Is jamming a DC fan harmful?

  • Thread starter Thread starter Bucky
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Bucky

I was wondering if it is harmful to prevent a DC fan from spinning by
jamming a piece of paper in it. This is a small (30mm diameter) plastic
fan, of the cheapest quality. Will it cause the motor to overheat or
cause any safety issues? Or is it perfectly harmless?

I have an external hard drive enclosure that has a small fan (30mm)
that is chattering loudly. I cannot disconnect the fan's wires due to
tight space, and I don't want to permanently snip the wires either (I
still have to determine how hot my drive gets with no fan).
 
Bucky said:
I was wondering if it is harmful to prevent a DC fan from spinning by
jamming a piece of paper in it. This is a small (30mm diameter) plastic
fan, of the cheapest quality. Will it cause the motor to overheat or
cause any safety issues? Or is it perfectly harmless?
Click to expand...

I just tried this out. After 5 minutes, I felt the fan, and it was
really hot. So I'm guessing that the jamming the fan does indeed cause
the fan to overheat.
 
Bucky said:
I just tried this out. After 5 minutes, I felt the fan, and it was
really hot. So I'm guessing that the jamming the fan does indeed cause
the fan to overheat.
Click to expand...

If you read some of the reviews on Quiet PC Review you will see that
they measure the power used by a fan under normal use and when jammed.
When they are jammed most of them use almost double the power. So the
fan will get hot very quickly, especially without the fan moving air to
cool the motor.
 
A motor is a generator too, when you apply voltage/current
to a motor that isn't turning, it acts very much like a dead
short since it is just a longer bit of wire wound in the
motor. But when it begins to rotate there is a magnetic
field created which generates a reverse voltage in the
wiring, so the motor running at rated speed has 12 volts
going one way and maybe 10 volts going against the applied
current, so the motor is running on a two volt difference in
EMF (voltage). The ohms law will then have acted to limit
the current in the motor.


message
| Bucky wrote:
| > Bucky wrote:
| >
| >>I was wondering if it is harmful to prevent a DC fan
from spinning by
| >>jamming a piece of paper in it. This is a small (30mm
diameter) plastic
| >>fan, of the cheapest quality. Will it cause the motor to
overheat or
| >>cause any safety issues? Or is it perfectly harmless?
| >
| >
| > I just tried this out. After 5 minutes, I felt the fan,
and it was
| > really hot. So I'm guessing that the jamming the fan
does indeed cause
| > the fan to overheat.
| >
|
| If you read some of the reviews on Quiet PC Review you
will see that
| they measure the power used by a fan under normal use and
when jammed.
| When they are jammed most of them use almost double the
power. So the
| fan will get hot very quickly, especially without the fan
moving air to
| cool the motor.
 
Jim said:
when you apply voltage/current
to a motor that isn't turning, it acts very much like a dead
short since it is just a longer bit of wire wound in the
motor
Click to expand...

Thanks, great explanation!
 
Mike said:
Replace the fan..
Click to expand...

Yeah, I guess that's what I'll have to do. It's just such a pain
because of the tight quarters. Plus the fact that this enclosure is
brand new, so it's not like the fan is worn down, it's just that cheap.
I don't think exchanging will do any good because the next one will
have just as cheap of a fan.
 
you should get it replaced(called warranty), if it's new. keep replacing
them, if needed. the fan is there for cooling. allowing for heat to build up
will destroy device in enclosure. which is cheaper? can you afford to loose
the device and data?
 
Thanks, something they teach in aircraft mechanics school.


| Jim Macklin wrote:
| > when you apply voltage/current
| > to a motor that isn't turning, it acts very much like a
dead
| > short since it is just a longer bit of wire wound in the
| > motor
|
| Thanks, great explanation!
|
 
You could end up with overheating, a short circuit, a ruined drive, or all
of the above if you jam the fan so it doesn't rotate. Your external hard
drive requires cooling (otherwise there would be no fan), so you need to
replace the fan rather than just disable it. Is the HD still under warranty?
If so, get it replaced. If not, get it replaced anyway - or get it's cooling
fan fixed.

On the other hand, if your HD is an internal one that has been mounted into
an external fixture that has a fan, then perhaps it doesn't need the fan.
Does the HD get too hot to touch?

By the way, I have 3 desktop computers, all with internal HDs. None of them
ever get too hot to touch (warm, but not hot). They are not tightly packed
in their computer cases, so the only cooling they require is from regular
case fans.
 
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