speed control question

[wolfiehogan]

hi guys
have a question on the speed control of a fan. was told to instal a speed control for a fan. the speed control was varying the voltage off the fan from 230, 110, 80, but i cant understand how a 230 fan would not burn out running on lower voltages and when measuring the amps at different speeds actually went down and i taught they would go up. can some body fill me on how this works please

 

[Deleted member 26818]

It probably uses a rheostat, to increase resistance and slow it down.
Or perhaps a solid state version.

 

[telectrix]

amps will go down at lower voltages as the motor is running slower and does not draw as much current. and you have to be careful with speed controllers. if you go too low, the motor can stall and then burn out. the controllers i have fitted have a preset min. control ( a small pot. on the pcb ) to adjust so the operator can't damage the fan

 

[wolfiehogan]

can you explain more how this work please

 

[wolfiehogan]

is there a way to vary the frequency instead off the voltage without incurring large costs

 

[telectrix]

i know iof you fit them right, turn the knob and the fan goes faster or slower. the intricacies of the magic insides, i leave to the silicon geeks.

 

[DurhamSparky]

normally speed of fans is controlled by VSD on the frequency as already mentioned!! .... its "white mans magic"

 

[Sparks-R-Us]

Motors must be well loaded for optimum speed control, so choose one that is just big enough for the application. The
motor load must be at least 75% of the nominal power of the motor at maximum speed. Choose a speed controller
with a maximum current that is just larger than the nominal motor running current, i.e. if motor rating is 2.95 amps,
select a controller with a maximum current of 3 amps. Several motors can be connected to one speed controllers
long as the controller’s maximum current is not exceeded. Although rare, some motors can have a higher current
consumption, when run at lower voltages, than the motor’s nominal current at design voltage. The highest current
should be used when selecting the speed controller. These controllers are not suitable for use with some back up
generator systems.

It is recommended that a fused mains isolator is installed upstream of the speed controller. The fuses should be of the
slow blow type with a current rating that is the same as the speed controller’s internal fast blow fuse.