Fan Motor

[Coolie]

Got called to Tower 42 today to look at one of our clients comms room a/c units. They reported it as blowing out hot air!
When I finaly got to the plant room on the 31st floor I found the following:
System: I.M.I. (Maastair) split. AHU type condenser.
Finding the problem was easy. I stuck my gauges on the system to find the standing preasure to be ok. After turning the power off and back on the system compressor kicked in straight away, as did the fan. Problem is the fan stops running after about 5secs. It's a single phase 6pole direct drive motor. There is still 240v going to the fan after it cuts out. Nothing changes to the fan execpt that it stops running. It has not gone out on it's thermal protection as the motor is cold to the touch (about 20 degrees c). I checked the capacitor and it is o.k.

I have ordered a new motor to replace it, but I would be interested to find out what is causing this to happen.
I think that the thermal cut out inside the fan motor has malfunctioned, causing this to happen.

Oh, the compressor cuts out on HP about 10 secs after the fan stops.

Any Suggestions?

[Coolie]

It's R407c by the way, not that has anything to do with the fan!

[chemi-cool]

Hi Coolie,

Why not take it apart and inspect it.

Ballbearing or sliding bearing failure is the main reason.

Low quality motors is also a good reason.

Chemi

[chillin out]

hi coolie you said you had 240v to it, did you check for a neutral?


ps re your sig.

they might even become your boss

[chemi-cool]

hi coolie you said you had 240v to it, did you check for a neutral?

How can you check 240V if there is no nutral????

Chemi

[chillin out]

people tend to use the earth when testing voltages.
you can also use a volt stick or testing screwdriver.


theres more that one way to skin a cat

[chemi-cool]

people tend to use the earth when testing voltages.
you can also use a volt stick or testing screwdriver.


theres more that one way to skin a cat

I knew you will say that!

Checking the voltage on a one phase system, is between phase (live) and neutral.

If you measure 240V between earth and phase, it shows you that the unit is grounded.

Chemi

[frank]

Just a thought but on IMI the head pressure controller cuts the neutral based on the liquid line temperature. this is a normal way of fan speed control.

To check whether the fan speed control board is at fault you can move the neutral wire from pin 1 to pin 2 to by-pass the control (as you would during commissioning)

Did you do this before you condemned the fan motor?

Be interesting to see how this pans out

[Coolie]

Thanks for the suggestions guys.

I did check the neutral and while the fan was running I measured 240volts between live and neutral. I also measured 60v between live and neutral after the fan had cut out.
There is no seperate fan speed control board, the fan connects directly onto the main pcb. Also it says on the fan scroll housing that it is a single speed fan motor!

[Brian_UK]

.... measured 240volts between live and neutral. I also measured 60v between live and neutral after the fan had cut out....

OK, so where has the other 180 volts gone then ?

What's the model no. of the unit ?

[Coolie]

I have not got that detail on me, I'll post it tomorrow!
What are your initial thoughts?

[Feeze]

Hi Coolie,
I am not familiar with the system however these are my thoughts on the fault tracing:
You say that you do not think that the thermal cut out is opening as the motor is cold to the touch.
Have you confirmed this by measuring for continuity?
Is the thermal cut out (klixon) wired up in series with the power feeding the windings of the motor or does the klixon cut the power to a contactor which may be feeding the motor?
Have you measured the resistance of the motor winding before it cuts out and then also after it cuts out?
Where are you taking your voltage measurements, at the motor terminals or at the source of power feed?
You say that there is still 240v going to the fan after it cuts out, so then when is it that you get a reading of 60 volts?
I suspect that the 60 volts may be a back emf reading from the fact that the fan blades are not perfectly still.
Take all these measurements before condeming the motor.
How long is the period after the fan cuts do you have to wait before it will restart?
Have you tried turning the blades manually- do they turn smoothly or are thy tight?
Have you taken amperage measurements?

Cheers,
Feeze


I

[chillin out]

Suggest you trace the wiring all the way from the fan to supply find the fault, repair it and then fit the new motor youve already ordered and recycle the old one somewhere else.
bobs your uncle job done .

