Steady low speed fan control to DIY or buy?

Discussion in 'General Electronics Chat' started by SolarMike, Dec 11, 2012.

  1. SolarMike

    Thread Starter New Member

    Oct 12, 2010
    7
    0
    Hi folks,

    I have a couple of air doors to generate wind over a thermal collector test, but the speed controls that came with them are low rent and at the low speeds I need they seem to hunt around speed wise.

    What is a good strategy to get steady slow variable speed control?
    We mostly do NOT need the higher speeds.

    The control on them is from KB Electronics (HK) Ltd.
    Model KBWC-16
    6.0A FLA
    14.5A LRA
    120VAC

    Motor is 1/5HP draws 3.4A at 120V

    Can I upgrade the KB?
    Is there a higher quality fan dimmer to buy - that is any better?
    Can I build something?


    Thanks,

    Mike
     
  2. Biff383

    Member

    Jun 6, 2012
    49
    19
    There is a trim pot on the back of it (or front?), for speed adjustment. You could try that first.
     
  3. SolarMike

    Thread Starter New Member

    Oct 12, 2010
    7
    0
    Hi,

    Thanks for the reply.

    The speed pot and the low speed trim pot are on the front.

    When I turn the speed down it is uneven - it hunts around. So I need a product or design that is steady.

    SM
     
  4. Biff383

    Member

    Jun 6, 2012
    49
    19
    KB doesn't recomend that controler for low load apps. If you go to something a little higher end it should have a pot named CL. You would adjust that to correct your speed problem.
    You could try putting a load before the fan (resistor, light...) and see if that helps.
     
  5. SolarMike

    Thread Starter New Member

    Oct 12, 2010
    7
    0
    Biffster,

    I am sure Berner (the air door manufacturer) and KB would not have expected a customer to want less air not more. But that is how it is.

    I will try a lamp to see what that does, try to jack the amperage up nearer the FLA. I have some big halogens. (5A x 120V = 600 Watts - I will need a lot). I do have some big resistors too - coils on ceramic tubes with sliding contacts. Be a shame to have to make a toaster oven just to slow the fans down enough.

    You said:
    "If you go to something a little higher end it should have a pot named CL"

    I don't understand "named CL" can you recommend a manufacturer?

    I haven't been able to find anything higher end except for big variacs and stuff, which seemed excessive. The local motor shop has the KBs, but nothing else.

    I probably don't know the right way to search for this. Rheostat doesn't do it. Fan dimmer, motor control, etc. nothing like what I need. Haven't hit on anything that seems right. Would like to get something under $50. (4 times what the KB costs).

    I wish I knew what better looks like. The KB is really lightweight.

    Thanks!
     
  6. Biff383

    Member

    Jun 6, 2012
    49
    19
    You should be able to get away with 100 watts of load.
     
  7. Biff383

    Member

    Jun 6, 2012
    49
    19
    The CL thing is on DC drives, sorry I just woke up a bit ago and happened to be looking at a KB drive when I saw your post.
     
  8. gerty

    AAC Fanatic!

    Aug 30, 2007
    1,153
    304
    CL = Current Limit
     
  9. SolarMike

    Thread Starter New Member

    Oct 12, 2010
    7
    0
    Hi, I am bumping this because I had hoped to learn about circuits that can be used to slow an AC motor. Like the KB fan "dimmer" I have, only better.

    Thanks,

    SM
     
  10. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
    1,305
    Exactly what type of "AC motor" is it? Do you have a photo of the motor?

    Just about anything can be slowed down if you are prepared to build a special circuit.
     
  11. SolarMike

    Thread Starter New Member

    Oct 12, 2010
    7
    0
    I am willing to build a circuit, no problem. But, if nothing else I would like to know how the KB or similar controls work. Oddly, I can't come up with much. My searches just aren't hitting on much.

    The application is an "air door" from Berner. The motor is listed in their literature as 1/5HP. It is spinning a long centrifugal blower. I call it a squirrel cage blower." Not sure if that is proper. It is not especially high speed, you might guess a 2 pole. I am in the US therefore 60Hz.

    I assume, since they sell these as their main business, that the motor is well suited, including that it can have its speed adjusted by the simple means of this cheap KB controller. You electron jockeys may be able to tell a lot from this, but I cannot.

    In answer to the question, "what kind of motor is it," what else do you need to know and how would I tell by looking at it?

    Thanks for working with me on this,

    SM
     
  12. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
    1,305
    Mainly if it has brushes or not. If so, it is likely a universal motor as used in some blower fans and things like vacuum cleaners etc. Large blower fans usually have cast metal frame induction motors that run a fixed speed (like a large drill press or air compressor motor).

    The brushed "universal" type of motor can be controlled with a cheap "phase angle controller" or "drill speed controller" "electric motor variable speed controller" etc. I think Harbour Freight store have one for about $40 that will do power tools and will do a small motor like your 1/5hp fan motor.

    Lukily your load is a nice one, fans are a very constant load and should be easy enough to control with a cheap open-loop controller like the Harbour Freight one.
     
  13. SolarMike

    Thread Starter New Member

    Oct 12, 2010
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    0
    I showed the controller to someone would know and he said its a phase angle controller. Now I know what to call it maybe I can find some circuits.

    I don't think this is a brush motor. They have a particular sound. It is probably an induction motor. I didn't have a chance today to look at it.

    I got another possibly good non electrical solution - block a lot of the intake until I lower the flow to where I need it to be. At least I can try that out with a roll of tape.
     
  14. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    If the controller is a phase angle controller you can use the Harbour Freight controller or any other cheap motor speed controller.

    Re the blocking off of the airflow, that may not work with your present controller as it is already unstable "hunting around" you said so it may not respond well to adding a load. However I suppose it is low effort and low risk so maybe it's worth trying before buying another controller. :)
     
  15. SolarMike

    Thread Starter New Member

    Oct 12, 2010
    7
    0
    THE_RB, Thanks!

    "Re the blocking off of the airflow, that may not work with your present controller as it is already unstable "hunting around" you said so it may not respond well to adding a load."

    Actually blocking the intake or outlet reduces the load. Like when you stop off your vacuum -the motor speeds up, not because it has to work harder, but because it is no longer moving air (Except in a circle) and it can rev higher. You can prove this by putting an amp meter in line and watching the current drop when you stop it up.

    But, really I just want to let it run faster and starve it down to the CFM I need. Hopefully, with an unadulterated phase angle and more rotational inertia it will be steadier. I found a big sheet of corrugated plastic to use inside the intake grate. Next year though. Not right away.
     
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