Maker Pro
Maker Pro

attic exhaust

D

Dodo

Jan 1, 1970
0
I'd like to use a solar panel to run two AC 3.4amp attic exhaust fans. What
sort of components would I need to do this? I know I'd need the panel and an
inverter, but I'm not sure if I'd need anything else. I'd also appreciate
advice on exactly what models of equipment would suit my needs.
 
K

Kevin M

Jan 1, 1970
0
That's a question I've been wanting to learn about, too, but most of
the fans seem to be 24VDC rather than AC. There are commercial
systems available for 3-400 $US, and I haven't been able to see a way
to build one for less than $200. Assuming I could figure out the
amps, volts, etc.
 
J

Joe Fischer

Jan 1, 1970
0
: That's a question I've been wanting to learn about, too, but most of
: the fans seem to be 24VDC rather than AC.

Which makes sense for the following reason;

AC motors will be damaged by voltage less than rated,

while DC motors will just rotate slower at lower voltages
without overheating or damage. (There are many types
of motors, but DC motors commonly have brushes and either
a slip ring with small brushes carrying the field current
to the rotor, or have large brushes carrying the armature
current).

There are many low cost motors, mostly 12 volt
in auto junk yards, they are the heater and air
conditioner fan motors.
They are attached to squirrel cage blowers,
which may not be high volume fans.

Some of them have permanent magnetic stators
with rotating field coils and small brushes.
The squirrel cage blowers do have a disadvantage
of being noisy.

There are also DC motors used for radiator
fans for many newer cars, and that have regular
fan blades.

Any of these, 12 volt or 24 volt from trucks
or RVs, could be used with just diodes and solar
panels provided they are fused to protect in case
of bearing failure.
The most destructive problem with motors is
that the bearings bind up and lock the rotor, which
often means the motor overheats, smokes badly, and
burns the windings out if not fused.

The good thing is that 12 volt panels can
be used with either 12 or 24 volt motors if wired
correctly.
The permanent motor in my cars draws a lot
of amps, at least 10 or more. This is not near
the equivalence of 3.4 amps on 120 volts, but it
is considerable.

The radiator fan motors would be easier to
use for ventilation because they have the right
type of fan blade already installed and may have
the motor support bracket.
But more than one or two may be needed,
although any ventilation on a hot sunny day
will provide some comfort, lower cooling bills
and help protect the roofing materials from
drying out.

Joe Fischer
 
S

SpiderG

Jan 1, 1970
0
Do a Google search for solar attic fans - I got dozens of hits for both
through the roof setups and gable end versions. Some can be outfitted with a
klixon temp switch too (makes sense for winter use).

I personally put a through the roof unit in a few weeks ago. Although a
little pricey, it only took 30 min. on the roof - and no power cords to run.

Good Luck!

SpiderG
 
N

Nick Pine

Jan 1, 1970
0
Bill Kaszeta / Photovoltaic Resources said:
The standard ac motors used in the attic fans are very low efficiency
"shaded-pole" ac motors.

There's also much to be said for low and high vents, with no motors.

Nick
 
W

Watson A.Name - 'Watt Sun'

Jan 1, 1970
0
I'd like to use a solar panel to run two AC 3.4amp attic exhaust fans. What
sort of components would I need to do this? I know I'd need the panel and an
inverter, but I'm not sure if I'd need anything else. I'd also appreciate
advice on exactly what models of equipment would suit my needs.

It seems to me that using an AC motor with an inverter is wasting a
good percentage of the power. I would use the 12VDc off the panels
with a DC motor such as the fan motor from a front wheel drive car, or
maybe one even more powerful than that. Also, if the panel isn't
getting full sunlight, then the DC motor might run at half speed,
where the inverter might not run the AC motor at all.

Oh, one other thing. It seems that a convection system might be the
way to go with this attic ventilation. And also there are those wind
turbines that run off convection.

--
@@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@h@e@r@e@@
###Got a Question about ELECTRONICS? Check HERE First:###
http://users.pandora.be/educypedia/electronics/databank.htm
My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you add NOSPAM in the
Subject: line with other stuff. alondra101 <at> hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html
@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@
 
W

Watson A.Name - 'Watt Sun'

Jan 1, 1970
0
Ah yes. Winter.

Well, this is San Diego, so...

I'm just up the road, a few miles from Dizzyland, and I know what you
mean. But I still see houses with bags over the wind turbines in
"winter" around here. Probably doesn't make a lotta diff on the
heating bill.


--
@@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@h@e@r@e@@
###Got a Question about ELECTRONICS? Check HERE First:###
http://users.pandora.be/educypedia/electronics/databank.htm
My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you add NOSPAM in the
Subject: line with other stuff. alondra101 <at> hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html
@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@
 
J

Joe Fischer

Jan 1, 1970
0
: It seems to me that using an AC motor with an inverter is wasting a
: good percentage of the power. I would use the 12VDc off the panels
: with a DC motor such as the fan motor from a front wheel drive car, or
: maybe one even more powerful than that. Also, if the panel isn't
: getting full sunlight, then the DC motor might run at half speed,
: where the inverter might not run the AC motor at all.

And there are millions of them junked every year,
even with the shroud just like an attic fan.
Some of them have a Sprague bearing clutch on
the fan blade that lets it freewheel if the wind blows,
reducing power consumption.

Joe Fischer
 
K

Kevin M

Jan 1, 1970
0
That does sound like a great idea -- get a fan assembly from a junked
car (assuming it was rear-ended, of course :) ).

For those of us who are total solar neophytes, can you help me with my
math:

example fan motor from http://www.spal-usa.com/pdfs/10Fans.pdf (an
after-market fan manufacturer):

12V
10 - 14.7A

Watts = V x A

Watts = 12 x 14.7 = 176.4 W

As this thing would run primarily during the daylight, a battery
doesn't seem as logical as a direct-powered system. How much solar
cell would you need to drive a 180W motor?
 
S

Steve Spence

Jan 1, 1970
0
as you are interested in running this only when the sun shines, and don't
need battery storage, the panel wattage has to exceed the motor wattage, so
anything over 200 watts of pv will work fine. one issue is cloud cover. the
roof will still gain heat, but solar generation will be off. maybe 350ah
battery storage, four 100 watt panels and a thermostat are not a bad idea.
pretty expensive compared to a turbine, or soffit vents with a ridge vent.
 
K

Kevin M

Jan 1, 1970
0
That's what I was thinking -- they sell commercial versions at Lowe's
for around $300 -- I'm sure there are ways to find more efficient
motors, etc., but PV doesn't seem economically viable if you have any
other source of power. More's the pity -- an attic fan seems like the
perfect application of PV technology.
 
Top