Building a heater into rear defroster blower hose

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glhx

glhx

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im thinking of a heating element that gets hot like a soldering iron and heats the air....i want it to look somewhat factory and be pretty small.

i would mount it inside a metal piece of pipe in between the blower and the rear defroster duct

now i need to find something that gets hot enough to make a difference and use dc power....about as much power as a grid defroster.....maybe a resistor would work...

2ohm 100watt resistor ...or 1ohm 200watt
running at 13.5volts ....dissipation would be 91watts+....amps would be 7+.....
wire to run it would be #14 or 12.
i think that could create enough heat to make the air warm....then with a variable switch i could raise and lower the voltage....a 75 watt bulb seems to make lots of heat and in a contained metal pipe it should be ok.

I dont like how big the resistor has to be at 200watts 1ohm
7"x3"

any input on something more compact or more economic will help......i live in a colder climate...i need a rear defroster...the blower doesnt cut it...i do use it
 
i like it.....gonna check into the rx 7 deal and that heater...it looks like that heater has a long resistor in there....similar to what im looking for....ive seen a lot of them but not that one

it needs to fit inside a metal version of this hose that connects the blower to the plastic duct...look at the 6x9 behind it....i have about ½ of that to work with
 

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i say ½ because i dont want the plastic duct to get too hot by being directly by the resistor....and want the factory look with good cfm power to get some force to the window......i might even upgrade the blower fan to something stronger...................im looking to upgrade m y heater blower and install side vents on the dash to hit the side windows
 
The factory setup (Imperial and other C-bodies) used a heater core and tapped into the heater hoses up front. The had their own heater box mounted under the package shelf to hold everything together. It wouldn't get instantly hot like an electric one but once you drove a ways it worked pretty good and didn't draw much current like an electric one would.
 
Some BMW convertibles have a very nice little rear defrost / hair dryer unit too. It's built by Seimens. It has a resistor and heatsink inside. they are hard to find and not cheap.
I'm sure other imports have or had similar units.
 
Something to consider... If a unit is designed for a very small glass, you might need 2, left and right to clear a huge rear glass in something like a B'cuda.
 
That sounds like something the factory should have done. It would also heat the interior faster. My heater box is in my Duster without the core hooked up I use the defrost on sometimes. This gives me an idea to incooperate an ellectric element in the box. Some of the ideas members come up with on this site are real creative. That is one thing I like about this site. I can't wait to see where this goes. Steve
 
http://www.sportsmansguide.com/net/cb/12v-swivel-heater-fan-defroster.aspx?a=580273

Heat, fan, maybe connect it to your duct? I am seriously considering this for my rear defrost in my duster.

http://www.jcwhitney.com/12-volt-ha...lding-handle/p2012712.jcwx?filterid=c2608u0j1

couple options. I would run a 12 gauge hot from the battery or + terminal block with a fuse and relay at front run to the back and ground the heater locally in the trunk with a clean solid ground using 12 gauge. Voltage drop on single 12 gauge wire at 14 amps at 15 feet is about .35v if you start with 13V and ground it locally. Should keep the heat flowing and blowing.
 
Experience tells me you need more than 90 watts.

I can do a reliable 240 watt 14v heater in a tube about 9 inches long. If you want to mount a tube heater, and use a flex hose in, and a second one out to the duct it would work.

What diameter is the duct tube?

B.
 
Hi bohica2xo, are you talking about making a tube pipe with a heater inside with a fan or w/o fan?

Are you fabricating this from scratch hypothetically?

12vdc production units are designed for RVs and auto usage so failure due to vibration, over temp conditions and burning a vehicle down are taken into consideration in the design.

What I linked has 168 watts at 12vdc probably be running at 12.5v, so about 175 watts and contains a thermal protection circuit.

Here is a 200 watt 12vdc ceramic heater tube unit also ready to rock:

http://tweetys.com/ceramicheater12v200w.aspx?gclid=CJXFhpySka4CFQ5_hwodjiCrgQ

both units cost less than 30 bucks.



bohica2xo said:
Experience tells me you need more than 90 watts.

