Exothermic Windshield Defroster? Suggestions for a device to de-ice?

Thinking about how to make a device that will automatically defrost my car windscreen about half an hour or so before I get in the car.
I'm pretty sure the huge power consumption of heating elements disqualifies them from this project since it'll be battery powered and I don't much want to fill my car with batteries!

The second idea was to use a homemade burning laser, but I think that was just my evil scientist side popping up and was easily pushed down with arguments such as "it'll be way to complicated" and "it might blind someone".

My next idea was to use some kind of exothermic reaction and pass the heat on to the windshield either by direct contact or through some convection heat sink/fan combo. 

My questions:

1) Does this sound remotely feasible? If not, any better ideas?
2) What reactants would be suitable? The reaction has to produce enough heat over a long enough period to warm up and defrost at least a decent chunk of the windscreen without cracking the glass in the process (I know military MRE's produce heat enough to cook with for about 12 mins). Also the fewer messy reaction products the better (no filling my car up with poisonous gasses please!)
3) Has this been attempted anywhere else? Do you have details or a link? (couldn't find anything after a quick google search)
4) Why didn't my question appear after I tried to post it the first time? Does it have to be moderated first and am I going to look a bit  silly when the question appears twice tomorrow?


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oh ok is micron filtered work place just to prevent any particles being in the bags? i would have thought some people sell them though. thanks
iceng i don't think you understand my point. A hand warmer pad is a plastic sack of sodium acetate trihydrate, when you click a metal band in it, it causes an exothermic reaction that freezes the pack - hot ice, giving heat off. So my idea was to use a very large one to put on the windscreen. These go on the outside of the windscreen so don't get why you think that would effect the oxygen level in the car and the driver?

Why do you say a hand warmer uses oxygen to burn a fuel for warmth? are you talking about the ones that use metal?

I am not sure if you are being funny. I am doing a science fair project and wanted to get some serious answers here. Thanks. H.E
Exothermic crystal formation one time heat release .... I used to sell and demo them.
  • Each time they must be recharged.
  • They provide very good heat
  • if the get cold enough they self activate.
  • You need a micron filtered workplace to make a bigger one
  • Must avoid dust particle nucleation debris.
  • Even then some bags turn to sea weed and fail. 
  • The home Co did make a big ones that could wrap around you.
Yes it may work :-)

I have googled everywhere about windshield defrosters and no one is using extra large pads of sodium acetate trihydrate - why? makes sense to me, i am about to do my temperature experiments and that may help me. But surely the heat at about 60C isn't going to crack the windshield?
Please only helpful comments, I am 15 and don't get adult humour.
why can't you just use a bigger version of a hand warmer that is what i am making but maybe you know problems with it that i haven't thought of from H.E
A hand warmer uses oxygen to burn a fuel for warmth.

A bigger version will use more O2 and may lower the oxygen level in the car,
which can cause a driving error and all that entails !
Warm your car up by turning it on and blasting everything on full heat (also turn on the rear heaters) and when you come out the junk should be melted enough to shove off with a brush/chipper and the windshield wipers. I also think iceng's first idea is really good, I'll have to try it.
I'm going to ask  Steve how warm your winters are ;-)
How would he know? He's a brit and I'm from Michigan.

Our winters are usually 10-20F and when we get any substantial amount of snow, it really dumps on us. We also tend to get icy rain which is a real pain.

I wonder if I can find a black tarp at home depot.
Ideanator, I'm from the mitten state too, and you know you'll lose that tarp under a foot of ice and snow, and never get it off. And if the ice gods are really feisty, they'll have figured out how to nudge that tarp between the door and the car body, and freeze it shut. You won't get into the car until spring.
In retrospect, we've had quite a snowless winter so far, so a tarp would have just been silly.
Thats what heat guns are for, hehehe. But in all seriousness I'd expect the water to get under the tarp and freeze it to the windshield and THAT would be so much worse than a frozen door.
Where did I get the idea you were working for Steve.
He was interning for me for a few months until August
Ohh thank you.......  Always worried about senility here.
I do try to remember interrelationships on site.
Yes, what he said.

First hint of winter today, a bit of icy rain.
iceng6 years ago
  1. A simple outside wind shield cover with built in magnets to hold it in place can keep it frost free for you.
  2. Another way is an electric dip stick oil heater at night for non-ice starts.
  3. Thirdly an add on water heater that plugs in to AC line at night can make a warm car start all winter.
  4. In desperation I would pour a hot pitcher over the wind shield.  Be very careful you can crack your wind shield glass.
knife141 iceng6 years ago
+1, except for the pitcher of hot water.
iceng knife1416 years ago
Hey... I was a crazy nut,  never  cracked  ;-)
Re-design6 years ago
Nothing battery powered is going to generate enough heat without being very large. Think of adding a second car battery just to run the heating element.

Most chemicals that can produce that kind of heat would also destroy paint or interior if spilled.

Consider keeping the glass clean and apply rain-x.  It helps release any ice from the glass and covering the car when parked with a tarp that you can pull off thus removing any accumulate ice at the same time.

You could run an extension cord to a space heater installed in the car and let that clear your windshield for  you.
My Ford has a heated windshield that will melt off ice in about 2 minutes - power consumption is only around 100W.
adamnewt (author)  steveastrouk6 years ago
would it be possible to rig it to a timer so it starts melting ice while i'm still tucked up in bed?
Yes, pretty straightforward really. I'd suggest you did it shortly before you went to the car though.

And having seen the piddling batteries that are fitted to US cars these days, a backup plan might be a good idea !

How about using a jump-pack wireed to the heaters ?


Start with Iceng's window/shield/screen covers. These will let frost (most of it) form on top, not on the glass. Make or buy them. Whatever you do, DO NOT use hot water, or any water, on your frozen glass. Hot WILL CRACK the glass, cold will form more ice (if it is cold enough), making your job that much more difficult. 

For remote clearing of your vehicular transparencies, most people use one of these to do the job. The plus side is it is self contained, using existing systems to do the job, and you come out to a warm vehicle with clean,clear windows. Sometimes you have to trust the aftermarket.


Those are illegal in some countries, like the UK.
I understand remote starting poses a risk to populace
( politicians fear everything )
What does the UK think about total Electric vehicles ( Lethal all the time ) ??
No problem, and no tax on EVs. Remote starting is quite hard to interlock properly in aftermarket systems reliably...There have been some incidents.