If its the speed controller , a live feed through a h/p switch to the fan gets the job done same day without ordering another part.

[frank]

Which reminds me too, those fan speed controllers always start the fan up on full for the first few seconds, I thought to centrifugally oil the bearings.

I always tend to think that the hard start is to prevent the fan stalling which could happen if you tried to start a fan from cold with low voltage.

[Coolie]

Hi Coolie,
I am not familiar with the system however these are my thoughts on the fault tracing:
You say that you do not think that the thermal cut out is opening as the motor is cold to the touch
Have you confirmed this by measuring for continuity?
Is the thermal cut out (klixon) wired up in series with the power feeding the windings of the motor or does the klixon cut the power to a contactor which may be feeding the motor?

There is no external klixon or contactor for the fan. The fan gets its power straight from the PCB before. A live feed from a 8microfarrad capacitor is connected to the motor too, but not to the main live terminal.
There is an internal thermal cutout inside the motor rated at 170 deg c.

Have you measured the resistance of the motor winding before it cuts out and then also after it cuts out?

I found these readings to be ok.

Where are you taking your voltage measurements, at the motor terminals or at the source of power feed?

At the motor terminals

You say that there is still 240v going to the fan after it cuts out, so then when is it that you get a reading of 60 volts?
I suspect that the 60 volts may be a back emf reading from the fact that the fan blades are not perfectly still.

The 240v I measured after the fan cut out is between phase and earth, the 60v was measured between phase and neutral after the fan cut out. While the fan was running I read 240v between phase and neutral.

How long is the period after the fan cuts do you have to wait before it will restart?

It restarts as soon as the preasure drops low enough for the compressor to kick in.

Have you tried turning the blades manually- do they turn smoothly or are thy tight?

Smoothly

Have you taken amperage measurements?

When the fan kicks in I get about 5 or 6 amps, the running amps are about 2.8 to 3 amps


This is why I get the impression that the thermal cut out inside the motor is faulty

[chillin out]

If you are getting 240v at motor terminal on the live and 180v on the neutral connection then it is not the overload.
You have lost your neutral .
what is the pcb for, do you know for a fact that it`s not a speed controller or doesnt have a currant trip on it (could be a wee electronic part).
As I said before when you go back to site and up all those stairs (ooh the thought makes me cringe) take a h/p switch with you.

hey chemi

The 240v I measured after the fan cut out is between phase and earth, the 60v was measured between phase and neutral after the fan cut out. While the fan was running I read 240v between phase and neutral.

[Coolie]

The pcb is the main pcb for the whole system. The label on the motor says that it is single speed.

Thanks for your help

[Feeze]

Hi coolie,
As I understand it the pcb supplies the neutral to the fan while a permanent live is fed to it via an external capacitor.
So if the pcb cuts out its neutral feed to the fan the voltage should drop theoretically to 0 volts. However. the 60 volts you are reading is the back emf.
Since the live feed is not cut you will still read 240 v between live and ground.
I suggest you investigate the reason why the pcb is cutting out its neutral feed.
You haven't told me if the the internal overload is connected in series with the the windings or if it is used as a control feed.
If it is connected in series with the windings then if it goes open circuit then there would be no continuity when you measure the winding resistance. You claim however that there a reading therefore I would look elsewhere for the fault.
Once again please tell us how is the internal overload connected?
Cheers Feeze

[Coolie]

Im not sure how the internal overload is connected.

The connections to the fan are quite confusing.

There is a live and neutral feed, both from the main pcb.
Then in addition to the main live feed, there is another live connected to a different terminal on the motor. This comes from the capacitor. ( This would obviously be used for starting the fan!)

As it is a six pole motor, there are another three wires coming out of the motor. These are connected to each other. To be totaly honest, I was in a really big hurry and after getting an opinion from a collegue, we both decided to replace the motor!
When I go back to replace the motor, I will have more time to look at it!

I do appreciate your help!

[R W ALLATT]

Did You But A Meter Across The Windings, If So What Did They Read.

