multi-speed furnace blower motor

Discussion in 'Home Power and Microgeneration' started by Dave, Sep 24, 2008.

  1. Dave

    Dave Guest

    First off, I have no idea if this is an inappropriate forum for this
    question, so please redirect me if there is a better group for this.

    I've got an old (1970's) gas-fired forced-air furnace in my basement. It
    has, as one might expect, a single-speed fan motor. The motor is a 1725rpm
    1/4hp. During the winter we heat primarily with wood. We have a woodstove
    in the livingroom, and for the past few years have turned the furnace fan on
    during the day to circulate the heat to the rest of the house. We plug the
    cold-air intake during the winter, because otherwise we get outside-temp air
    mixed with the recirculated air which can have more of a cooling than
    heating effect when it's 0F outside. The house is >60 years old and has
    plenty of air leaks already, so please don't bother warning me about
    plugging the cold air intake... we've been doing it for years and nothing's
    broken down and everybody's still alive.

    I'd like to switch my fan motor to a two-speed for a number of reasons. It
    will allow me to re-connect the cold air intake to the furnace, it will
    lower my electricity costs as I don't need the furnace fan on full speed
    just to keep heat ciruclating, etc. The problem is that the only motors I
    see available are 1725/1140rpm motors. 1140rpm is too fast for me, and will
    definitely still pull in too much cold air, plus I doubt I'll save that much
    $$ using it. I was thinking more like 500rpm.

    So, first off I'd like to know if anyone knows of a manufacturer (and even
    better a retailer) who sells such a motor? I have been perusing the
    internet for an hour and while I see references to multi-speed FURNACES I
    don't see any mutli-speed motors for sale (other than the aforementioned
    1725/1140 motors).

    Secondly, how do the multi-speed newer furnaces which run at a low speed all
    or most of the time deal with the cold-air intake issue?

    I don't want to invest a pile of money in this ancient furnace, which would
    preclude any type of microprocessor-controlled, sensor-driven,
    cfm-regulated, variable-speed ECM motor system... I just want a two-speed
    fan to circulate the air and not pull cold air into the house and which
    switches to high speed when the thermostat kicks the furnace on.

    Thanks in advance for any replies.

    Dave
    British Columbia, Canada
    Dave, Sep 24, 2008
    #1
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  2. Dave

    Dave Guest

    "Neon John" <> wrote in message
    news:...
    > On Wed, 24 Sep 2008 18:12:57 GMT, "Dave" <> wrote:
    >
    >
    > The usual place for a replacement motor is a motor repair shop or
    > appliance
    > parts warehouse or last resort, an HVAC wholesaler. The latter will
    > charge
    > you the 'walk-in' price which is double the trade price.
    >
    > The most speeds I've seen is 5. Most general purpose replacement fan
    > motors
    > are 4 speed. The installer chooses the speed that best fits the air
    > handler.
    > The idea is to only have to carry a few part numbers on the service truck.
    >


    Thanks a lot for all of the information. I went to my local motor repair
    shop, and they tried to tell me that an 1140/1725 was all that was
    available. Maybe I'll try another shop.

    > If you can't find anyone else, you can call the place where I occasionally
    > moonlight, Jerry's Electric Motor Service in Cleveland, TN, 423 472-5959.
    > Jerry Brown (Sr and Jr) operate the place. They ship UPS all over the
    > country. You'll need the following when you call: ALL the nameplate
    > data.
    > the shaft diameter. Whether the shaft is round or has a flat machined on
    > it.
    > How it mounts (by the frame bolts or via clamp rings.) Figure about $80.
    >
    > Most permanent capacitor run fan motors (most likely what you have) can be
    > slowed with an SCR light dimmer. The dimmer must be a commercial version
    > that
    > can handle inductive loads. I use the commercial grade Lutron dimmers
    > that
    > Home Depot sells. I have a squirrel cage fan mounted on a tripod that I
    > use
    > for comfort cooling in my shop. The dimmer lets me vary the speed. I use
    > a
    > combination of speed and intake blocking to get the amount of air I need.
    >


    My fan is mounted inside the back of the furnace, and there is a filter just
    above the fan. I could very easily cut a piece of cardboard the same size
    as the filter and make a hole in it to only let a portion of air through.
    This will do what I want as far as restricting the air flow, but may present
    problems when the furnace turns on as I'd conceivably have much less
    efficient distribution of the heated air and more wasted heat up the chimney
    if I'm not getting my flow through the heat exchanger. In addition, as you
    note I may run into a motor overtemp situation.

    I like the SCR dimmer idea... does the dimmer dissipate the dropped power
    via heat? I am thinking that I could wire the dimmer in via a relay, so
    that when the furnace kicks on, the relay coil energizes and cuts the dimmer
    out of the circuit resulting in high speed. Do you see anything wrong with
    this approach?

    Why would anyone buy a new 2-speed motor if they could use a cheap dimmer
    and relay?

    > Another way to slow the motor is to place an appropriate value of motor
    > run
    > capacitor in series with one power lead. One can compute the size but
    > it's
    > easier to just try a few until you get the speed you want. If this is a
    > 120
    > volt fan, I'd guesstimate about a 40uF unit to start.
    >


    Same concerns as above. It Would be pretty easy though. Is the idea that
    the capacitor introduces phase shift which makes the motor less efficient?
    My understanding of capacitors is that they pass AC with minimal power loss,
    otherwise they'd be hot all the time, which they are not.

