×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Motor randomly reversing

Motor randomly reversing

Motor randomly reversing

(OP)
Hi Folks,

I have a pool heat pump where the fan motor is acting erratically. The fan will engage either clockwise or counterclockwise on different attempts, seemingly at random. Occasionally it will also hum and not turn at all, unless assisted by a screwdriver, in which case it will run in the direction assisted. The motor is supposed to always run CW.

Any ideas what the problem might be?

Thanks!

RE: Motor randomly reversing

If there is a capacitor involved it has failed.

If there is a centrifugal start switch involved it could have failed. That is the standard failure mode of single phase induction motors - the centrifugal start switch.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Motor randomly reversing

It could be a broken shading coil but Keith's suggestion is several thousand time more likely.
I have seen many failed capacitors over the years as well as many failed centrifugal switches and only one broke shading coil.
And further, the broken coil was on a contactor and not a motor and shaded pole motors typically have two shading coils and one should be enough to start a fan in the proper direction, albeit slower than normal.
Follow Keith's advice.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

RE: Motor randomly reversing

(OP)
Thanks guys.

The motor is a CF-9622: https://www.alltemp.ca/product/cf-9622/

Can we tell if that has a centrifugal switch?

I could easily test the capacitor - I think - just by measuring the resistance change, and by verifying the capacitance with a DMM?

Thanks!

RE: Motor randomly reversing

It is easier to just replace capacitors. They get leaky (electrically) and can give you all kinds of odd readings.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

RE: Motor randomly reversing


Permanent Split Capacitor, no centrifugal switch.
With a blown capacitor and a little back draft on the fan, this will start in reverse.
The textbook resistance of a perfect capacitor is infinite, and the resistance of a blown capacitor may be infinite.
But,
When you try to measure the resistance of capacitor with an Ohmmeter, the ohmmeter measuring current charges the capacitor.
The Ohm reading depends on the current in the measuring circuit.
As the capacitor charges, the current drops and the indication goes upscale towards a very high resistance.
Once the capacitor becomes charged, the reading stabilizes at a high resistance value.
If you then reverse the Ohmmeter leads and test again, the meter will initially pin at zero Ohms as the stared charge is dissipated in the ohmmeter circuit. The reading will then drift upscale again.
If you have an analog meter, the moving needle shows this much better than the rolling digits of a digital meter.
If the DMM has a capacitor check function that may work, but I have been disappointed more than once by DMMs that did not have the capacity to check large motor circuit capacitors.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

RE: Motor randomly reversing

Dear Mr. enigmapaul
1. Capacitor failure is the first (very likely) suspect. Look out for leakage or tank being bloated; but some times without any external physical deformation, (dry out=open circuit) internally.
2. The replacement capacitor may be from any manufacturer, physical shape/size that suits the bracket, metallic or plastic tank.
3. It is important that the replacement capacitor shall be of equal or slightly higher voltage (Vac) and capacitance in (mF) ratings. However, it is (not critical) to be of the [exact value].
4. You may get it from electrical stores or AC workshops. Motor rewinding workshops do not stock them.
Che Kuan Yau (Singapore)

RE: Motor randomly reversing

You need a motor running capacitor, not a motor starting capacitor.
A motor starting capacitor is not suitable for use on a Permanent Split Capacitor motor.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

RE: Motor randomly reversing

As a complete aside, brought a chuckle remembering a similar issue with an oven damper system.

The OEM's recommendation was to monitor the damper position feedback against the commanded direction (e.g. open/close) through the SLC500. If going the wrong direction or not going at all, simply interrupt, pause a second or two, then re-engage the movement command. Of course, they didn't provide any code to back up their recommendation, and too expensive to bring their resources in from across the pond, so another opportunity to excel at the rubber-meets-the-road, gitter-dun-or-else plant level.

Well, it worked quite well, but not a solution I would expect from the OEM of the system...

RE: Motor randomly reversing

The solution that gets you off the phone with them is a good solution from their viewpoint…


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

RE: Motor randomly reversing

(OP)
Checking the capacitor in question, yields no reading on a DMM capacitor meter. Also yields infinite resistance instantly and not changing over time, in both directions.

RE: Motor randomly reversing

Sounds completely open failed or shorted failed you don't specify the resistance.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Motor randomly reversing

I'm usually overlooking stuff like this. grin

Quote:

Also yields infinite resistance instantly

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

RE: Motor randomly reversing

Since the motor hums but runs once given a push, isn't it a starting cap issue?

Muthu
www.edison.co.in

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Resources

Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close