[Coolie]

I can't remember off the top of my head, but I can remember thinking that the resistance readings, with all external wiring removed, was ok.
And for the voltage please refer to earlier posts in this thread.

While the fan was running:

Live - Nuetral: 240v
Live - Earth : 240v

After the fan cut out (while the comp was still running) :

Live - Nuetral : 60v
Live - earth : 240v

[Brian_UK]

Just thought Coolie, if the fan is connected to the main PCB is there in fact a fan speed control built-in ? Is there a sensor on the liquid line ? If yes then we have a FSC.

Whether you have or not it does seem as though the neutral is getting switched off via the PCB. I would suggest that you provide a separate neutral line direct to the fan motor and see if the motor runs up OK.

Alternatively, depending on the PCB, see if there is a commissioning plug still in the unit; plug that onto the commissioning pins and the fan SHOULD run at full speed. If no plug then just short the jumper with the blade of a screwdriver.

I have the IMI CD with most of their tech manuals on it so if you can get the model no. I ccan pull the wiring diagrams if required.

[Feeze]

I have the IMI CD with most of their tech manuals on it so if you can get the model no. I ccan pull the wiring diagrams if required.

Brian_UK,
A wiring diagram should clear up the fog.

Cheers,
Feeze

[Coolie]

Thanks, I'll get the mod no from the office today and post it this afternoon/evening!

[chemi-cool]

Chillin-out,

Before you at me, look at the order of the posts.

Still, you must get 240V between phase and ground, if not, be careful, there is no ground!!

One of the most simple ways to find out where the problem is, is to disconnect the fan electrical wires and to energise it from a different electricity source.
If the motor works fine, then the problem is elsewhere, PCB or speed controller or whatever supply the power.

A different motor can be connected to the fan motor supply to see if it runs OK.

Measuring between earth and live as a way to determine the supply to the motor is not practical.

Chemi

[Coolie]

Ok here are the details:

I.M.I.
I think this is the model no. 54200032
Serial No: 0884879
Other details on the name plate: DCUE60 1/50 R407c

Motor:
Make:Elco
Mod 3fgm

Other details on the fan motor:
MCR 203K Air over motor
335-70-6/1
Ins.CL.B 335watt IPH2.6A
230/250V IP23
915 RPM



There was a sticker on the body of the scroll housing:
Torin Part No: AU082084
D.D.C. 241-241
230/250V 50Hz
335w 6pole
1 speed
8MFD

I hope this helps you to help me!


Thanks Chemi, I'll take your advise about checking for power to neutral and not earth!

[chillin out]

CHEMI..

I was only pointing out the fact that coolie had actually used an earth and not the neutral, a lot of people do this ...... I do not.

Although it does tell you more than proving the equipment is properly earthed. It tells you that you have a live feed to the terminal also if you check accros the neutral and earth you can tell you have a proper neutral.
If coolie had checked the neutral to earth I think he might have found 180v.

Therefore knowing he did not have a proper voltage accros the motor he might not have condemed a good motor.

The was not intended to cause offence

[chemi-cool]

The was not intended to cause offence

Its all right, I'm not easily offended. is for a lough, good for your health.

Are you from north Wales?

got some friends there.

Chemi

[chillin out]

Hi Chemi
I live in north wales but come from Scotland.

[Brian_UK]

I live in north wales but come from Scotland.

A-Ah, a true Celt no doubt

[Brian_UK]

Cooie, sorry I can't seem to get a decent copy of the wiring diagram off the CD, if you PM me with your email I can email the pdf copy of the manual. (1.84MB)

As I suspected the fan is driven via a fan speed controller so you could have a fault with a choice of things... PCB or the liquid sensor.

Fan wiring is as:-
wire colour motor - terminal - wire colour to pcb - pcb terminal ref.
White - L - Black - JP9
Black - N - White - JP8
Blue - Z1 - Brown - Capacitor - Neutral

You should find a pair of jumper pins for commissioning use, bridge those to force the fan onto full speed.

