Rebuilt HVAC fan motor spins backwards, rebulider says that's not possible

[valvashon]

Greetings- this is my first post. Hoping that this forum is more helpful than some others.

Short history- I've been interested in electronics since I was little, went to school for TV and engineering, landed a TV station job and moved up to maintenance engineer and satellite truck operator. About two years ago they handed me the building maintenance duties as well.

There was an incredible number of things unfinished or unstarted by our previous building maintenance engineer. If it wasn't easy it didn't get done. Finding new Broan dual shaft vent fan motors was impossible, so the doors to the transformer rooms sat propped open. I finally found a motor rebuilding shop that would do it, so over the past year I have sent them the two dual shaft motors, as well as four other HVAC fan motors (from inside of the VAV units in the ceiling).

Trouble is, their work has been less than stellar. The two dual shaft motors had to go back under warranty for bearing failure within three months (they are back now and doing fire), the first VAV motor I sent in came back reversed in it's cage so it wouldn't mount up properly (I turned that one around myself), the second one I sent in came back reversed in it's cage (I sent that one back), the third one came back fine (we had a spare so the rebuilt one is now the spare) and the fourth one came back and spun backwards when I installed it!

The HVAC VAV motors I have been sending in are three speed (usually set it and forget it with a switch on the side of the unit) single phase units on 277 volts. Small, maybe 1/2 HP or so with rotation speeds between 500 and 1100 RPM or so. All with motor run cap between 5 and 12.5 uF. I'm kind of stuck with this re-builder as I can't find another place that wants to work on small motors. Rebuilding is cheaper plus finding the motor in the correct mounting cage for these 20 year old VAV units is next to impossible.

With the latest one, I was under the impression that it was just bad bearings. When the shop got the motor they said a winding was bad as well. I, of course, was not able to observe the rotation direction of the unit prior to sending it in. When I got it back, I put the squirrel cage on the shaft and the assembly in the mounting housing. Based on the marks on the shaft and the way the fan sits in the housing, it can go on only one direction. These things sit offset in the housing a bit, with the air flow coming out the wider part of the opening. Mounted it in the VAV, hooked it up (including the correct capacitor), set it to the medium speed and powered up. First thing I noticed was that the speed didn't seem to change much if at all with the Hi-Med-Lo switch on the VAV, plus when I went to Hi (I think) there was kind of an odd thump or pop coming from somewhere. Set it to medium speed again and noticed the lack of airflow out of the vents. Put my hand directly on the output and then noticed the lack of air. Shut things down and noticed the backwards rotation as it slowed to a stop (as compared to the "rotation" speed arrow). Spun it the correct direction; powered up and it reversed and spun the wrong direction again. Took it down and hooked it up in the shop and found it still rotating backwards.

Re-builder insisted that this can't happen and that their shop strapped the windings correctly, but offered to have a second look, so I sent it back. My question is this- is it possible to wire it up so it starts backwards? They insist that can't be done, but something determines the rotation.

Also, can you recommend a good small motor re-builder?

Thanks-

Val

 

[waross]

If this is a shaded pole motor, the stator core may have been reversed in respect to the end bells.
That is the front end bell was installed on the back and the backend bell was installed on the front.
The way to reverse a shaded pole motor is to dismantle it and to reassemble it with the stator core reversed.
If the motor has a wound starting winding then the connections to the starting winding are reversed.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[valvashon]

Thanks for the response. It's not the shaded pole type so hopefully they will find the starting winding reversed.

Their work is so iffy I had to put in a 277 volt outlet (L7-20) in the maintenance shop so I can do a test hook up on everything before I install it.

Val

 

[Compositepro]

If the motor is being rewound, there is a 50/50 chance on which direction it will rotate, unless a check is done to make sure it will rotate in the correct direction.

 

[edison123]

The insistence that it is not possible to reverse a single phase motor rotation direction and the fact they did not check the rotation direction before sending it back to you confirms rewinder is incompetent. As others have said, in this case, the starting winding has been reversed and it has to be corrected. It is a one-hour job for a good rewinder.

As a rewinder myself, we do not undertake small motors repair any more since the repair vs replacement cost is no more debatable.

I do applaud you for making the effort to do it the 'old fashioned way' as well as for posting here a well explained problem. Very few maintenance engineers do that now a days.



Muthu

http://www.edison.co.in

 

[itsmoked]

Muthu: I think not supporting small motors in rewinding is a huge mistake. The logic that 'why would one do that when new small motors cost so little' makes complete sense. That is, until the small motor is something non-replaceable, impossible to find, and badly needed.

Most the motors I consider replacing are completely unfindable. They have a one foot shaft, or bizarre mounting points, or weird power like 3Φ 120V, or some other crazy oddity that comes down to nothing to do with the motor power/HP and everything to with the stuff that surrounds the motor.

We just had a blower motor wedged into a rail car that was "un-replaceable". It cost about $9k to tear the car apart and completely replace everything surrounding it to work in a sort-of-similar newer motor. We'd have paid plenty to rewind that 1-1/2 motor but shops all said "1-1/2 too small". Someone could open a national small weird motor rewinding shop and make bank I bet.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[edison123]

Keith - We do rebuild 'special' (aka weird) motors like that as long as the client is willing to foot the bill. We even 'reverse engineered' a few motors from ground up ("greenfield projects") for those few clients who didn't give a s**t about the cost and just wanted 1-1 replacement spares. And our winders tremendously enjoyed doing such whacko repairs/rebuilds.

But mostly, I found it irksome to 'justify' the cost of repair/rebuild with some know nothing bean-counters repeatedly and just gave up.

Muthu

http://www.edison.co.in

 

[itsmoked]

Ah. That is good to hear. I'm relieved. I was worried that nixing small motor repair meant weird tools, jigs and what-not all got pitched, and hence the ability got pitched as well. Next time I have a weird one I'll look you up.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[edison123]

Keith - This is one of the 12 weird monsters (called Blanchards) which we rewound and refurbished over a period of 4 years. Don't be fooled by the size. It's still a low HP, low speed machine from 50's made by GE (when GE was actually being GE).

The client had scoured the scrap markets around US of A and mopped up all the available ones.

Then two years later, they come to us and ask "guyz, we want more of these but none is left to buy, can you make them for us?"

Yes, we were delighted, why do you ask?


Muthu

http://www.edison.co.in

 

[edison123]

Sorry about the size of the pics. I had no control over it. May be the site admins can resize them?

Muthu

http://www.edison.co.in

 

[itsmoked]

Muthu I see no size issues with the picture.

HAh! Blanchards! I work at a place that has seven of them. The 50HP ones are enormous and I always look at those motors that are about the size of a 55 gallon drum and wonder "what am I going to do when one of those fissile.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[edison123]

Now you know where to send those monsters.

Muthu

http://www.edison.co.in

 

[valvashon]

Update-

Got a notice early this morning that this motor is being shipped and will be here by Friday. Thought that was odd as there was no invoice. Did they really have to do a warranty repair? Yes they did- just got the invoice about the motor- it's marked as "warranty repair". Looks like it could spin backwards!

You bet I'm hooking it up on the test jig on Friday!

Val

 

[valvashon]

This won't be a surprise to anybody here- I received the motor over the weekend and hooked it to my 277 volt outlet- it spins the correct way! Hooray for air movement! It's getting a half hour test at each speed before I install it. I don't want any surprises this time.

Val