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skyesparky
23-08-2013, 12:48 PM
Hi Guys, Hoping you can help. A friend of mine who runs a shop has been having problems with a Koxka? display unit. Around six months ago the 4 motors packed up due to the drain being blocked and water getting in the motors. A local engineer had a look and replaced the original motors with elco replacements. The originals were 34w and the replacements are only 18w. Engineer said that replacement 34w motors wouldn't physically fit. (apparently the originals had a much shallower depth)

The problem now is that the motors just aren't pulling the temp down enough. We have tried to find exact replacements but to no avail. These are the motors that are in place now http://www.ryanairconspares.com/motor-fridge-rymfit-watt-multi-universal-refrigerator-p-817.html

The original engineer is not willing to help at all and took the originals with him (hence why ive been asked, im not an engineer but a sparky)

I cant find a 34w motor with the same depth as the one shown above. Any help would be much appreciated.

passandscore
23-08-2013, 01:09 PM
You could always try contacting Koxka's sales office and ask them. They should be able to assist you.

Contact info is on the last page of the provided link.
http://knudsenkoling.dk/files/system/PDF/Koxka_Superette.pdf

r.bartlett
23-08-2013, 02:15 PM
firstly that is theft so he should be careful about not returning them. secondly why did he not replace them ??

al
23-08-2013, 07:20 PM
I've not come across such a large motor fitted to an evaporator except in a cold room. Koxxa is your best bet for an original replacement. Just playing devils advocate, the blades are on the right way and spinning in the right direction? Is there something else wrong that it is not cooling?

alec

Rob White
23-08-2013, 10:13 PM
.

You say it happened six months ago?

Did it work OK after the fans were fitted and now doesn't?

The fans create air flow and if they are not working then the coil
would tend to ice up, but other things cause the coil to ice up.

This fridge needs checking over, don't just assume the fans are not
working correctly.

Regards

Rob

.

monkey spanners
23-08-2013, 10:36 PM
If it is a dairy deck style fridge, remove all the shelves and back panels and clean them, dust blocks the holes, also there will be some grills at the top at the front, clean these too. The fact the drain blocked up in the past points to your customer not maintaining the equipment properly. Make sure the evaporator and condenser are clean too!
As others have said Koxka would be the best place to start with replacement motors, failing that Polestar might build some to the correct spec for a charge.

Pole Star
11-10-2013, 02:45 PM
Really must check the forum more often *slaps self on the wrist.

I am sure by now your will have managed to find a suitable replacement.

I will reply purely because of the comment you made about the engineers suggestion of swapping the 18W for a 34W....


I personally have somewhat of a love hate relationship with multi-fits. Since they fit so many applications by nature they often cover up a multitude of sins. On problems applications such as this where the temperature is not being pulled down down enough we tend to find its prudent to check the the blade diameter. A mismatch of motor power and blade diameter will cause no end of issues in itself including premature failure of the motor.

Assuming the original motor was 18W (like the multi-fit that was removed) it is likely to have had a 230mm - 254mm blade diameter, rather than increasing the motor power it is best to first increase the pitch of the blade as this yields a far greater performance increase. Changing for a 25W would have been the second option but a 34W motor on a 230mm for example would have simply ended in a failed motor in 6months, bearing failure due to overheating.


BR
Pole Star

nike123
11-10-2013, 04:21 PM
Not directly connected with this subject, is there any literature which explains how to select these fans and how to size their motors regarding diameter and blade numbers and angles etc...

It is pretty unclear field to me and it looks that I need more knowledge at that particular field.

Pole Star
11-10-2013, 04:39 PM
Not directly connected with this subject, is there any literature which explains how to select these fans and how to size their motors regarding diameter and blade numbers and angles etc...

It is pretty unclear field to me and it looks that I need more knowledge at that particular field.

We list in our general spares book and our shaded pole leaflet our recommendations as to the maximum blade diameter and pitch we would suggest per motor power.

If you go to page 9 - http://psp.uk.com/pdf/multi_fit_fan_motors.pdf
Mod - not sure what the rules are for linking so please remove if its an issue, I tried a screen grab instead but the resolution was too poor to see clearly.

The above link is what we suggest, we do however have a couple of OEM's who run with a couple of exceptions to the rule in order to achieve a specific airflow. But it impacts upon the motor life (not massively but it is a sliding scale.

Its true to say a 5W motor on a 300mm blade is just as bad as a 34W on a 154mm. Both will fail early.
The 5W will burn out due to having to work too hard to drive an over sized blade, whilst the opposite case the 34W will fail as the airflow from the 154mm blade is not sufficient to keep the motor cool.

Likewise other considerations when replacing an OEM motor with a multi-fit is the angle of motor operation.
95% of multi-fit motors are sleeve bearing and as such should only be used when in a mounting angle of 45deg off horizontal. Any that are vertically mounted should be replaced with a ball bearing motor. A sleeve bearing needs the end float in order to stay lubricated, beyond 45 deg this doesn't occur and the motor will fail prematurely.

nike123
11-10-2013, 04:46 PM
Thanks for quick response! In meantime I have already found your web site and downloaded multi fit PDF.;)
Just studying!

nike123
11-10-2013, 04:53 PM
Nice informations in that booklet. Unfortunately it is missing what is airflow created with these motor, fan blade diameter, fan blade numbers, and blade pitch combinations.
Any suggestion where I could find that information or guide how to calculate from these input data's?

Pole Star
11-10-2013, 05:00 PM
Nice informations in that booklet. Unfortunately it is missing what is airflow created with these motor, fan blade diameter, fan blade numbers, and blade pitch combinations.
Any suggestion where I could find that information or guide how to calculate from these input data's?

The above is a general guide so you know the limitations and don't miss match blades and motors.

For actual performance charts you won't find a general purpose graph. Each manufacturer has slightly different performance, we obviously have full curves for all our motors and blades but we don't list them all in one place (there would be far too many!). If there was a specific size you was interested in I would be able to show you ie 10W motor, 200mm blade, 34 deg, plastic ring & plastic blade.

A few other things you might not realise but a plastic blade generally is 5% more efficient and also around the same percentage quieter than an aluminum blade.

nike123
11-10-2013, 05:02 PM
These are first results of my digging:
http://robots.dacloughb.com/wp-content/uploads/2012/02/flowfans.pdf

nike123
11-10-2013, 05:07 PM
The above is a general guide so you know the limitations and don't miss match blades and motors.



I want to be able to determine what diameter and motor power and pitch etcc., I need when I have, for example condenser, of some determined capacity with requirement of 100m3/h of air flow.

Tayters
11-10-2013, 09:59 PM
Cripes, never really thought that much about these motors before, especially fitting a larger one with a smaller blade which could knacker the bearing.

Some interesting stuff there, spank yer hairy crutch!