Check also the two pots on the pcb for minimum fan speed and temperature setting (I think they are marked R1/R2 or similar).

[BritCit_Juve]

This is one of IMIs electronic units.
On the PCB are two potentiometers, one marked set temp and the other marked min speed. The set temp should be set to maintain around 270psi which is around the 10to location while the min speed should be around 10past. The fan motor is a single speed item but is speed controlled by phase chopping the neutral. There is also a pair of pins marked JP6 which when linked will cause the unit to run the fan flat out. what effect does this have?

The unit in question is I think a DCUE ducted unit so its possible the discharge duct is blocked. This could result in the high ampages you were reading and the motor overheating.
As the unit has been run with the electrics open then the intake grille can be discounted although it should also be checked

[Coolie]

This is one of IMIs electronic units.
On the PCB are two potentiometers, one marked set temp and the other marked min speed. The set temp should be set to maintain around 270psi which is around the 10to location while the min speed should be around 10past. The fan motor is a single speed item but is speed controlled by phase chopping the neutral. There is also a pair of pins marked JP6 which when linked will cause the unit to run the fan flat out. what effect does this have?

The unit in question is I think a DCUE ducted unit so its possible the discharge duct is blocked. This could result in the high ampages you were reading and the motor overheating.
As the unit has been run with the electrics open then the intake grille can be discounted although it should also be checked

The discharge duct is not blocked, I checked and it blows straight outside 31 floors up!! The ductwork is only about 1m long! I was not getting hi amps at all, the max running amps were only around 3. And the motor was cold to the touch, as if it had not been running for days!I dont regard that as being high at all!
When I return I will link pins J6 to see the effect.

Thank you for your help!

[Coolie]

So here we go.

I went to replace the fan motor today.
As I had more time on my hands I could really investigate what the problem was.
I'd like to thank all those who made suggestions as they all came in very usefull.

The first thing I looked at were the two potentiometers. They were both set to the 12 'oclock position. After setting these to BritCit_Juve specs, the fan started running.
Hey presto.

But what caused these "pots" to become adjusted. My theory is that somebody replaced it with one that they oredered as new. As there are a few of the same units dotted around the plant room I think somebody had a PCB go down and when replacing it had the same problem I did, the fan not running. They did not know how to set it and thought they'd nick one that works, thus leaving me with the problem!

It's the only possible explanation! None of our guys had been there for months!

Thanks again guys!

[chillin out]

Thanks Chemi, I'll take your advise about checking for power to neutral and not earth!

Have i changed my name? credit where credit is due, read post 4

[BritCit_Juve]

When powered off most fan motors will rotate backwards due to wind effect and the blade shape. On power up this needs to be overcome as quickly as possible especially when using a slow reacting temperature sensing head pressure control, also untill recently fan motors were hefty brutes that took a lot to get running and have a high stall speed. A hard start is used therefore to overcome these problems.
The min speed pot is there to allow the high stall speed to be taken into account. As a rule every board should be set up for the unit its attached to as different motors and condensing units all have different requirements.
On modern equipment the hard start is becomming less necessary as the coils generate lower resistance thanks to larger areas and fewer rows, the fan motors become smaller and more effecient and the improvements in fan design result in greater efficiency at lower speeds. This has in some cases allowed the hard start and min speed requirements to be done away with altogether especially when using faster responding direct pressure sensing head pressure controllers.
Being a slower temperature sensing design with a heavy duty centrifugal fan and upto a 100pa resistance on the ductwork the DCUE fan motor needs the kick start generated by the hard start and the min speed adjusting to just above the stall otherwise it will sit there humming to itself if the conditions allow!

Hope this helps muddy the waters

BritCit_Juve

[Coolie]

Have i changed my name? credit where credit is due, read post 4

Please accept my dearest appologies!

Thank You, chillin out I appreciate the help!

[chillin out]

Oh it was nothing, no need to mention it really, just glad to help.......but if you are going on the 2nd a gift of the paper kind would be a nice thought

[Coolie]

And now you're pushing mate.... maybe next time!