    >>
    >>Secondly, how do the multi-speed newer furnaces which run at a low speed
    >>all
    >>or most of the time deal with the cold-air intake issue?

    >
    > It's not the cold air intake that is an issue. The issue is pushing
    > heavier,
    > denser cold air through the duct work in the summer time. That's why dual
    > speed fans run faster on AC than when heating.
    >


    Just to clarify (you probably already figured this, but I'll state it just
    to be clear) my house has a duct system for heated air, and a separate
    system for cold air return. Each room in the house has two ducts, on
    opposite sides of the room in most cases. The cold air return duct system
    leads to the furnace and connects right above the filter and (below that)
    the fan and motor. There is a duct which runs from the outside of the house
    and connects to the cold air return ducting just prior to the furnace.

    When I run JUST THE FAN in the winter time, with the outside air duct open,
    it blows COLD AIR in my house, at least a whole lot colder than the ambient
    air inside the house. I don't know why this would be. The house is old,
    and the doors and windows probably do leak A BIT, but I'd think a fair
    amount of cold air needs to be being pulled in to feel as cold as it does.

    > John
    > --
    > John De Armond
    > See my website for my current email address
    > http://www.neon-john.com
    > http://www.johndearmond.com <-- best little blog on the net!
    > Tellico Plains, Occupied TN
    > To have doubted one’s own first principles is the mark of a civilized
    > man -Oliver Wendell Holmes Jr.
    >
    Dave, Sep 24, 2008
    #2
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  3. Dave

    Dave Guest

    "Don Young" <> wrote in message
    news:...
    >
    > You already have lots of good advice but your inability to find the motor
    > you want is probably because you have only looked at 2 speed motors. It
    > makes sense that a 1725 RPM (4 pole) motor would be unlikely to have
    > anything except about 1140 RPM (6 poles) as its second speed. For lower
    > speeds you could just get a 3 or 4 speed motor. There are a lot of
    > variable speed motors used in HVAC systems but they often have rather
    > complicated controls and high costs.
    >
    > Don Young
    >

    Ahhh, yes. It can be challenging figuring out the right question to ask!
    Needing only two speeds, that's what I searched for. I think I will try the
    SCR idea for now as it's likely cheaper than any motor I could source. In
    addition I won't have to deal with mounting a motor with a different
    footprint than the one I'm replacing. I looked at various systems, ECM
    motors, etc. but really don't want to put hundreds of dollars into this old
    furnace.

    Thanks for the reply.

    Dave
    Dave, Sep 25, 2008
    #3
  4. Dave

    Dave Guest

    "Neon John" <> wrote in message
    news:...
    > On Wed, 24 Sep 2008 22:02:04 GMT, "Dave" <> wrote:
    >

    into a motor overtemp situation.
    >>
    >>I like the SCR dimmer idea... does the dimmer dissipate the dropped power
    >>via heat? I am thinking that I could wire the dimmer in via a relay, so
    >>that when the furnace kicks on, the relay coil energizes and cuts the
    >>dimmer
    >>out of the circuit resulting in high speed. Do you see anything wrong
    >>with
    >>this approach?

    >
    > That should work.
    >>

    > Capacitive reactance is used to limit current and drop voltage in a wide
    > variety of consumer electronic gadgets. An example is something we talk
    > about
    > a lot here - the Kill-A-Watt. There is a large cap in series with a low
    > value
    > resistor that supplies power directly from the line to the voltage
    > regulator.
    >
    > Another example is the Bosch cordless drill battery charger from a few
    > years
    > ago. The charger seems too light weight to have anything inside. I had
    > one
    > of those drills and when I opened the charger case, found little more than
    > a
    > large cylindrical polypropylene cap in series with the line. IT worked
    > well,
    > as I had that drill for almost a decade before the batteries finally
    > crapped
    > out.
    >


    Capacitive reactance is one of those terms I find tough to get a handle on.
    I repair electronic equipment as a hobby, and have (started to) read many
    books on electronics theory. Phase angle and capacitive reactance have
    never been clear though. You know the old first law of thermodynamics:
    energy is neither created nor destroyed, simply made to change forms.
    Resistors drop voltage, they get hot. (linear) voltage regulators drop
    voltage, they get hot. I can see where logic-based switching circuits, like
    PWM's, can vary voltage by switching, similar to an SCR so that less power
    is let through the circuit rather than having to dissipate excess. But
    capacitive reactance dropping voltage... where does the extra power go? I
    look at capacitors like voltage reservoirs, but I guess they are current
    limiters as well seen from a different angle.

    > Let's clarify terminology.
    > Separate from those, some systems have an intake for outside air,
    > variously
    > called a fresh air intake or tempering air intake. In the past a fresh
    > air
    > intake was used to supply what turned out to be an overabundance of fresh
    > air.
    > Research showed that the interior could be maintained comfortable with
    > much
    > fewer air exchanges than previously believed. Your system is old enough
    > to
    > have been installed during that era.
    >


    Yah, I used the term "cold air" instead of "fresh air".

