230VAC 60Hz Single Phase Motor running at 50Hz?

[Zucca]

It is not the first time a funny guy like me ask this questions (kind of):

https://www.eevblog.com/forum/beginners/what-happens-when-you-run-a-50hz-3-phase-motor-at-60hz/

anyway I wanted to start a new topic with much more details, on top of that for a single phase motor there is nothing here.

Good readings:

http://www.usmotors.com/TechDocs/ProFacts/50Hz-Operation-60Hz.aspx

http://www.engineering.com/ElectronicsDesign/ElectronicsDesignArticles/ArticleID/8154/Changing-an-Induction-Motors-Power-Supply-Frequency-Between-50-and-60Hz.aspx

in the last link I am confused by this obscure procedure:

If the machine can run 20% slower there may still be hope.  Even though it is going to lose cooling with its internal fan running more slowly, running the load slower and with a 20% less powerful motor will likely even out. The V/Hz increase may still get you.  At this point if your assessment shows you will probably be alright with the slower speed, again check the nameplate for the FLA.   Run the machine and quickly check the running current with an ammeter.  If it's below FLA proceed to load the machine while closely monitoring things.   If you stay below FLA it will probably be OK.

too risky IMO... The interesting part in this last article is the "Single phase motors start winding", which can result in a immediate holy smoke circus.

Now my story, I got a cheap air compressor here in USA (I couldn´t resist), and since I will soon move to Europe I thought let´s just take care about the voltage who cars about the frequency it will run just slower.

FAILED (I think).

Here the (induction) motor (sorry about the quality, I´ll do a better shot later):



should be this one:

http://www.srvcelectricmotors.com/products-page/air-compressor-motors/century-ao-smith-electric-motor-b385-5hp-spl-3450-rpm-56-frame-208-230vac/

I think I will sell this motor here in US and buy a new one in Europe. (I will vote for that.)

Any suggestions? You can vote in the pool above. Let me know if I need to add another option...

[Zucca]

I contacted http://www.centuryelectricmotor.com and ask if I can run it at 50Hz. Let´s see.

[richard.cs]

At nominal voltage and 50 Hz it will probably saturate, draw lots of current and die. If it's a very generous design (unlikely on a cheap compressor) it might be ok but will definately run hotter.

You should reduce the voltage in proportion to the frequency to keep the peak flux in the iron the same. It will run at reduced speed (5/6th) but the same torque if you run it on 230V*(50/60)= 190V. You could do that with a small small transformer with a 40V output, wired as an autotransformer to drop the incoming 230V (ish, depends where you are) to 190V. On a compressor this reduced performance should be fine.

[calzap]

Curious to know what brand of compressor you bought and whether it is an oil-less type or one with a crankcase.  The former are usually have a direct drive and are constructed of light-weight aluminum, whereas the latter  usually have a belt drive and are of cast iron and steel construction.  The oil-less types are usually cheaper, noisier and don't last as long.  If you have one of the oil-less types and given the possible motor problems, I advise cutting your losses and sell it before moving.

Compressor motors have one other starting consideration that motors for many other applications don't face and that is the need for a good unloading valve.  This valve allows the motor to start at low or no back-pressure before it faces driving air into a high pressure environment, usually a tank.  Cheaper compressors usually have poorer quality unloading valves. Poor performance of an unloading valve puts extra starting stress on a motor which would be added to stresses of suboptimal voltage and frequency.

By the way, in the USA at least, motors labeled at 230 VAC are expected to receive 240 VAC, and motors labeled for 115 VAC are expected to receive 120 VAC.  I'm not sure why motor voltages are stated below actual mains voltages, perhaps it's historical, perhaps to account for average voltage drop of wiring runs.  Does anyone know?  It that also the case in other countries?

Mike in California

[Zucca]

Curious to know what brand of compressor you bought and whether it is an oil-less type or one with a crankcase.

It is a oil one (BTW which oil I need to use?), this one:



25 gallon tank, max PSI 120

[SeanB]

Oil is ordinary motor oil, preferably a synthetic 15W30 oil, or a straight SAE30 mineral oil or a multigrade 15W30 engine oil. All will work well in the compressor, though if you want to you can buy Ingersoll Rand T30 Select compressor oil for reciprocating compressors at a premium, as it will work here nicely. If you want a brand buy Mobil One engine oil, 2 quarts will probably be enough to refill the compressor.

You probably would be better off though buying a new compressor in Europe though and using it there. Remember that as it is a vessel under pressure you will need to have it certified for pressure at regular intervals. Can be a pain and often people just toss it and buy a new one instead for the small cheap units.

