Fan speed control

[GENERALCOOL]

Hi friends,
As you know some companies such as SAGINOMIA or JOHNSON CONTROLS or …. Have a products called "Fan speed control" that they decrease velocity of condenser fan while discharge pressure decreases.
I have a question, Do these products for decreasing velocity of fan decreases input voltage of fan or frequency ?

Thanks.

[NH3LVR]

Have not worked on one of these in a long time. The ones I did work on were by Johnson.
They reduced the voltage on two of the 12 motors when the Ambient was low.
They also burned out motors. Because we did not have extreme temps and low loads we removed them.

[Tayters]

Not sure if those makes are special but generally fan speed controllers for small motors use a SCR or triac to let a portion of the AC voltage through.
More of the waveform that is switched on then faster the motor goes.
Same way the household light dimmers work these days. I found these links which explains it better than I can.

https://home.howstuffworks.com/dimmer-switch2.htm

https://m.youtube.com/watch?v=5-wPkFv6eJE

Cheers,
Andy.

[Glide]

Have not worked on one of these in a long time. The ones I did work on were by Johnson.
They reduced the voltage on two of the 12 motors when the Ambient was low.
They also burned out motors. Because we did not have extreme temps and low loads we removed them.

I've heard this before. Why do they burn motors?

[Glide]

Here is a copy/paste from Danfoss / Saginomiya datasheet:


When pressure is declining the controller decreases the output voltage changing the speed of AC/EC fan motor.


For min. pressure the controller can either operates with min. speed or completely cuts off the output voltage, depending on the type of the controller.

Link to a datasheet:

https://assets.danfoss.com/documents/DOC227986440750/DOC227986440750.pdf

[NH3LVR]

Why do they burn motors?
Am not entirely sure. These were Single Phase (The other ten were Three Phase).
There may have been a misapplication from the Factory. Dunham Bush was having a great deal of problems then and Customer Service was virtually non-existent. (This was in 2002)
We had to replace the Speed Controllers and the motors. This was my first time working on large (270HP) Air cooled Chillers and they were definitely built to a price.
It does not seem to me to be a good way to control Motor Speed. But Technology then was not as good as today.

I also had a issue with the Motor Terminals leaking These were Semi-Hermetic Screws. I had a bit of luck talking to an Engineer at their Hartford Division. I was looking for someone with experience to replace the Terminals. He suggested that I use the new repair kits to seal them. That there was such a thing was apparently not known to the Service Manager.

I did feel better when the President of DB called me to apologize for all the problems.

[chemi-cool]

I've heard this before. Why do they burn motors?

Its very common thing on large condensing unit with many fans.
When a single phase motor is lowering its speed by mean of decreasing voltage, its currant absorbing is increasing creating more heat.
The single phase motor fighting to pull air and not having enough power, gets very hot and burn much quicker.

Best way to control speed is by employing a frequency converter controlled by head pressure on all fans.

[GENERALCOOL]

Its very common thing on large condensing unit with many fans.
When a single phase motor is lowering its speed by mean of decreasing voltage, its currant absorbing is increasing creating more heat.
The single phase motor fighting to pull air and not having enough power, gets very hot and burn much quicker.

Best way to control speed is by employing a frequency converter controlled by head pressure on all fans.

Thanks.
Exactly my question was this matter. As you know while we decrease voltage of a motor current increases and finally it will burn.

15525

15526

But you see Danfoss decreases output voltage of fan and as you told best way is to change frequency for controlling speed of fan.

How it will work ????

[chemi-cool]

That will work with small diameter and low air volume fans

[GENERALCOOL]

That will work with small diameter and low air volume fans

Thanks for your reply.

[Desaster]

Hi,

attention to buy an inverter with sine filter if you connect more than 1 fan.
https://library.e.abb.com/public/8c253c2417ed0238c125788f003cca8e/ABB_Technical_guide_No5_RevC.pdf