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#61957 - 02/07/06 02:51 AM 50HZ vs 60HZ  
Afghan Roger  Offline
Junior Member
Joined: Jan 2006
Posts: 9
Aloha, Oregon, USA
Lookinf for opinions please. We have a large number of split type air conditioners and they are rated for 220V, 50 HZ. We are running them on 208V, 60HZ. We are having several failures and the manufacturer rep is convinced the HZ is the reason they are failing. Our electrical engineer does not agree with this and belives that is not the problem, gan I get some proffessional advice from you guys?

Thanks, Roger


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#61958 - 02/07/06 03:02 AM Re: 50HZ vs 60HZ  
RODALCO  Offline
Member
Joined: Dec 2005
Posts: 854
Titirangi, Akld, New Zealand
Hi, I think that you have 2 problems here.

The lower voltage is more a bit of a problem because at the lower voltage the motor hasn't got all the torque available to start into the load.

It may stall and humm and eventually burn out or get very hot till the insulation fails at some stage.

Check with the nameplate as the higher frequency has the motor run at a higher speed and the compressor may not be designed for it. e.g. a 1500 RPM motor at 50 Hz will run at 1800 RPM at 60 Hz and may cause the compressor to run hotter.

good luck Ray


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#61959 - 02/07/06 03:46 AM Re: 50HZ vs 60HZ  
e57  Offline
Member
Joined: May 2003
Posts: 2,876
S.F.,CA USA
Need some more info on this, 3-phase or single?

Voltage and system (wye vs delta) would be more of an issue than freq'. Most motors will survive a differance in Hz with no problems. Many are dual rated. The refridgerant also does not know the differance, plumbing wise, it will act the same.... If using 3 phase motors they could be re-connected to compensate for voltage, etc. Some motors will fail to start, or have reduced power with the wrong source. (wye vs delta)


If you dont mind... when you say "split type air conditioners", do you mean seperate compressor and evaporator? If so, more often than not it is a leak in the coolant system. Do the units have refridgerant indicators? (Little glass bubble with a green - full - dot, or yellow - empty - dot in the middle) Reffer compressor motors also burn up when they are empty. The refridgerant acts as a lubricant and without it, it over-works the motor.


Mark Heller
"Well - I oughta....." -Jackie Gleason

#61960 - 02/07/06 05:42 AM Re: 50HZ vs 60HZ  
C-H  Offline
Member
Joined: Sep 2002
Posts: 1,497
Stockholm, Sweden
The voltage works against you in this case. A motor that runs on 200V, 50 Hz will be just as happy with 240V, 60 Hz but run faster.

Can you reduce the power demand or raise the voltage somehow? (Changing gears between the compressor and motor, e.g.)

Another idea would be to deactivate the thermostat and run the AC on a timer: With an intervals short enough to give some cooling but not long enough for the motor to burn out.


#61961 - 02/07/06 10:30 AM Re: 50HZ vs 60HZ  
Afghan Roger  Offline
Junior Member
Joined: Jan 2006
Posts: 9
Aloha, Oregon, USA
The split type is where the compressor and condenser are outside and the evaporator is mounted inside with refrigerent lines connecting. 20,000 BTU cool/heat.

We are supplying 208 3 phase wye system.

No sight glasses on the units but gauges are reading normal. We have had some leaks but that is not the current issue, they are charged properly and leak checked.

Thanks, Roger


#61962 - 02/07/06 10:46 AM Re: 50HZ vs 60HZ  
renosteinke  Offline
Cat Servant
Member
Joined: Jan 2005
Posts: 5,316
Blue Collar Country
Afganistan has been referred to as "the roof of the world." Keeping this in mind, altitude may be your problem.

Over about 4000 ft, you need to take the thinner air into account in two ways. First, motors will not be cooled as efficiently; this is compounded if there is little humidity.
Secondly, a different table is used in charging the system with refrigerant- with the result of there being 'too much' used, and everything suffering.


#61963 - 02/07/06 12:21 PM Re: 50HZ vs 60HZ  
winnie  Offline
Member
Joined: Sep 2003
Posts: 649
boston, ma
IMHO C-H has described the key problem.

The motors in these units are _probably_ induction motors. The magnetic field strength in an induction motor is directly proportional to the applied voltage, and _inversely_ proportional to the applied frequency. These motors are being operated at about 72% of nominal magnetic field strength. This reduces the _peak_ torque that the motor can produce by about 50%.

At the same time, these motors are going to try to spin at 6/5 normal speed, which will _increase_ the torque required by the compressor pumps. Depending upon the application, the torque required by a pump will increase as the _square_ of shaft speed, though I don't know if this applies for AC compressors. Certainly the torque required will be going up substantially.

IMHO you are behind the 8 ball. The motors will be producing less than rated torque. The compressors will require more than rated torque.

If you boost the voltage high enough to properly magnetize the motors, then you may run into issues with the maximum voltage of the control system, and life issues with the pumps running faster and at higher pressure. Or you might just get the system to run reliably in a somewhat 'supercharged' fashion [Linked Image]

Reno's points about cooling and charging are relevant, but IMHO second order effects. Solve the voltage problem first, the frequency problem second, and the cooling problem third.

Just MHO. I'm not out there in the field.

-Jon


#61964 - 02/07/06 02:14 PM Re: 50HZ vs 60HZ  
rad74ss  Offline
Member
Joined: Apr 2004
Posts: 156
Pryor, OK USA
Check the motor nameplate first to see if they are rated for 50/60. The main problem with running refrigerant compressors at abnormal speeds is that it changes the compression ratio drastically. This leads to lubrication problems and major differences in the design performance of the system.

Also check the units for control circuit transformers. If the unit has them to drop the 220 down to 115 or 24 volts you may have a problem with the voltage on the secondary dropping too low. Some devices will not operate if the control power drops too far. We have certain digital controllers that will simply deactivate themselves rather than run on errant voltage.

You might try to contact the Orignal Equipment Manufacturer and ask them to run a balance on these units at 208/50 and see if it should run on that and what effects that operating voltage and hertz will have on your performance.


#61965 - 02/08/06 10:08 AM Re: 50HZ vs 60HZ  
Texas_Ranger  Offline
Member
Joined: Dec 2001
Posts: 2,400
Vienna, Austria
Were there any diagrams supplied with the units? If so, do you have a way of posting them here?
220V 3ph seems to indicate 220/380V wye to me, if you only have 220V between phases the motor would have to be delta connected (and I mean ungrounded delta).
If you're referring to the generator fed locations you talked about in the other thread I have a strong feeling the easiest thing would be to get a 230/400 or 220/380V 3ph 50Hz generator set and run them as intended.


#61966 - 02/09/06 07:13 AM Re: 50HZ vs 60HZ  
C-H  Offline
Member
Joined: Sep 2002
Posts: 1,497
Stockholm, Sweden
A boost transformer from 208 to 240V might help a little.

Ragnar's idea isn't bad either. If you have a 277/480V source, maybe you can wind them in Wye (220/380V) and run them on the 480 instead.


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