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

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

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.

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.

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

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.

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

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

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.

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.

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.

I am stuck with 208V, 3 Phase, 4 wire WYE.

I do know that voltage and HZ is not what is needed but one of the strange things is that some of the units have been in service for 6+ months and are working fine, and some others are failing over a few days/weeks.

I sent in some pictures of the units, hope they get posted.

Thanks, Roger

At some level we are all grasping at straws here. You are unfortunately in a situation where you need to make do with equipment that is being applied outside of its specification range.

It may simply be luck that some units work and others don't.

Perhaps the difference between the units that work well and the units that fail is the cycle time on the thermostat.

When an air conditioner first starts up, all of the Freon is at the same pressure throughout the system. The compressor starts and builds up the pressure difference that makes the system work. Once the compressor stops, the pressure bleeds back down to equilibrium.

If you try to _restart_ the compressor while there is still a pressure differential, the motor has to start against a significant load.

Combine this with the low voltage and excessive frequency, and the compressor motor might simply stall.

Perhaps some of the thermostats are cycling off and on too frequently.

-Jon

I for one would like to know what exactly is failing? I assume the compressors. There are a few reasons compressors fail, poor installation and charging mistakes are one big reason. Has the superheat at the compressors been checked, if so what is it? What about the sub-cooling? Delta T? Low voltage is never a good thing for ac compressors. Maybe a buck/boost transformer would be warranted here or you may try and see if some hard start capacitor kits would help. The hard start cap will help a compressor start that is either suffering from excessive vd or starting to fail. Obviously, keeping the condensor coil and evap. coil clean is necessary as well as other basics. I doubt the hertz issue is causing your problem, undervoltage much more likely as well as poor installation practices.

Posted for Afghan Roger

1) Wiring Diagram:





2) Fan Motor:





3) Condensing unit with covers removed:





4)Complete condensing unit:

Since you posted the condenser fan pix I am guessing that is what is going. I put my money on the fan blade having too much pitch. The blade is matched to the motor ... at it's rated speed. If you are running 20% over speed, the blade is working beyond the design load. Try the next lowest pitched fan blade, maybe two sized down it it is close.

e;
What is the current on the fan when it is running?

[This message has been edited by gfretwell (edited 02-09-2006).]

i quickly relized that when i did see the nameplate i say to myself oh oh 208 v 60Hz dont work with this unit at all one thing the relay might not able to pull in right and second thing you will blow the capaictor during starting cycle due low voltage and wrong HZ too that why it keep blowing out the other way is readjust the genny from 1800 rpm to 1500 rpm and change voltage connection go with hi volt 'wye ' connection the voltage between line and netural will fall to right spot after fine tuning the regulator [ i am oringally from France so i know this system pretty well ]
the same with fan motor too it will affect it too


Merci, Marc

Hi Roger,
I've done quite a bit of Air Con work in my time.
Mainly with the Carrier systems.
Sure the fans will run slower as will the compressor, but considering that the compressor motor is immersed in refrigeration oil cooling won't be a problem.
Derating will be an issue though, by this I mean it will have a lesser range of heating or cooling.
I was under the impression that the newer A/C units with the inverter technology could withstand a 20% difference in frequency with all the fans on the indoor (Condensor) and the Outdoor (Evaporator) units using DC motors.

Mike,

with an inverter (variable frequency drive) it would have 3-phase motors would it not? (I agree that they should work independently of frequency)

You can run 50Hz motors on 60 Hz provided that you keep the V/Hz ratio the same. If you increase the frequency, you must increase the voltage by the same ratio.
In your case, 230/50 = 4.6 Therefore at 60Hz, you voltage should be 60 x 4.6 = 276.
If you operate at a lower voltage, the flux in the iron will be reduced and the maximum power of the motor wil also be reduced.
You must also be careful that the increase in speed does not overload the motor. With a pan or a pump, a small increase in speed can give a large increase in power.
see http://www.lmphotonics.com/faq/faq_qanda.php?id=12
Best regards,
Mark Empson
http://www.LMPhotonics.com | http://www.LMPForum.com

[This message has been edited by marke (edited 02-10-2006).]

It would also help this discussion along if Afgan Roger would chime in and tell us what specifically is failing on these units....

Sorry Guys,
Bad guys been a little frisky last couple of days.

The compressors, capacators and relays have been failing, no fan motors have failed as of yet. Reversing valves have also been a problem but I think that one is just crapy materials.

I am fighting with the supplier and trying to get these fixed under warranty and they are saying that because of our HZ being 60 vs 50 that is causing the units to fail. I and my electrical engineer do not believe that is the problem and I wanted some valuable advice from you guys.

Roger

Does the compressor actually have a 208/230 on the nameplate or is it 230 only ? I agree its more the voltage than the hertz. I am not a liscenced electritian but do have almost 20 years in the hvac trade. Even on proper power those units have a tough time starting in some cases, Is there any drop in voltage when the compressor tries to start ? Losing caps,relays and compressors really sounds like they are cycling on overloads on startup untill something goes. http://www.supco.com/ a "start assist/hard start" sp66 or something like that may be all thats needed have had to go that route on many of those even on 60 hz power. Ohh and another tip use the supplied flare nuts with the unit the large one has a thicker end than most and using premade ones or "standard" flare nuts tends to result in leaks when its in the heating mode.

Bad guys feeling frisky? I didn't realise there were any AHJ's in the 'stan! :-)

The nameplates say 230 / 50 Hz, that is what they are specified for. Typically +/- 6%, maybe 10% of voltage, and maybe +/-3Hz of frequency. Maybe additionally a maximum height above sea level is given.

If you run a device out of the range of the specs you'll loose the warranty. That is a law (almost?) everywhere.

So your main issue is just ridiculous to me and not worth any further discussion.

There are some devices that will usually run out of specs without problems but on your own risk. Those obviuosly don't. Some ideas for the 'why?' have been already mentioned.

Another question is maybe if it is possible to prevent future damage for the still running ACs by changes to the hardware. Is this still of importance?

Wolfgang

Afgan, where is the power 208Y coming from?

generator or utility provided?

The units that haven't failed, are they on the exact same power source as the ones that are failing?

Has anyone put a scope meter on the power to see the voltage waveform and frequency?

Dnk...

Thanks for all the help, guess I am pretty much screwed on this one, just as I thought but wanted to run it by you guys. I am going on vacation tomorrow for a couple of weeks, will see how many more fail buy the time I get back. Thanks again, Roger

Bump......

Afghan, you around?

I am curious what you have found here to be the problem.....


Dnk...