Gutting car, defogging Q
#1
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Gutting car, defogging Q
As I'm in the middle of gutting my car I'm ready to ditch the HVAC system too. As the car needs some streetability I want to be able to defog the windscreen if necessary. I canīt find heated windscreens for the miata so I thought about using a bilge blower inline with a hose leading from the air intake on the RHD in the cowl area to the piping already in the dash.
Would one of these move enough air to be able to defog the windscreen?
Specs:
Output-open flow @ 12 volts - 135 CFM. Amp draw @ 12 volts DC - 2.7. Fuse size - 4 amps. Dimensions (including mounting feet) - 5-1/32" L x 5-1/16" W x 3-5/8" H
Something like this:
Mounted like this:
Would one of these move enough air to be able to defog the windscreen?
Specs:
Output-open flow @ 12 volts - 135 CFM. Amp draw @ 12 volts DC - 2.7. Fuse size - 4 amps. Dimensions (including mounting feet) - 5-1/32" L x 5-1/16" W x 3-5/8" H
Something like this:
Mounted like this:
#2
Cpt. Slow
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Why not hook the stock blower up to the defroster vents. Free minus some time, 4 speeds, already wired, already mounted, etc, etc. That's what I did but I also kept the heater. Want some scary under dash pictures?
Go to Keith's Targa build and click on the weight loss tag, the first few pictures are pretty informative, can't seem to find good pictures on the blower installation.
Go to Keith's Targa build and click on the weight loss tag, the first few pictures are pretty informative, can't seem to find good pictures on the blower installation.
#3
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Ditching that purely for weight savings. All the tubing will be removed, except for the defroster ones. The blower with some hose seemed simple enough to do.
Scary pics? Post 'm up
Scary pics? Post 'm up
#4
Get a rear defroster from E30 convertibles. Its a blower with a built in heating element (all electric) and is very low profile. I'm finishing a racecar build for someone and the guy is using one of those as his front defroster since he doesn't have a heater core. Its on a 68' BMW 2002 FWIW.
#5
http://cgi.ebay.com/ebaymotors/ws/eB...d=370356078800
It's not exactly cheap, but looks like it would work well. Maybe fab something up or drive with a roll of paper towel or regular towel in case the window fogs lol. I have yet to see how bad it will be in my car as I've ripped the entire HVAC out as well...
It's not exactly cheap, but looks like it would work well. Maybe fab something up or drive with a roll of paper towel or regular towel in case the window fogs lol. I have yet to see how bad it will be in my car as I've ripped the entire HVAC out as well...
#7
http://cgi.ebay.com/ebaymotors/ws/eB...d=370356078800
It's not exactly cheap, but looks like it would work well. Maybe fab something up or drive with a roll of paper towel or regular towel in case the window fogs lol. I have yet to see how bad it will be in my car as I've ripped the entire HVAC out as well...
It's not exactly cheap, but looks like it would work well. Maybe fab something up or drive with a roll of paper towel or regular towel in case the window fogs lol. I have yet to see how bad it will be in my car as I've ripped the entire HVAC out as well...
#14
ZX:
I ran without a heater core for a while, and rainstorms were a beyatch. You need more than airflow. For the same reason your car runs the A/C system when you use defrost, that the air needs to be dryer. If you heat the air you lower the specific humidity. It's basically the reverse effect of dew point in weather terms, which is oddly how an evaporator in a refrigeration cycle remove moisture from the air. One method is more effective, but the other is simpler, cheaper and lighter.
I forget all the scientific parts of it, but hotter air can take more water vapor before it's saturated. If, and I say IF the air you are blowing across the windshield is not saturated, or at close to 100% relative humidity, it will clear it up some.
In reality you find that point very quickly inside a Miata in rain and cold, unless you're fond of not breathing for long periods of time. Mine would fog up, front back to front. I could keep going forward once the side windows fogged, but once the windshield turned into "hazy flashback frame" mode I had to pull over, wipe, and repeat. The heater core hose routing rectified itself pretty quickly last fall.
You may very well know all of this, but due to your question I decided it would be good to relate this for posterity.
******:
How much does one of those BMW units weigh?
Last edited by gospeed81; 04-15-2010 at 07:53 AM. Reason: Not every day I get to teach a NASA engineer something
#16
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I was experimenting yesterday and today with my defroster (in my truck driving to work) to see the effect of just airflow versus heated air. It has been raining a lot here for days and so conditions are right for mild windshield fogging. Just airflow alone will clear up a fogged windshield a bit, but heated air is much more effective.
Most car systems work like you said. They are basically dehumidifiers. The air is cooled with the a/c, water condenses out, then it is reheated with the heater core, producing air that is much drier than when it originally entered the A/C system.
But anyway that is why I asked the question about the practical racing use of blowing air through the defroster vents with no heat source. All of this was in my mind, so I was skeptical that just using unheated air could work. But if it works, it works.
One could use the old-school method of pulling heated air in from the engine bay, or from a 'stove' around the exhaust pipe, but then there are safety issues with that too. I'll bet one of those bilge fans with a simple little low wattage DC electric heating element in the airflow would help quite a bit. Maybe a high current resistor with a big heat sink on it. Wire it to produce say 240W (20A@12VDC) of heat or so. Cheap, simple, light, compact. All I know is if I am out on the track, and my window fogs, I want to flip a switch and have that window clear RIGHT NOW.
#17
$30 buck heater/defroster from walmart. I remember this being 20 bux in the store for some reason. Plugs into the cig outlet.
http://www.walmart.com/ip/Koolatron-...eater/11710385
http://www.walmart.com/ip/Koolatron-...eater/11710385
#18
^^^ That's what I want...a completely electric solution that isn't off a german car and costs $100 used on eBay.
I'm about to get a manifold that will require me to reroute the heater return anyhow, so if I do away with the heater core altogether it will simplify things.
But yeah, just air, in a Miata, in any decent rain doesn't work well. I consider this steady state conditions since I was at cruise for 75 miles.
I'm about to get a manifold that will require me to reroute the heater return anyhow, so if I do away with the heater core altogether it will simplify things.
But yeah, just air, in a Miata, in any decent rain doesn't work well. I consider this steady state conditions since I was at cruise for 75 miles.