    > Anyway, back to your situation. A house that old probably does NOT need
    > the
    > fresh air intake that you have. Unless you get a CO buildup from the wood
    > furnace, you can safely block it during heating season. You could
    > manually
    > cut it in during mild weather when the outside air is more comfortable
    > than
    > inside. Or you could get one of those little computer modules and a
    > couple of
    > damper drive motors and automate the process.
    >

    I've got wood-frame single-pane windows, for which I have built single-pane
    wood-frame storm windows. I seal the be-jesus out of them in the fall,
    using a product called "draft stop" which is a removable (doesn't exactly
    come off like they show in the commercial but...) silicone sealant around
    the outside of the inner windows and closed-cell foam around the edges of
    the storms. But I still get condensation between the storm and inner
    windows in the winter. It's been suggested to me that if I ran the fan 24/7
    on slow speed, with a fresh air intake connected, that I'd create a positive
    pressure inside the house which would tend to push dry air into the airspace
    between the windows rather than drawing cooler wet air in from outside. I
    have no idea if a) this is true or b) if this is attainable. Right now my
    fresh air intake is a 4" duct. Maybe if I damped this down (manual-style,
    stick a bat of insulation into it or something like that) it would help
    mitigate the seemingly excess amount of cold air drawn in to the return
    system.

    Again, many thanks for your time and expertise.

    Dave
    Dave, Sep 25, 2008
    #4
  5. Dave <> wrote:
    >
    > "Neon John" <> wrote in message
    > news:...
    >> On Wed, 24 Sep 2008 22:02:04 GMT, "Dave" <> wrote:
    >>

    > into a motor overtemp situation.
    >>>
    >>>I like the SCR dimmer idea... does the dimmer dissipate the dropped power
    >>>via heat? I am thinking that I could wire the dimmer in via a relay, so
    >>>that when the furnace kicks on, the relay coil energizes and cuts the
    >>>dimmer
    >>>out of the circuit resulting in high speed. Do you see anything wrong
    >>>with
    >>>this approach?

    >>
    >> That should work.
    >>>

    >> Capacitive reactance is used to limit current and drop voltage in a wide
    >> variety of consumer electronic gadgets. An example is something we talk
    >> about
    >> a lot here - the Kill-A-Watt. There is a large cap in series with a low
    >> value
    >> resistor that supplies power directly from the line to the voltage
    >> regulator.
    >>
    >> Another example is the Bosch cordless drill battery charger from a few
    >> years
    >> ago. The charger seems too light weight to have anything inside. I had
    >> one
    >> of those drills and when I opened the charger case, found little more than
    >> a
    >> large cylindrical polypropylene cap in series with the line. IT worked
    >> well,
    >> as I had that drill for almost a decade before the batteries finally
    >> crapped
    >> out.
    >>

    >
    > Capacitive reactance is one of those terms I find tough to get a handle on.
    > I repair electronic equipment as a hobby, and have (started to) read many
    > books on electronics theory. Phase angle and capacitive reactance have
    > never been clear though. You know the old first law of thermodynamics:
    > energy is neither created nor destroyed, simply made to change forms.
    > Resistors drop voltage, they get hot. (linear) voltage regulators drop
    > voltage, they get hot. I can see where logic-based switching circuits, like
    > PWM's, can vary voltage by switching, similar to an SCR so that less power
    > is let through the circuit rather than having to dissipate excess. But
    > capacitive reactance dropping voltage... where does the extra power go? I
    > look at capacitors like voltage reservoirs, but I guess they are current
    > limiters as well seen from a different angle.


    If you look at capacitors similar to a lead acid battery it makes a bit
    more sense for AC.

    Say you connect a 400uF cap across 120 volts.

    It will charge up to a peak of around 180 or whatever. It just stored a
    charge.

    Now the as the line voltage drops towards 0 and reverses, it's going to
    dump current back into the outlet, like a battery would. It's giving back
    what it took. This process of take some energy, then give it back keeps
    repeating.

    If you connect a current meter across a lead of this cap, you'd measure
    some amps of current flowing, but considering that it's not really using
    up much power (just it's internal losses which are really low for film cap
    of that size) no work is being done and the power draw is almost nothing.

    It obviously gets more complex when you deal with phase shifts or some
    inductance added into the mix, but a capacitor itself is more like a
    spring of sorts. It can store energy, but it has to dump it somewhere
    before it can store a new charge. resistors can dissipate energy, but
    store nothing.
    Cydrome Leader, Sep 25, 2008
    #5
  6. Dave

