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Old 08-26-2011, 11:57 AM   #1 (permalink)
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Solid State window defrost and dehumidification.

One issue in electric cars is keeping the windows defrosted/defogged, in a gasoline car you just crank the heat up, maybe flip the A/C on and cool the fog and frost off the windows and at least in my electric car the heat is the waste heat from the electric motor so the fan blowing air over the windshield doesn't do a whole lot.
In the winter we have the same problem in the house, if it gets cold enough outside and humid enough inside the windows in the house fog up and frost over, solution? turn on the dehumidifier, so why not put a dehumidifier in my car? there is space in the cargo area and if I could find a small enough one there is even space under the dash.
In my search I found that there are a handful of solid state, peltier junction dehumidifiers, so I picked up one that is good for 1,100 cubic feet of space, it draws 22 watts and the fan is the only part that makes noise, granted it's not as efficient as one that has a compressor it's much cheaper, smaller and at the times that moisture is an issue in a car are also the times that a little extra heat is welcome.
It showed up yesterday in the mail so the first thing I did after making sure that it works was to take it apart and see what is in side, it's not much more then two heat sinks, a peltier junction, a fan and a few micro switches to turn it off when it's full of water, if I had it hooked up to a drain and made a new case I think it could shrink down to a 4" cube.
Anyway, after putting it back together I stuck it in my car over night, about 10 hours in the car and it pulled about a cup of water out of the air, it wasn't extremely damp when I put it in there but it's really dry in there now and I can't wait to see how it works as the weather gets cooler and moisture becomes more of an issue.

How I have it hooked up right now in my electric car is I have a plug inside the car that hooked in to the charging plug, so any time the car is plugged in I can power a device inside the car, the only draw back to this dehumidifier is that it's always on, there is no built in humidistat, so that is the next addition, then I'll most likely just install it under the dash.
The other nice thing about it is, it takes 9v DC at 2.5 amps so altho the amperage is a bit high I could power it off a 12v battery, not sure how it would do if I just ran it right off 12v.

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Old 08-26-2011, 12:03 PM   #2 (permalink)
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Cool idea. I hope it works well for you.

Though, I must say I have a hard time believing that anything that only uses 22W of power can dehumidify 1,100 cu/ft.
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Old 08-26-2011, 12:21 PM   #3 (permalink)
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Quote:
Originally Posted by Daox View Post
Though, I must say I have a hard time believing that anything that only uses 22W of power can dehumidify 1,100 cu/ft.
Most of the poor reviews that I saw for them where people saying that it doesn't keep their basement dry or that it doesn't keep their 30 foot RV dry, but the people who got it for under the sink, or in a closet or like me, who got it for in use inside of a car, all seemed to be happy with it.
I would guess that the inside of my Civic VX is less then 300 cubic feet and my electric car is maybe 150 cubic feet, so if it was wired in with the block heater on a gasoline car then it would pull the moisture out of the seats, carpet and air for the few hours before you drove off, of course if it was that cold it might have issues with frosting up.
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Old 09-04-2011, 08:16 PM   #4 (permalink)
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The dehumidifier has been working as designed and advertised, pulling about a cup of water out of the air of the inside of my car while sitting over night.
I also have a 48v to 9v converter on order so that I can run it off of the main traction pack instead of off of the battery that runs the lights.
I also have some more heat sinks and fans on order and about to order some more peltier junctions so I can build my own, granted it only pulls half a liter of water per kwh out of the air, where an energy star rated dehumidifier is 1.2 to 1.6 L per KWH, but this is tiny! smaller then a toaster on end and the only moving part is the fan, weighs only a few pounds and runs off low voltage DC.
The other peltier junctions I'm getting I'm going to set up to work both for heating and cooling, because for heating 100 watts of energy input and I can get 150 to 200 watts of heat output because they are a heat pump and are reversible just by changing the polarity/flip of a switch.

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