[Zucca]

This one should fit:

http://www.ebay.de/itm/Elektromotor-230-V-2-pol-Motor-fur-Kompressor-Schweranlauf-Wechselstrom-/311151446246?pt=Motoren_Getriebe&var=&hash=item48721248e6#shpCntId

BTW: You guys are awesome, I am learning so much.

[donpetru]

 If you try using a 60Hz motor in 50Hz then you must know:
a) the motor it will turn 20% slower.
b) the cooling will drop dramatically.
c) the load's horsepower requirements will drop, possibly dramatically. The motor's hp will drop because hp is a function of speed x torque.
d) V/f will increase possibly causing a large increase in current draw. The most serious issue is the V/f issue. So, if the V/f will increase.  Likely enough to cause a large increase in the motor's current.  This coupled with the reduced cooling may cause rapid overheating.

[NiHaoMike]

Just use an autotransformer to drop the voltage to 200V or so.

[calzap]

The 5 HP rating is probably a bit exaggerated.  Note that the motor plate for HP just states SPL (split phase).  Generally, single phase induction motors draw about 5 A per HP; so the 15 A motor is probably about 3 HP.   Don't know that the "SPL" would change it much.  One website (wisedan.com) says SPL means Someone's Probably Lying!   In the US, compressors and vacuum cleaners are notorious for overstating HP.  Often the HP used in advertising is based on the starting current draw or locked rotor draw rather than steady state current.  Usually there is some fine print on the machine or in the manual that states the HP is "peak" HP.  There was a class action lawsuit that was supposed to end the lying, but it didn't.

Mike in California

[Zucca]

The 5 HP rating is probably a bit exaggerated.  Note that the motor plate for HP just states SPL (split phase).  Generally, single phase induction motors draw about 5 A per HP; so the 15 A motor is probably about 3 HP.   Don't know that the "SPL" would change it much.  One website (wisedan.com) says SPL means Someone's Probably Lying!   In the US, compressors and vacuum cleaners are notorious for overstating HP.  Often the HP used in advertising is based on the starting current draw or locked rotor draw rather than steady state current.  Usually there is some fine print on the machine or in the manual that states the HP is "peak" HP.  There was a class action lawsuit that was supposed to end the lying, but it didn't.

I saw a Sears/Craftsman one with 6HP but rated current 15A and voltage 230VAC . Yes I smell gold plated BS in the (compressed) air.
I think with a (real) 2,2KW motor I can save the galaxy.

[SeanB]

A real 2.2kW motor is more likely a 3kVA unit, and even if built with a lightweight frame will be over 30kg. It will not fit that frame at all, so likely the actual motor is a 1.2kVA unit which is "Chinese Export spec" and which will fail after 100 hours or so of running from either burnt out windings or dead bearings, a toss up which comes first, but the running at just under glowing aggravates the bearing failure.

As they only cost $100 new here I would recommend just selling it in the states and buying a new European sold unit, you will have the same compressor, same tank but a different set of pulleys and a warranty of sorts under EU law on the tank exploding from being faulty.

[Zucca]

Thanks SeanB I did not know that. So there is no hope to know the real power of a motor without a specific test bench.

Can you suggest me a 50Hz good motor to replace that 60Hz one? Or should I just accept my mistake and sell the unit I just bought... 

BTW I plan to use the compressor 2/3 times a year worst case. I don´t need to get something rock solid for a car shop use. So if I need something just sporadically I want a gear that get the job done and low money as possible.

Take care and thanks in advance for helping me.

[SeanB]

Sad thing is a new motor ( FEW or Bonfiglioli) will cost almost as much as the whole unit. As well you will need a smaller pulley on the motor to compensate for the slower running and this may or may not be within the adjustment range of the compressor mounting bolts.

If you are going to only use it 2-3 times a year for a short while just use as is, and plug it into a 10m 1mm extension cord, as this will drop the mains voltage enough to keep the motor happy. Just do not leave the cord rolled up, leave it in a big spiral on the floor to keep it cool. that way if the motor survives a year or two you will have gotten value out of it, and if it cooks you take it to Bonfiglioli ( as you are in Italy and that is where they come from, but the motor will likely come from Vietnam) and ask for a new one that fits, then take the old one and strip for the copper, steel frame and such.

[johansen]

first off that's not a 5 hp motor so you're going to get burnt.
a finned heatsink wrapped around the core of the motor might help you out.


I suggest reducing the pulley diameter to drop the power consumption another 20-30%

[Zucca]

Here the response from http://www.centuryelectricmotor.com

Hi xxxx, This motor is not suitable for 50 cycle operation.  Regards, xxxx
 
XXXXX
Regal Beloit America, Inc.
Tipp City, OH 45371 

and thanks to you guys now I know why.