    daestrom Guest

    Don Young wrote:
    > "Dave" <> wrote in message
    > news:JqvCk.1741$T65.602@edtnps82...
    >> First off, I have no idea if this is an inappropriate forum for this
    >> question, so please redirect me if there is a better group for this.
    >>
    >> I've got an old (1970's) gas-fired forced-air furnace in my
    >> basement. It has, as one might expect, a single-speed fan motor. The
    >> motor is a 1725rpm 1/4hp. During the winter we heat primarily
    >> with wood. We have a woodstove in the livingroom, and for the past
    >> few years have turned the furnace fan on during the day to circulate
    >> the heat to the rest of the house. We plug the cold-air intake
    >> during the winter, because otherwise we get outside-temp air mixed
    >> with the recirculated air which can have more of a cooling than
    >> heating effect when it's 0F outside. The house is >60 years old
    >> and has plenty of air leaks already, so please don't bother warning
    >> me about plugging the cold air intake... we've been doing it for
    >> years and nothing's broken down and everybody's still alive. I'd like to
    >> switch my fan motor to a two-speed for a number of
    >> reasons. It will allow me to re-connect the cold air intake to the
    >> furnace, it will lower my electricity costs as I don't need the
    >> furnace fan on full speed just to keep heat ciruclating, etc. The
    >> problem is that the only motors I see available are 1725/1140rpm
    >> motors. 1140rpm is too fast for me, and will definitely still pull
    >> in too much cold air, plus I doubt I'll save that much $$ using it. I was
    >> thinking more like 500rpm. So, first off I'd like to know if anyone knows
    >> of a manufacturer
    >> (and even better a retailer) who sells such a motor? I have been
    >> perusing the internet for an hour and while I see references to
    >> multi-speed FURNACES I don't see any mutli-speed motors for sale
    >> (other than the aforementioned 1725/1140 motors).
    >>
    >> Secondly, how do the multi-speed newer furnaces which run at a low
    >> speed all or most of the time deal with the cold-air intake issue?
    >>
    >> I don't want to invest a pile of money in this ancient furnace, which
    >> would preclude any type of microprocessor-controlled, sensor-driven,
    >> cfm-regulated, variable-speed ECM motor system... I just want a
    >> two-speed fan to circulate the air and not pull cold air into the
    >> house and which switches to high speed when the thermostat kicks the
    >> furnace on. Thanks in advance for any replies.
    >>
    >> Dave
    >> British Columbia, Canada

    > You already have lots of good advice but your inability to find the
    > motor you want is probably because you have only looked at 2 speed
    > motors. It makes sense that a 1725 RPM (4 pole) motor would be
    > unlikely to have anything except about 1140 RPM (6 poles) as its
    > second speed.


    Having rewound more than a few induction motors, I can tell you it is very
    easy to wind a 4-pole motor and reconnect it for 8 poles (~900 RPM) *if* the
    connections between poles are brought out to the terminal head (one
    connection commonly used is called 'consequent pole', but it comes in three
    variations, a fan application would use "variable torque / variable power"
    connection). To get 4 and 6 poles takes two separate windings that is
    harder and costlier.

    Using a dimmer on anything but the smallest of induction motors is asking
    for trouble. Running induction motors on less than their rated voltage is a
    pretty sure-fire way to burn them out. Same with putting a cap in series
    with the line, it does the same thing and reduces the terminal voltage to
    the motor.

    A 'throttle plate' would work well so long as the OP doesn't have to run the
    furnace with the throttle plate installed. If the furnace runs with too
    little air flow, the heat-exchanger safety switch will trip when the
    heat-exchanger hood overheats from a lack of air flow.

    daestrom
    daestrom, Sep 25, 2008
    #6
  7. Dave

    Dave Guest

    "Neon John" <> wrote in message
    news:...
    > On Thu, 25 Sep 2008 16:55:07 -0400, "daestrom"
    > <daestrom@NO_SPAM_HEREtwcny.rr.com> wrote:
    >
    >
    >>Using a dimmer on anything but the smallest of induction motors is asking
    >>for trouble. Running induction motors on less than their rated voltage is
    >>a
    >>pretty sure-fire way to burn them out. Same with putting a cap in series
    >>with the line, it does the same thing and reduces the terminal voltage to
    >>the motor.

    >
    > Shhhh. Please don't tell all the motors around my place that are running
    > on
    > dimmers and/or capacitors that! The might go on strike or something.
    > This
    > includes the 3/4 hp squirrel cage fan that constitutes my whole house fan.
    > Or
    > the 1 hp gear motor on my BBQ sauce mixer. Yep, another Lutron dimmer
    > controlling it.
    >
    > How's that old saying go? "Those who say it can't be done should stand
    > aside
    > so as not to obstruct those of us who are doing it."
    >
    > There ARE some single phase motors that simply cannot be slowed with a
    > phase
    > angle controller but they aren't used in furnace blowers and so there is
    > no
    > need to muddy the water with those details.
    >


    Okay, one more question regarding phase angle controllers and AC induction
    motors: Is the amount of strain which the use of an SCR puts on a motor
    proportional to the voltage drop? Because I'd want to use this dimmer to
    run the fan SLOW, probably a couple of hundred RPM's. Common sense (well,
    my common sense anyway) warns that whereas slowing it from 1725 to 1500 RPMs
    won't stress the motor significantly, maybe 400 RPMs would. Am I wrong?
    Dave, Sep 26, 2008
    #7
  8. Dave

    daestrom Guest

    Neon John wrote:
    > On Thu, 25 Sep 2008 16:55:07 -0400, "daestrom"
    > <daestrom@NO_SPAM_HEREtwcny.rr.com> wrote:
    >
    >
    >> Using a dimmer on anything but the smallest of induction motors is
    >> asking for trouble. Running induction motors on less than their
    >> rated voltage is a pretty sure-fire way to burn them out. Same with
    >> putting a cap in series with the line, it does the same thing and
    >> reduces the terminal voltage to the motor.

    >
    > Shhhh. Please don't tell all the motors around my place that are
    > running on dimmers and/or capacitors that! The might go on strike or
    > something. This includes the 3/4 hp squirrel cage fan that
    > constitutes my whole house fan. Or the 1 hp gear motor on my BBQ
    > sauce mixer. Yep, another Lutron dimmer controlling it.
    >
    > How's that old saying go? "Those who say it can't be done should
    > stand aside so as not to obstruct those of us who are doing it."


