The link TO6 put up says they use 10 times the amount of power I estimated, but they are heating the engine and all the anti-freeze. I was estimating enough to defrost the windshield. That gives me a good feeling about my opinion of the power required.

 

I think the only way to overcome the total power issue is to 1) limit the area that the heater thaws, and 2) control the heater so that the window is not heated anymore than it needs to be, and maybe 3) auto shutoff if a low battery is detected.

I'm picturing a sort of heating pad applied to the inside of the window, and insulated from the interior of the car so that all the heat goes into the glass. This would clear a window just large enough to get going safely. (One could argue that anything less than 100% clearing is not safe.) This strategy would require the user to apply the pad in advance, when they stop their car. I don't think that's a good solution. Laying a blanket of some sort over the outside of the windshield would probably be more effective and wouldn't use any power. But who wants to bother with that?

A nichrome wire worries me - without careful control it would apply too much heat in a concentrated spot and risk cracking the glass.

 

Laying a blanket of some sort over the outside of the windshield would probably be more effective and wouldn't use any power. But who wants to bother with that?

tons of people "bother" with that..

"windshield snow covers" are sold at just about any car parts store/online retailer,etc.. They require NO electricity...no worry of battery deep cycles killing your battery..

A battery operated solution is NOT a good idea one.. Nothing worse than a product that is just about guaranteed to shorten typical automotive battery life. Now if we all had deep cycle rated batteries then its not so much of an issue..

 

When I operate mobile radios I use a separate deep cycle marine battery for two reasons:

1. If I drain the battery I won't have to go home barefoot.
2. They are designed for steady discharge as opposed to several seconds of cold crakning power.

Your application is similar in that you want to apply power to a load for some period of time and then shut it off. You might want to try this approach at least in the development phase. Then you can see if it will be practical when run from the main automotive battery.

 

I think the only way to overcome the total power issue is to 1) limit the area that the heater thaws, and 2) control the heater so that the window is not heated anymore than it needs to be, and maybe 3) auto shutoff if a low battery is detected.

(One could argue that anything less than 100% clearing is not safe.) This strategy would require the user to apply the pad in advance, when they stop their car. I don't think that's a good solution. Laying a blanket of some sort over the outside of the windshield would probably be more effective and wouldn't use any power. But who wants to bother with that?

A nichrome wire worries me - without careful control it would apply too much heat in a concentrated spot and risk cracking the glass.

Thanks for replying,
great points made and you seem to grasp my concept and issues with the power are my main concern i thought i could possibly build a system to both as your points suggest firstly, only heat the glass when it needs heated according to the change of resistance . Secondly auto-cut off for the battery.

Thanks again for your reply

 

One point I noticed was that you intended to place your heating element

"around the periphery of the screen"

You are facing an uphill battle against the heat transfer coefficient of glass by doing that.

I know you Scots like uphill battles but....

 

One point I noticed was that you intended to place your heating element

"around the periphery of the screen"

You are facing an uphill battle against the heat transfer coefficient of glass by doing that.

I know you Scots like uphill battles but....

Thanks for your reply and yes we sure love uphill battles lol.

The heat transfer into glass is a huge obstacle but assuming that the ice melts where the wire is then would the then sheet of ice slide slowly to meet its end at bottom of the screen?

These interactions are really helping me look at my project from an outside perspective thanks again everyone

 

The heat transfer into glass is a huge obstacle but assuming that the ice melts where the wire is then would the then sheet of ice slide slowly to meet its end at bottom of the screen?

many factors at play there.. could be cold enough outside that all you do is generate enough heat to just warm the area a few mm outside of the heater band..

I'm fairly sure that Ford was including "front windshield" defrost strips in their vehicles not too long ago..

oh and http://www.youtube.com/watch?v=lLoTaEJGiWg
http://heat-clean.com/?product=lifepo4-battery-heatstick
http://heat-clean.com/?product=heated-wave-black

might want to look into already patented products if you do intend to develop/market this.. You could spend time/money developing a product..releasing it to market..then getting a nasty letter from lawyers demanding you to stop and all your work is wasted....

 

im thinking of using nichrome ribbon around the perimeter of the windscreen

That would defrost only the perimeter. Is that what you want?

 

Just melt the ice with some of that liquid that is found throughout your country - whisky.

