Hello

I need to reduce the speed a fan rotates but I don't know what sort of
motor powers it. I assume it it brushless and therefore possibly an
induction motor because it is part of a refrigeration compressor unit
and presumably designed for long maintanance free use.

Are there any clues to look for when trying to identify the motor type
or is it possible to use a "fix-all" device that will slow all types of
motor

my thanks in advance

Nick

In article ,
Nick Brooks wrote:

I need to reduce the speed a fan rotates but I don't know what
sort of motor powers it. I assume it it brushless and therefore
possibly an induction motor because it is part of a
refrigeration compressor unit and presumably designed for long
maintanance free use.

Are there any clues to look for when trying to identify the motor
type or is it possible to use a "fix-all" device that will slow
all types of motor

If there are no brushes then it is an AC motor and
if there is no big capacitor it is a shaded pole
induction motor. This is the normal type of motor
used for fans.

If it is a proper fan motor (quite likely) then the
rotor resistance will be higher than normal, which
allows speed control by reducing the supply volts.

Simple speed controllers for fans are available, either
all-electronic or by tap-switching an auto transformer.
The better controllers run the fan up on full voltage
then drop back to the set voltage.

See Farnell's catalogue at http://www.farnell.com in the
Heating, Ventilation and Air Conditioning section.

--
Tony Williams.

Most small fans can be slowed by fitting a series resistance.
Capacitors are my favoured method, but if using a capacitor do make
sure the motor runs slower with your chosen cap, if it runs faster or
hotter, switch off. (Its possible to pick a C value that resonates with
the motor L). Other options are an inductor or a high power light bulb
in series with the motor.

Its not impossible to overheat a fan like this, but it doesnt normally
happen.

NT

"Nick Brooks" wrote in message
...
Hello

I need to reduce the speed a fan rotates but I don't know what sort of
motor powers it. I assume it it brushless and therefore possibly an
induction motor because it is part of a refrigeration compressor unit
and presumably designed for long maintanance free use.

Are there any clues to look for when trying to identify the motor type
or is it possible to use a "fix-all" device that will slow all types of
motor

my thanks in advance

Nick


Is it a mains voltage motor, or is there a transformer near by? Could it be
supplied through another piece of equipment in an appliance it is fitted to?
The refrigeration unit may not take to kindly to having the fan being slowed
down and reducing the air flow over the compressor unit, so you'll have to
be aware of this. The need for a fan assisted air cooling system means the
compressor runs hot enough to need this type of system.

Is the need to slow it down because it's noisy? It may just need new
suppressor pads on its fixing points to stop it rattling against things if
it is.

A mains voltage motor can be set to half speed with the use of simple diode
in line with one supply conductor. The diode needs to able to withstand the
repetitive reverse voltage of course, but it is the simplest way to make a
motor run at half speed.

BigWallop wrote:
"Nick Brooks" wrote in message
...

Hello

I need to reduce the speed a fan rotates but I don't know what sort of
motor powers it. I assume it it brushless and therefore possibly an
induction motor because it is part of a refrigeration compressor unit
and presumably designed for long maintanance free use.

Are there any clues to look for when trying to identify the motor type
or is it possible to use a "fix-all" device that will slow all types of
motor

my thanks in advance

Nick



Is it a mains voltage motor, or is there a transformer near by? Could it be
supplied through another piece of equipment in an appliance it is fitted to?
The refrigeration unit may not take to kindly to having the fan being slowed
down and reducing the air flow over the compressor unit, so you'll have to
be aware of this. The need for a fan assisted air cooling system means the
compressor runs hot enough to need this type of system.

Is the need to slow it down because it's noisy? It may just need new
suppressor pads on its fixing points to stop it rattling against things if
it is.

A mains voltage motor can be set to half speed with the use of simple diode
in line with one supply conductor. The diode needs to able to withstand the
repetitive reverse voltage of course, but it is the simplest way to make a
motor run at half speed.




Yes, it's mains voltage and I've bought a Fan speed controller (off ebay).

The fan/compressor/evaporator unit is new and does need to be slowed
down because it's too noisy. I've checked with my friendly
refrigeration engineer who said that the compressor doesn't need ANY
airflow as it is cooled by returning refrigerant.

Thje evaporator will be less effective with slower fan speeds but the
air speed is so great at the moment that the air coming off it is
indistinguishable from ambient. I'll monitor the duty cycle to make
sure I don't slow the fan too much.

Thanks for all replies

Nick