    And if you don't know what you're doing, just jury-rig the heck out of it
    and claim success.

    >
    > There ARE some single phase motors that simply cannot be slowed with
    > a phase angle controller but they aren't used in furnace blowers and
    > so there is no need to muddy the water with those details.


    Induction motors of any size can be burned out when run on lower than rated
    voltage. It's a simple fact. Ever have to replace a 'fridge compressor
    because of low line voltage? How about the 'acrid odor' from a burned out
    blower motor?

    Squirrel cage induction motors only slow down on low voltage because they
    can't develop enough torque and the current draw goes up considerably. Now,
    universal motors on a dimmer, that's fine. Hook a dimmer up to the blower
    motor of your furnace and it will most likely burn up.

    A 1 hp gear motor for a sauce mixer? LOL. if the speed varies widely with
    voltage, it probably isn't a squirrel cage motor in the first place.

    Let's see if some EE's in alt-engineering-electrical think your idea is
    worthwhile. Don, Charles, what do you think of using a dimmer to slow down
    a furnace blower?

    daestrom
    daestrom, Sep 27, 2008
    #8
  9. Dave

    daestrom Guest

    Dave wrote:
    > "Neon John" <> wrote in message
    > news:...
    >> On Thu, 25 Sep 2008 16:55:07 -0400, "daestrom"
    >> <daestrom@NO_SPAM_HEREtwcny.rr.com> wrote:
    >>
    >>
    >>> Using a dimmer on anything but the smallest of induction motors is
    >>> asking for trouble. Running induction motors on less than their
    >>> rated voltage is a
    >>> pretty sure-fire way to burn them out. Same with putting a cap in
    >>> series with the line, it does the same thing and reduces the
    >>> terminal voltage to the motor.

    >>
    >> Shhhh. Please don't tell all the motors around my place that are
    >> running on
    >> dimmers and/or capacitors that! The might go on strike or something.
    >> This
    >> includes the 3/4 hp squirrel cage fan that constitutes my whole
    >> house fan. Or
    >> the 1 hp gear motor on my BBQ sauce mixer. Yep, another Lutron
    >> dimmer controlling it.
    >>
    >> How's that old saying go? "Those who say it can't be done should
    >> stand aside
    >> so as not to obstruct those of us who are doing it."
    >>
    >> There ARE some single phase motors that simply cannot be slowed with
    >> a phase
    >> angle controller but they aren't used in furnace blowers and so
    >> there is no
    >> need to muddy the water with those details.
    >>

    >
    > Okay, one more question regarding phase angle controllers and AC
    > induction motors: Is the amount of strain which the use of an SCR
    > puts on a motor proportional to the voltage drop? Because I'd want
    > to use this dimmer to run the fan SLOW, probably a couple of hundred
    > RPM's. Common sense (well, my common sense anyway) warns that
    > whereas slowing it from 1725 to 1500 RPMs won't stress the motor
    > significantly, maybe 400 RPMs would. Am I wrong?


    I'd say you are correct. But Neon seems to think you can do it (of course,
    he's jury-rigged a lot of things). Try it and when it burns out, send him
    the bill.

    daestrom
    daestrom, Sep 27, 2008
    #9
  10. Dave

    daestrom Guest

    Neon John wrote:
    > On Thu, 25 Sep 2008 16:55:07 -0400, "daestrom"
    > <daestrom@NO_SPAM_HEREtwcny.rr.com> wrote:
    >
    >
    >> Using a dimmer on anything but the smallest of induction motors is
    >> asking for trouble. Running induction motors on less than their
    >> rated voltage is a pretty sure-fire way to burn them out. Same with
    >> putting a cap in series with the line, it does the same thing and
    >> reduces the terminal voltage to the motor.

    >
    > Shhhh. Please don't tell all the motors around my place that are
    > running on dimmers and/or capacitors that! The might go on strike or
    > something. This includes the 3/4 hp squirrel cage fan that
    > constitutes my whole house fan. Or the 1 hp gear motor on my BBQ
    > sauce mixer. Yep, another Lutron dimmer controlling it.
    >
    > How's that old saying go? "Those who say it can't be done should
    > stand aside so as not to obstruct those of us who are doing it."


    And then there are those of us that spent more than a few years in motor
    re-wind shop, fixing burned out motors and re-winding them. I've had a few
    customers that burned out their motor and was surprised when I told them it
    wasn't worth rewinding but they should buy a new one and run it at the
    proper voltage.

    >
    > There ARE some single phase motors that simply cannot be slowed with
    > a phase angle controller but they aren't used in furnace blowers and
    > so there is no need to muddy the water with those details.


