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Jeff Wisnia

wrote:

On Jan 29, 3:45 pm, Jeff Wisnia wrote:

Gerry Atrick wrote:

On Mon, 29 Jan 2007 00:34:31 -0600, "Steve" wrote:

Small motors typically have bushings instead of bearings. Bushings wear out
sooner. The axle is jigging around inside the bushing until the structure
warms up a bit -- could be the axle swelling from heat, or dirty lubricant
softening up, or something else a more knowledgeable person will point out
later.

I fix a lot of these for clients. Clean the gray gunk off the fan blades
with a can of compressed air. That usually solves the problem. If not,
replace the fan. They're less than 10 bucks, unless you go for the gaudy
ones with LEDs. Clean out all the rest of the dust in

If you want, you can try some light oil, but don't use much. You definitely
don't want oil inside your PC. In fact, don't use oil unless the fan blows
OUT of the case. I've always just replaced the fan, because I'd have to
charge more for half-measures.

I won't presume to advise you about your heater. Your barn might burn down,
and then I'd be sad.

I hate to tell you this, but because you did NOT advise me about the
barn heater fan, the heater burst into flames and burned the whole
barn down, killing all the animals and several workers. It was
horrible. It's your fault for not giving me help. You will be
hearing from my lawyer, who is also my wife, and she sleeps with the
judge a few times every week, so you dont have a chance to win the
case.

Well, OK, I'm just giving you some **** and the latest Jerry Springer
episode....

Seriously, I just oiled that fan motor in the heater. It dont seem
like it's worn too badly, but the oil quieted it down. There was a
little fire though, (almost). I dripped some oil on the heater coil
and that sure smoked for a few seconds. It works quiet now.

This heater is strange in design. The motor looks like one of those
old record player motors but the coil windings are thick. Probably a
#12 enamelled wire. The heater coils are connected in series with
that motor. Thats an odd design. I cant understand the point to
that, other than if the motor burns out the coils will not heat.
Otherwise it makes little sense and that is why that wire is so thick.
Thats a lot of amperage to go thru that small motor.Might be because a smaller number of turns of heavier wire is a bit less

costly to manufacture? And, a motor wound with heavier wire has a
slightly lower chance of the wire breaking from vibration at a termination.

Ampere-turns is what sets what the motor does, and you can get the same
amount of them with lots of turns and lower current or fewer turns and
higher current.

I confess I've never run into a small heater wired like that, but now
that I think about it the setup sounds like it would provide a bit of
positive feedback of the element temperature, which sounds sort of bass
ackwards to me.

i.e. when the element is cold, the curent through the motor is greatest,
causing the motor to run a bit on the fast side, cooling the element
more, and conversely when the element was hot and the current draw was
less, the motor might run a bit slower, leading to less cooling and an
even higher element temperature.

Hopefully someone smarter than me will give us a good reason for that
setup, beyond the possibly lower manufacturing cost.

Jeff

--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.8*10^12 furlongs per fortnight.

Depending on the type of motor, it could have its speed determined not
by the current, but by the frequency.

Dave

Agreed, but what does that info add to this thread Dave?

Isn't it rather unlikely that the OP will be running that heater on
anything other than 60 (or maybe 50 ) Hz power?

If "Gerry Atrick" is also the OP, then by describing the motor as a
"phonograph motor" style, he's probably talking about a shaded pole
induction motor, which was the most common motor type used in record
players once they gave up on the crank wound spring motors.

There were a few high end record "turntables" which contained
hysteriesis synchronous motors, which would have been the type you
brought up, but it's highly unlikely anyone would waste the money on
that type of motor to drive a fan, 'eh?

Jeff

Jeff

--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.8*10^12 furlongs per fortnight.