Really, a bucket of warm water does wonders. If you can use the windshield wipers soon enough, the windshield will still be warm enough to prevent re-freezing. My son does this with his car every morning in Pittsburgh.

 

Fill your windshield wiper fluid reservoir with salt water, insulate it like a thermos and put a small PID or thermostat controlled immersion heater inside. Then hack the windshield wiper/sprayer system to start spraying & wiping at the the touch of a (bluetooth) button. This way you store energy (heat), and also employ chemical methods of deicing, both of which reduce the demand on the battery when deicing time comes around.

Or find a sleeker, less lossy way to store energy, and a less corrosive chemical means of deicing (glycerol maybe?).

 

The deicer is standard equipment up here.

Salt is pretty corrosive.

The heater/spray idea sound good.

Wipers may be froze down. We never turn them on without giving them a flop first.

10 inches of snow predicted here. It would be a tough job to handle that.

The basic defrost could be done with a fan and heat from the inside.

 

In case it isn't clear from what you are hearing, the electronics to control a nichrome wire heater are viewed here as pretty simple and trivial. The problem is, you could build a sweet nichrome wire controller but few here think that would solve your larger system design challenges.

If you want to run some experiments, forget building your own heater - just get some of those battery-powered socks.

Here's an out-of-the-box idea. Lay a big long bag of hot pad liquid on the dashboard, with a remote controlled trigger. These liquid hot pads contain a supercooled salt solution that release a buttload of heat when triggered. The salt crystallizes and can be recharged repeatedly with heating. I'm a little skeptical that enough of the heat could be transferred to the window, but I do think it would make a dent.

 

Hey guys, remember the point of school/college projects is as a learning exercise.
You can get at least as many marks by not succeeding in your original objective but producing a good investigation as to why and what would work as you can by simply trotting out a bog standard rote design.

 

Hey guys, remember the point of school/college projects is as a learning exercise.
You can get at least as many marks by not succeeding in your original objective but producing a good investigation as to why and what would work as you can by simply trotting out a bog standard rote design.

That's true. I once read of a unique project to make three legged underwear to extend use from one day to a week.

It was just done as an exercise in out of the box thinking.

 

You can't wear normal underwear for a week?

 

Fill your windshield wiper fluid reservoir with salt water, insulate it like a thermos and put a small PID or thermostat controlled immersion heater inside. Then hack the windshield wiper/sprayer system to start spraying & wiping at the the touch of a (bluetooth) button. This way you store energy (heat), and also employ chemical methods of deicing, both of which reduce the demand on the battery when deicing time comes around.

Or find a sleeker, less lossy way to store energy, and a less corrosive chemical means of deicing (glycerol maybe?).

Thanks for reply, and yes valid points the heated washer fluid has been done to a very high standard,
http://www.heatshotusa.com/wp-conte...Technical-Presentation-September-2011-USA.pdf

The use of chemicals put me of the idea.

This method is brilliant in my opinion and i stumbled on it half way through my project http://news.cnet.com/A-high-tech-way-to-defrost/2100-11395_3-6061333.html

thank you kindly for taking the time to reply

 

Here's an out-of-the-box idea. Lay a big long bag of hot pad liquid on the dashboard, with a remote controlled trigger. These liquid hot pads contain a supercooled salt solution that release a buttload of heat when triggered. The salt crystallizes and can be recharged repeatedly with heating. I'm a little skeptical that enough of the heat could be transferred to the window, but I do think it would make a dent.

This sounds really interesting if i could make it discreet enough it could prove to be a good solution to the problem.
Thanks again for replying i do really appreciate it

 

Just melt the ice with some of that liquid that is found throughout your country - whisky.

Really, a bucket of warm water does wonders. If you can use the windshield wipers soon enough, the windshield will still be warm enough to prevent re-freezing. My son does this with his car every morning in Pittsburgh.

Thanks for replying and i must admit i do use look warm water at present just find it a hassle and if living in a block of flats may be unpractical.

 

This method is brilliant in my opinion and i stumbled on it half way through my project http://news.cnet.com/A-high-tech-way-to-defrost/2100-11395_3-6061333.html

thank you kindly for taking the time to reply

I have 3 things to say:
1. Wow
2. WTF
3. Yeah, but you still need the car running.