    Certainly *my* furnace blower is in that category. But then a lot of them
    are internally protected so they'll just shut themselves down when they
    start to overheat. The user may wonder why it stops and then restarts after
    cooling.

    daestrom
    daestrom, Sep 27, 2008
    #10
  11. Dave

    Don Kelly Guest

    ----------------------------
    "daestrom" <daestrom@NO_SPAM_HEREtwcny.rr.com> wrote in message
    news:...
    > Neon John wrote:
    >> On Thu, 25 Sep 2008 16:55:07 -0400, "daestrom"
    >> <daestrom@NO_SPAM_HEREtwcny.rr.com> wrote:
    >>
    >>
    >>> Using a dimmer on anything but the smallest of induction motors is
    >>> asking for trouble. Running induction motors on less than their
    >>> rated voltage is a pretty sure-fire way to burn them out. Same with
    >>> putting a cap in series with the line, it does the same thing and
    >>> reduces the terminal voltage to the motor.

    >>
    >> Shhhh. Please don't tell all the motors around my place that are
    >> running on dimmers and/or capacitors that! The might go on strike or
    >> something. This includes the 3/4 hp squirrel cage fan that
    >> constitutes my whole house fan. Or the 1 hp gear motor on my BBQ
    >> sauce mixer. Yep, another Lutron dimmer controlling it.
    >>
    >> How's that old saying go? "Those who say it can't be done should
    >> stand aside so as not to obstruct those of us who are doing it."

    >
    > And if you don't know what you're doing, just jury-rig the heck out of it
    > and claim success.
    >
    >>
    >> There ARE some single phase motors that simply cannot be slowed with
    >> a phase angle controller but they aren't used in furnace blowers and
    >> so there is no need to muddy the water with those details.

    >
    > Induction motors of any size can be burned out when run on lower than
    > rated voltage. It's a simple fact. Ever have to replace a 'fridge
    > compressor because of low line voltage? How about the 'acrid odor' from a
    > burned out blower motor?
    >
    > Squirrel cage induction motors only slow down on low voltage because they
    > can't develop enough torque and the current draw goes up considerably.
    > Now, universal motors on a dimmer, that's fine. Hook a dimmer up to the
    > blower motor of your furnace and it will most likely burn up.
    >
    > A 1 hp gear motor for a sauce mixer? LOL. if the speed varies widely
    > with voltage, it probably isn't a squirrel cage motor in the first place.
    >
    > Let's see if some EE's in alt-engineering-electrical think your idea is
    > worthwhile. Don, Charles, what do you think of using a dimmer to slow
    > down a furnace blower?
    >
    > daestrom


    One can use a dimmer on an induction motor provided that the motor is
    operating below its rated and the dimmer is rated for motor operation (more
    expensive than light dimmers).
    On a fan, as the speed drops, the torque required will generally drop faster
    than the speed so a small speed change will result in a greater drop in load
    torque (and air flow) so one might get away with it without burning out the
    motor. However, trying to decrease speed this way has its limits in that
    starting can be questionable and stalling is a definite possibility. There
    are devices on the market which do this and great claims are made -but the
    downside conditions are ignored. Neon John is lucky. Ignorance is bliss in
    that case.

    The gear motor may be a "universal motor" or even a "brushless DC" motor.
    (1HP rating - pretty big compared to the average mixmaster).

    As for series capacitors- Not a good idea and the effect on terminal voltage
    will be dependent on the operating point. How close to series resonance do
    you want to go?

    I use a motor rated dimmer on a small fan motor for a fireplace- It allows
    me to set a minimum speed so that I couldn't stall the motor and it
    requires me to start the fan at full voltage.
    Would I do it with my furnace motor? No way!

    Don Kelly
    remove the X to answer

    >
    Don Kelly, Sep 27, 2008
    #11
  12. Dave

    daestrom Guest

    Neon John wrote:
    > On Fri, 26 Sep 2008 19:18:46 -0400, "daestrom"
    > <daestrom@NO_SPAM_HEREtwcny.rr.com> wrote:
    >
    >

    <snip>
    >> Let's see if some EE's in alt-engineering-electrical think your idea
    >> is worthwhile. Don, Charles, what do you think of using a dimmer to
    >> slow down a furnace blower?

    >
    > Instead of running off like a coward for reinforcements, why don't we
    > cut to the chase? Why don't you put your money where your mouth is.
    > If you're so convinced that I don't know what I'm talking about, this
    > should be a no-brainer for you.
    >


    You sound like some bully in the school yard that resorts to name-calling
    when someone disagrees with them. Real mature. Point is you won't take my
    word for it, so I simply asked that some other experts, with much more
    experience than you join in the conversation.

    It's obvious that *you* are the one that is afraid of real experts, as you
    keep dropping the alt.engineering.electrical group from the discussion. Why
    is that John, afraid someone there might actually know more about the
    subject than you?? Not to worry, I added it back for you. I've posted
    there many times over the years and found some very knowledgable folks there
    (but of course it has a few crackpots as well). My experience with rotating
    machinery has been well received there, why don't you go read some and learn
    some.

    Going to experts to solve a disagreement isn't 'running off like a coward',
    it's the smart and mature thing to do. Trying to make it look like the act
    of a coward is pretty childish.

    If you read Don's reply you'll see that his position seems somewhere in
    between ours. He points out that some loads like fans have a rapid drop in
    their power requirements at slow speeds and so the load on the motor could
    drop fast enough at slow speeds to avoid damage to the motor. So for some
    things, Don thinks a suitably rated dimmer would be okay for variable speed
    control. But he also doesn't think it would be appropriate for a furnace
    blower.

