Heated Mirrors

Turn on the rear window defroster and the heated mirrors come on. We wouldn't want to drive around town with cold mirrors.

 

rear window???? i thought the heated mirrors run off the front window defroster

 

I think so too.

 

rear window defrost activates the mirrors too. In winter when I pull into a car wash, the rear views instantly fog up. Hit the rear defrost, they start to clear. I finally got into the habit of hitting the rear defrost button 30 secs before entering the car wash, problem solved

Note: this was at temps of -25 C and colder

 

It's getting close to winter and my co-worker just added heated mirrors to his Mazda 3. So.... In true IT guy / Gear-head fashion, does anyone know if I can get the stuff aftermarket to add heated mirrors to my '05?

Wouldn't want to be shown up by either a Mazda or a Co-worker

 

Anyone think that these would be decent?

eBay Motors: 04 05 06 07 Toyota Prius Side Power Heated Mirrors Pair (item 310088147057 end time Oct-29-08 14:23:10 PDT)

Not to be annoying but new projects excite me.
Will the '05 be wired for the power mirrors already? Not a problem if not. Just curious. Also, my car is white so I don't know if the black would look good. Any thoughts? Anyone think that the white covers from my factory mirrors would fit these?

 

My last vehicle got upgraded to heated mirrors somewhere around its 16th birthday, which happened to be when the silicone blobs that bonded the mirror glass to its mounting started to let go and the glass got loose - I noticed when the image of the road behind me shifted upwards every time I stopped and downwards whenever I accelerated.

So I pulled the glass the rest of the way out, scraped off the old silicone, and bought a couple 10 ohm, 10 watt power resistors at Radio Shack. Crunched up the resistors with a small hammer until I could unwind the wire inside; each resistor gave enough wire to make a nice W on the back of one mirror glass. Tacked the W down temporarily in a few places and then smeared a W of silicone caulk over it; let it cure. Used a little more of the same silicone to secure the glass back to the mount; wired a switched 12V circuit to the ends of the W. Makes for about a 15 watt mirror heater (each side), which seems to be about right in an Indiana winter.

Already had the silicone; I think the pair of resistors was $1.99.

And yes, I am thinking of doing the same thing to the Pri. As soon as I figure out how to pop these mirrors out. I've read about it on PC, but the last time I looked at the mirror it wasn't obvious where the tabs were or how to release them.

-Chap

ps. It's the silicone caulk as much as anything that makes it work - has silicone's resistance to softening under heat, and conducts the heat rapidly and evenly to the glass so nothing gets more than warm. My first attempt had been to just tape the wire to the glass - wire just melted through the tape in seconds on the first test.

 

Hi Brian,

I believe your car is already equipped with heated side mirrors.
2005 Toyota Prius standard equipment at Edmunds

 

I added heated mirrors to my old SHO. I bought a set of Lincoln Continental heated mirrors and took the heaters out and installed them in the Taurus mirrors. It worked like a charm.

 

You officially have the most useful post that I have received yet. I went out and looked with a thermal gun. Sure enough, they are heated. I must not have left the defrost run long enough last winter to notice. I was always scraping ice off of them.

The heat topped off at 86 F. Sound right?

 

Too bad the answer "you already have heated mirrors" doesn't work for me - I have a Generation 1. But I did at last figure out how to pop the mirror out. Pretty much as described in other posts, but I spent a long time hunting for the tabs, so I've attached a scan (100 dpi) that shows them. It's nice that the more outboard tab has a little hole directly beneath it in the rim of the glass mount. With the mirror aimed as far up as it'll go, a thin screwdriver can just feel where this hole is. Then it's just straight up to find the tab.

The tab isn't something that has to be pushed back to release - all that's necessary is to get a thin screwdriver blade between the glass mount and the mechanism it clips to, then twist the blade gently and the tab pops out. After doing that for the one with the locating hole, it's easier to find the other one.

Then the bottom edge just lifts up and out until the hinge-like tabs at the top release from the mechanism - but the mechanism (which was aimed fully up to access the lower tabs) now has to be aimed down before the glass can tilt up far enough to clear.

I did find a catalog online that will sell bare glass for a G1 Prius: #215 for the driver's side, #1843 for the passenger. Can also order a silicone adhesive specialized for mirrors; apparently, the more common silicone products may chemically degrade the reflective coating.

I never ran into that problem with the retrofit on my old Ford because its side mirrors were coated on the first surface (check: a pencil point touches its reflection) so the silicone on the back only touched glass. Here it could be a concern because Toyota coated the second surface. At least that makes the mirrors less vulnerable to ice-scraper damage - on the Ford I really, really wanted to add heat so I wouldn't have to scrape the first-surface mirrors.

The web site shown above will also sell a purpose-built cut-to-fit heating element to simply stick on the back of the glass. It's $25, though, or about 25 times the cost of a power resistor at Radio Shack.

