick you adjust to the fair weather.<p>I've been to Chi in the winter and you're right, it is surprisingly cold there. Something to do with the lake, I'm sure.

[Dean Huster]

Back in the days when they were first starting to put the heating grids on the rear windows as an option, one of the car makers (I think it was GM, but not sure) had a version that was a warm air defroster.<p>If you want to really do it with a LOT of warm air but don't want to tax the electrical system, I don't see why you couldn't run a pair of smaller hoses in parallel to the heater hoses back to the rear deck to a little heater core. Heck, if school busses can put heat in the rear like that, surely you could defrost a window that way, too!<p>Dean

[truereplica]

Thank you very much Chris Smith, Matt Nuzum,
and Jolly Roger. Your responses to my post
are really fine!<p>Just to let all you guys know, I experimented
with every kind of electrical, electronic, and
electromechanical gizmo and gadget when I was
a teenager. I subscribed to all the electronic
hobby magazines. I remember seeing one of the
early classified ads for Nuts & Volts. I guess
I was one of the few who got a free lifetime
subscription. When Nuts & Volts became a full
color magazine printed on slick, high quality
paper I was waiting for the notice informing
me that my "lifetime" subscription could not
be sustained. Well, I never received that notice.<p>Using peltier thermoelectric modules is a really
interesting idea. I suppose you could come up
with something that would do the job without
overtaxing the battery. You're right about the
plumbing part of the job Chris. Just thinking
about it reminds me of that famous W.C. Fields
remark when he said something like, "whenever
I get the urge to exercise, I lay down until the
urge goes away."<p>My family and I have also experienced driving
through some dangerous ice and snow storms over
the years Jolly Roger. I don't remember when
defroster grids first started appearing on cars.
I never liked the idea or the design. They work
ok if your rear window is covered with heavy dew,
mist, or fog. Dump a thick coating of ice or
snow on the window and they just can't melt it
fast enough. The smearing and streaking that
occurs gives you a completely distorted view
through the rear window. It might be better to
rely on side view mirrors with long extensions
like you see when someone is towing a trailer.<p>I copy and pasted all your replies into a text
editor so I can stare at them when I'm offline.
I find that if I read something several times
I occasionally get off my butt and go into my
under utilized workshop.<p>I just noticed your reply to my post Dean Huster.
Thank you too Dean!<p>truereplica<p>[ October 11, 2005: Message edited by: truereplica ]</p>

[jollyrgr]

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by Dean Huster:
Back in the days when they were first starting to put the heating grids on the rear windows as an option, one of the car makers (I think it was GM, but not sure) had a version that was a warm air defroster.<p>If you want to really do it with a LOT of warm air but don't want to tax the electrical system, I don't see why you couldn't run a pair of smaller hoses in parallel to the heater hoses back to the rear deck to a little heater core. Heck, if school busses can put heat in the rear like that, surely you could defrost a window that way, too!<p>Dean<hr></blockquote><p>Come to think of it, I believe that my '74 Cadillac had a warm air defogger in back.<p>As far as running hoses and what not to the back window; this COULD work. In fact my Suburban has rear AC/heat and hoses run to the back for both the refrigerant and heated water. But the electric grids on the rear windows work faster than the engine heats up. While I don't like the grids; they are better than waiting for engine heat. <p>This winter it is not likely that I'll be having my car in the garage. I may have to put a space heater in it....this time on an automated system.<p>[ October 12, 2005: Message edited by: Jolly Roger ]</p>

[Chris Smith]

There is another alternative. <p>Up here when my windows would freze over in winter, [minus 20 plus] I would place a heat lamp in the car for the defrost to begin before driving my car. <p>A 12 volts solution of IR heating lamps could work, and they are much faster on the warm up cycle. And not much trouble on the installation either.

[Joseph]

Being the rear vertical window makes the following idea less useful for the problem at hand, but I thought it might be interesting, nonetheless.<p>I had an '80 Chevy Citation. Realizing that since it had AC, it probably had a 55 ampere alternator, I decided to put a high-power heater on the dash under the windshield to warm the inside and to defrost the window while the engine was warming up. It was just some 24 gauge wire wrapped around nails on a 1/4 plywood support shaped so that it did not block the defroster vents. Stop thinking "fire hazard!" It was relative luxury compared to waiting 5 minutes for the engine heat to kick in.<p>Sure, it bogged down the alternator and subsequently the engine, but I almost always turned it off before driving away. The snow and ice would practically just slide off the windshield within about 30 seconds. Plus, it raised the inside temperature by about 20 degrees within 2 minutes. It drew close to 500 watts, I'd say.<p>[ October 12, 2005: Message edited by: Joseph ]</p>

[Dean Huster]

Joseph, how could your heater be any worse in power consumption or any less practical than these massive current-consuming power amps that the kids install in their cars?<p>It seems to me that I've heard of instances of car windows cracking in super-duper cold weather when the defroster strips kicked in. Of course, my old F-250 did that with the windshield with the regular defroster, too ... back when it actually blew warm air into the cab.<p>As long as the car was running, I'd think that Joseph's idea (especially if placed in a metal box that was safely mounted somewhere with a small blower motor added to drive the air out both forward and backward to help out the two main windows) would be wonderful.<p>Chris' heat lamp idea isn't bad, but I'd think that a regular space heater (again, properly positioned) might be a bit safer. Or maybe not. Still, any 120vac solution isn't going to work after the car's collected an inch of ice while sitting out in a parking lot at the factory.<p>Dean

[Chris Smith]

The hot water idea is the best bar none, BTU for warmth, bar none even including the delay time for the water warm up,.... but,.... the plumbing of the hose from front to rear, mounting of the small heater core plus Fan, air ducts etc are a bitch. <p>Been there, done that one. <p>And the worse thing of all, is the leak factor. <p>If you place two valves in line to cut off the water flow, WHEN it leaks, you are not crippled WHEN the core leaks, and your car is still usable! <p> Also, from my personal experience, the core or hose will leak when its least convienent, and steam up the entire car. <p>And you thought a foggy rear window was bad in winter? <p>Having done the hose and core trick back in the 80s, it works when it works, and it screws you when you can least afford it? <p>But you cant beat the BTUs or heat from a core.

[Bob Scott]

Doesn't anyone in the US use plastic frost shields stuck to the inside of the car windows? Or are they only sold in the colder parts of Canada? They are passive devices.<p>Bob

[jwax]

Plastic frost shields? What is that, Bob?

[Joseph]

Dean, some more thoughts came back to me today concerning that heater. I remember now, I didn't even run the car when the device was on. I figured at the time that it would actually preheat the battery for when it became time to hit the starter. Now for the environmentally bad part. The car ran too poorly when cold for me to start it and then take my foot off the accelerator. <p>Simple convection was all the device used, and the lack of a blowing fan even concentrated the heat. I had actually been expecting the windshield to crack, but it never did even after a few winters of use. Also, the plywood strips of wood became quite charred over time, but they never flamed up.