    > I have $1000 that says that I can slow most any furnace blower with
    > an SCR controller and in particular, that I can slow the one that I
    > use in my shop to circulate air. Or my heat pump's blower, provided
    > it uses a 120 volt motor (I have no idea at this point.) Your choice.
    > I'll video the whole experiment and put it on Youtube.
    >
    > "success" is defined as operating the motor over its useful speed
    > range until its temperature stabilizes with the winding temperature
    > as indicated by an attached thermocouple not exceeding its class
    > rating.


    As if your ten minute video would 'prove' anything. Just grandstanding in
    front of your admirers??

    Temperature rise in the motor is not something you can measure with a
    thermocouple attached on the outside, or even on the winding. It's internal
    to the slot where the heat has the hardest time being conducted away from
    the source. Large motors often have temperature detectors embedded in the
    winding during manufacture. Motors that are 'internally protected' often
    have the protective device embedded as well. You going to take your motor
    and unwind it to put a detector in the proper place? Better not, you
    probably wouldn't know how to re-wind it again.

    A mild case of overheating internally won't show up as a failure in an hour
    or two, or even a day. But it will shorten the life of the insulation in
    the slots and cause failure.

    >
    > Of course, if you behave as you usually do, you'll crawfish and
    > backtrack as fast as you can. A typical net.alligator - all mouth
    > and no brain. Or integrity. That's why you hide behind a nym.
    >



    Ad hominem attack, the last resort of wannabes and losers. You don't know
    why I use a nym, but you see it as point to attack, so you go for it. You
    have no way to judge my integrity, but why not attack that too?

    I haven't 'crawfished' or backtracked from you in previous arguments, yet
    you try to portray me as one who does. That's more a strawman tactic, but I
    expect about as much from you.

    > So let's see if you're a man or a mouth. Anyone want to place a side
    > bet on whether he'll do anything other than run his mouth?
    >


    Ah, trying to foment some sort of 'mob mentality'. Why don't you wrap
    yourself in the flag and blame me for all that's wrong with the world while
    you're at it. A lot of petty dictators do that. It works, for a while.

    Or you could just admit that you're just a tinkerer that plays around with
    stuff and "doesn't play well with others."

    daestrom
    daestrom, Sep 27, 2008
    #12
  13. Dave

    bw Guest

    "Neon John" <> wrote in message
    news:...
    > On Sat, 27 Sep 2008 08:50:03 -0400, "daestrom"
    > <daestrom@NO_SPAM_HEREtwcny.rr.com> wrote:
    >
    > I started to write a fact-based rebuttal to this garbage but then I
    > realized
    > that I would be wasting my time. As Mom taught me, when one lays down
    > with
    > hogs, he comes up smelling like sh*t. The air in this thread is foul at
    > the
    > moment.


    Don't bother, you won't have an audience.

    >>As if your ten minute video would 'prove' anything. Just grandstanding
    >>in
    >>front of your admirers??
    >>
    >>Temperature rise in the motor is not something you can measure with a
    >>thermocouple attached on the outside, or even on the winding. It's
    >>internal
    >>to the slot where the heat has the hardest time being conducted away from
    >>the source.

    >
    > Really? So you think that air is a better thermal conductor than iron,
    > eh?
    > Fascinating.


    It is in this case, since the MOVING air removes the heat.
    You obviously ignored (or don't understand) daestrom's point.

    >
    >>Large motors often have temperature detectors embedded in the
    >>winding during manufacture. Motors that are 'internally protected' often
    >>have the protective device embedded as well. You going to take your motor
    >>and unwind it to put a detector in the proper place? Better not, you
    >>probably wouldn't know how to re-wind it again.

    >
    > But we're not talking about large motors are we? The notion of a thermal
    > protection thermostat being embedded in the tiny slots of a furnace fan
    > blower
    > is hilarious. The "proper place" for the thermal sensor is strapped to
    > the
    > outside of the windings' end turns. Or to the end bell.


    Obviously you are wrong again.

    >
    >>A mild case of overheating internally won't show up as a failure in an
    >>hour
    >>or two, or even a day. But it will shorten the life of the insulation in
    >>the slots and cause failure.

    >
    > Crawfishing. Just what I expected. From this I take it that you're not
    > willing to put your money where your mouth is. Again, what I expected.
    >
    > The original poster can, of course, select whichever advice he desires.
    > Mine,
    > based on experience from someone with a long track record or hypothetical
    > nonsense from an anonymous poster who hides behind a nym and has claimed
    > in
    > the past to be everything from a submarine driver to a nuclear reactor
    > operator. <chuckle>.


    I've always read Daestrom's posts carefully, and have never found any
    substantial error.
    I rarely read your posts, you have an ego problem.
    Daestrom is correct.
    bw, Sep 30, 2008
    #13
  14. Dave

    Vaughn Simon Guest

    <clare at snyder dot ontario dot canada> wrote in message
    news:eek:...
    > The dry air is the OUTSIDE air. The warm damp air escaping is what
    > makes the condensation in between the windows. Seal your INSIDE
    > windows, and allow a small amount of infiltration on your storm
    > window.

    That makes sense...
    > Storm windows in years past had an adjustable "vent" at the bottom to
    > prevent condensation between the panes. **


    I live in south Florida, but was raised in Detroit. You are tickling some
    really old brain cells here... We had the wooden storm windows back then, and I
    don't remember fogging being a big problem. And yes, I think I do remember a
    little sheet metal gizmo in the bottom frame member. Of course, those windows
    weren't sealed in any effective way and provided little insulation effect. I
    think that their main function was to reduce drafts.