Getting into the project, though, would require separating the glass from this plastic glass mount (that's a square of foam double-stick showing through the center) without damaging the second-surface coating. And maybe, since the second-surface mirror is scraper-safe anyway, maybe I don't need another project just now. At least now that I know how to do it, it will be easy to pop out again if I change my mind.

-Chap

 

Whether you want to new project or not. Your solution is genius. I don't think that I would have ever thought of that but both my boss and I agreed that it would work well. I'm thinking of adding a switch and doing it on my Intrepid.

 

I'm glad you like it! I think of it as "making what you want out of what you can get" which I saw once in somebody's .sig as a definition of 'engineering'. Coming up with it was basically a matter of:

- looking up the amperage and figuring the wattage of the rear-window defog

- measuring the area of the rear window compared to the area of the side mirror, and figuring the proportionally reduced watts

- guessing that a wire-wound power resistor would have enough wire to do the job, and seeing how close I could get to the calculated wattage with something in stock at the retail store

- discovering that tape wouldn't work, but silicone would.

As I think about it, I'm realizing there could be more concerns with doing this on a second-surface mirror:

- even if the special silicone doesn't react and discolor the mirror coating, the metal resistance wire might.

- hmm, I wonder if the mirror coating might be ... conductive? and short the element?

So it'll probably require great care to bed the wire W in a silicone W so that the wire isn't touching the mirror directly anywhere - maybe put down one layer of silicone first and let it get semi-hard?

And that might change the thermal transfer to the glass compared to direct contact, maybe or maybe not enough to be a problem.

-Chap

 

Hi All,

The way the rear view mirror defrosters work is with a PTC (Positive Temperature Coefficient) film resistive element. I have had aquantance of the inventor of this film (made by Illinois Tool Works - ITW). As the ink gets hotter its resistance gets higher, and less current flows. Thus the temperature is self regulating.

Resistor wire is designed to be ohmic - does not change resistance with temperature. So, its probably a bad idea to use it to defrost mirrors.

Maybe you can glue a bunch of these PTC thermistors to the back of the glass and run current through them?

 

It's only bad if it does something you don't want it to. The only thing it's been doing for me since I first tried it eight years ago is melting ice in the winter. Good enough for me.

I'm sure the PTC stuff is nice. But then the straight ohmic behavior is simple and predictable; you know E and R so you know the watts of heat you'll produce, which will be dissipated through your mirror. The disspation rate is proportional to the mirror's temperature, so it's already going to hit an equilibrium somewhere. The precise equilibrium temperature will depend on the ambient temp and wind, but if it doesn't get hot enough to damage anything in your kitchen before you put it back on the car, it won't under operating conditions either, and why would you care much about the precise temperature as long as it melts ice? There's a pretty wide range of behavior that counts as "ok".

I should go check the area of the truck side mirror though; it's bigger than the Prius mirror so maybe something < 15 W would be adequate on the Pri. But the 15 W on the truck mirror wasn't anywhere close to producing an uncomfortable temperature, so even if it would be oversized on a Prius I wouldn't expect it to be grossly so.

-Chap

 

Hi ChapmanF,

I think a few minutes looking through PTC Thermistor data sheets might be worthwhile and reduce the current once the mirror is hot, save electricty, and avoiding melted mirror brackets.

 

Hi donee,

Sorry I didn't see your post sooner. As someone who sometimes gets chided myself for overengineering things, I guess I really can't knock the taste of my own medicine. On the other hand, I hope I mentioned that I did this on a Bronco II and have since driven it through 8 winters - 8 years of troublefree operation goes a long way toward addressing speculative concerns.

I did find this PTC mirror heater patent description that I thought helped clear up what the excitement's about. Some of the techniques for making heated mirrors involve creating a planar resistor where current flows between the entire reflective mirror coating as one electrode and a 2-D conductive layer as the other, through a thin (and we hope uniform) layer of resistive stuff. Schematically that looks sort of like a(n infinite) mess of resistors in parallel, and you would really want them to have positive temperature coefficients because you don't want any regions of locally lower resistance to become runaway hot spots.

The same patent write-up also says that "the other" type of mirror heater design is a non-PTC resistive element that looks like a series connection. That's a fair description of what I did 8 years ago.

I never did get around to adding a timed off switch, which means there was that time I left it on for two days. I made three trips in the meantime and it took me all three puzzled moments ("why the slow cranking? did I leave something on?") to realize it. After two continuous days the mirror glass was definitely warm, even uncomfortably so, but nowhere near melting anything.

That was with ~ 15 watts of heat on the (larger-style) Bronco II mirror, achieved with a 10 ohm resistor. Scaling down to the area of a Prius mirror would suggest about 10 watts, so I would lean toward a 15 ohm resistor. Two 10 watt mirrors added to the Prius defog circuit and left on for the whole 18 minutes before automatic shutoff would be a whopping 6 watt hours consumed. Any amount we'd hope to save with a different heating technology could only be a fraction of that.

-Chap