I can do a reliable 240 watt 14v heater in a tube about 9 inches long. If you want to mount a tube heater, and use a flex hose in, and a second one out to the duct it would work.

What diameter is the duct tube?

B.
Click to expand...
 
Just a reminder, that figures up around 200-250 watts at 12-14V is one HELL of a lot of current, approaching 20A. Your old Mopar ammeter/ bulkhead circuit may not/ probably won't put up with that on top of the fuel pump, fans, stereo, heater, lights, etc etc etc that is already in use

And of course you'll need a nice big high output alternator.

Ford / Lincoln used to make a deal where the defroster was fed directly off the 3 phase stator output, which did not "go through" the rest of the system, fed the defroster directly. I have no idea how reliable they were................
 
'273:

Both Ford & Cadillac did that electric defrost with the 3 phase connection. I still have CS144 alternators on the shelf with the 3 phase connector on the back. It was an elegant solution, because it kept that load off of the rectifiers.

A 20 amp heater for a rear defogger should be wired straight from the battery with a relay at the heater & a fuse or breaker at the battery. Most OEM systems draw more than that, and are in cars with alternators three times the output of that ancient mopar design. I would plan on upgrading the alternator for a whole lot of reasons, but that is another thread.

Rice:

You seem to be making a lot of assumptions.
None of the 20 buck chinese crap has any sort of thermal protection. They don't care about your car, and warn you to "unplug the unit when not in use" . One of those links is a hair dryer. Do you really think it was designed to run more than 5 minutes at a stretch?

If you really only want to spend 20 bucks on the solution, the next time you are at Harbor Freight:

http://www.harborfreight.com/12-volt-rubberized-heater-with-fan-96144.html

It is the same as one of your links. Go plug it in, and see how hot the cord gets after 5 minutes. That should tell you about the rest of the quality.

B.
 
bohica2xo said:
If you really only want to spend 20 bucks on the solution, the next time you are at Harbor Freight:

http://www.harborfreight.com/12-volt-rubberized-heater-with-fan-96144.html

It is the same as one of your links. Go plug it in, and see how hot the cord gets after 5 minutes. That should tell you about the rest of the quality.

B.
Click to expand...

Yeah, follow that link and read some of the reviews. Some of them are pretty funny

Even one guy who claimed to be a HF "junkie" didn't like it!!!
 
Yes I would assume a production piece has thermal protection. I agree that cheap china man product may suck.
The inference is: get something with thermal protection.
Wiring with 12 gauge, fuse and relay off battery or terminal post was entailed.
:)
I mean we are not engineering systems with all certifications here, we are suggesting processes which the integrator has to use his own diligence as a final determination of viability.
 
Not an inference from you kid, but a straight up statement:

12vdc production units are designed for RVs and auto usage so failure due to vibration, over temp conditions and burning a vehicle down are taken into consideration in the design.

What I linked has 168 watts at 12vdc probably be running at 12.5v, so about 175 watts and contains a thermal protection circuit.
Click to expand...

Unless you have had one of those heaters apart, you can't say they do contain a thermal protection device. I have in fact had one apart. There is no such device installed.

The DCR on the heating element is 1.73 ohms @ 70f It climbs rapidly to 3.1 ohms at 130f - Which works out to 63 watts @ 14.0v

That would be 63 watts if it could actually see 14v - the 20ga wire in the cord provides additional ballast by warming to the touch quickly. There is a 15 amp fuse in a fuse holder, and it would probably not blow until the cord melted completely - the fuse is cool to the touch while the cord is hot. The damn thing is a fire hazard.

The little squirrel cage blower inside is rated 3.6w, and would probably be inadequate to cool the CPU in an old 386. A six year old kid with a toilet paper tube could blow a better stream of air.

A proper ruggedized ceramic element in the 250w range costs significantly more than that unit.

.
 
Bohica, Yea you're right, I should have said "should typically be designed" rather than "are designed".

You gave alot of detailed information about heating elements and fans . Is that information specifically accurate to the models of heaters I linked to? Sounds like some generalizations based on assumed design to me. Unless you have had those particular exact models apart and tested, you are only making educated speculation. Granted it sounds more educated than my speculation, so kudos to you Sir or Ma'am.
 
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