    Swapping the storm windows with the screens (that is also when we washed our
    windows) was a rite of season passage that I had long-forgotten. It was a
    process that took most of a weekend and was sometimes delayed too long.

    Vaughn
    Vaughn Simon, Sep 30, 2008
    #14
  15. Neon John <> wrote:
    > On Sat, 27 Sep 2008 08:50:03 -0400, "daestrom"
    > <daestrom@NO_SPAM_HEREtwcny.rr.com> wrote:
    >
    > I started to write a fact-based rebuttal to this garbage but then I realized
    > that I would be wasting my time. As Mom taught me, when one lays down with
    > hogs, he comes up smelling like sh*t. The air in this thread is foul at the
    > moment.
    >
    >>As if your ten minute video would 'prove' anything. Just grandstanding in
    >>front of your admirers??
    >>
    >>Temperature rise in the motor is not something you can measure with a
    >>thermocouple attached on the outside, or even on the winding. It's internal
    >>to the slot where the heat has the hardest time being conducted away from
    >>the source.

    >
    > Really? So you think that air is a better thermal conductor than iron, eh?
    > Fascinating.
    >
    > ...
    >
    >>Large motors often have temperature detectors embedded in the
    >>winding during manufacture. Motors that are 'internally protected' often
    >>have the protective device embedded as well. You going to take your motor
    >>and unwind it to put a detector in the proper place? Better not, you
    >>probably wouldn't know how to re-wind it again.

    >
    > But we're not talking about large motors are we? The notion of a thermal
    > protection thermostat being embedded in the tiny slots of a furnace fan blower
    > is hilarious. The "proper place" for the thermal sensor is strapped to the
    > outside of the windings' end turns. Or to the end bell.


    It's really not.

    plenty of small blower type motors have a thermal protector wedged into
    the slots for the windings.

    tear some motors apart and take a look. The resettable ones are usually
    rectangular cross section metal tubes wrapped in a plastic or paper
    sleeve, with leads coming out one side.
    Cydrome Leader, Sep 30, 2008
    #15
  16. Dave

    Dave Guest

    Re: Resolution of the motor BS (was Re: multi-speed furnace blower motor)

    "Neon John" <> wrote in message
    news:...
    > in the process taking "8X10 Color Glossy Photographs" that would
    > have made Arlo Guthrie proud.


    But, most importantly, did you then put the "circles and arrows on each one
    explaining what each one was"?
    Dave, Oct 1, 2008
    #16
  17. Dave

    Guest

    Re: Resolution of the motor BS (was Re: multi-speed furnace blower motor)

    On Wed, 01 Oct 2008 15:00:53 GMT, "Dave" <> wrote:

    >"Neon John" <> wrote in message
    >news:...
    >> in the process taking "8X10 Color Glossy Photographs" that would
    >> have made Arlo Guthrie proud.

    >
    >But, most importantly, did you then put the "circles and arrows on each one
    >explaining what each one was"?


    Had you followed the link, you would know that he used color-coded
    letters and arrows to create an explanation even the engineers could
    understand.

    John
    , Oct 1, 2008
    #17
  18. Dave

    Dave Guest

    Re: Resolution of the motor BS (was Re: multi-speed furnace blower motor)

    <> wrote in message
    news:...
    >>
    >>But, most importantly, did you then put the "circles and arrows on each
    >>one
    >>explaining what each one was"?

    >
    > Had you followed the link, you would know that he used color-coded
    > letters and arrows to create an explanation even the engineers could
    > understand.
    >

    LOL. I think you missed the point...
    Dave, Oct 1, 2008
    #18
  19. Dave

    You Guest

    Re: Resolution of the motor BS (was Re: multi-speed furnace blower motor)

    In article <FgMEk.171$DK3.110@edtnps82>, "Dave" <>
    wrote:

    > "Neon John" <> wrote in message
    > news:...
    > > in the process taking "8X10 Color Glossy Photographs" that would
    > > have made Arlo Guthrie proud.

    >
    > But, most importantly, did you then put the "circles and arrows on each one
    > explaining what each one was"?


    Not just "Circles and Arrows", but you also need the "Paragraph on the
    Back, Explaining what each Photograph was, and what the Circles and
    Arrows showed".......
    You, Oct 1, 2008
    #19
  20. Dave

    Steve Ackman Guest

    Re: Resolution of the motor BS (was Re: multi-speed furnace blowermotor)

    ["Followup-To:" header set to alt.energy.homepower.]
    In <>, on Wed, 01 Oct 2008
    03:57:03 -0400, Neon John, wrote:
    >
    > http://www.johndearmond.com/2008/10/01/dissection-of-a-furnace-fan-motor/


    $ wget http://www.johndearmond.com/2008/10/01/dissection-of-a-furnace-fan-motor/
    --2008-10-01 16:59:40--
    http://www.johndearmond.com/2008/10/01/dissection-of-a-furnace-fan-motor/
    Resolving www.johndearmond.com... 208.113.199.178
    Connecting to www.johndearmond.com|208.113.199.178|:80... failed: Connection refused.


    --
    ☯☯
    Steve Ackman, Oct 1, 2008
    #20
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