Selecting type of 1/2 HP motor for quiet operation and reliability
Selecting type of 1/2 HP motor for quiet operation and reliability
(OP)
I need to select a 1/2 HP motor. The basic service is 1740 rpm, single-speed, 120/240 VAC single-phase, runs 8 hours/day, lightly loaded at 20% capacity except for intermittant 1% duty cycle 2-second long requirements for up to 80% capacity. The motor will be face-mounted into a 30:1 worm gear right-angle gearbox. The environment is room air, ambient operating temperatures 5C - 55C.
Quiet operation is an important feature: unfortunately, instead of a number I've been told "as quiet as you can make it." Oh, joy.
Additionally, the motor will be extremely difficult to access for service, so long term reliability is important with MTBF > 10,000 hours.
I was thinking perhaps a split-phase motor in a TENV enclosure, possibly with a passive convection heat sink? TEFC is tempting, but I'd like to eliminate the fan noise if possible. What made me think of the split-phase motor was reliability: no brushes, and no capacitor. It would be great to eliminate the centrifugal switch, as well: has anyone experience with a start winding that does not need to be switched out, that is, that runs continuously while the motor is powered? Obviously, it would cost some efficency, and increase the heat output.
Lastly, several manufacturers have an option where they will dynamically balance the rotors of your motors to a finer tolerance than is normally done. Has anyone any experience with doing this, and did it appreciably reduce the motor noise?
I'd appreciate your advice very much on how to keep this motor quiet and reliable. I may be quite wrong about specifying a split-phase motor, it's just an idea.
Thank you!
David
Quiet operation is an important feature: unfortunately, instead of a number I've been told "as quiet as you can make it." Oh, joy.
Additionally, the motor will be extremely difficult to access for service, so long term reliability is important with MTBF > 10,000 hours.
I was thinking perhaps a split-phase motor in a TENV enclosure, possibly with a passive convection heat sink? TEFC is tempting, but I'd like to eliminate the fan noise if possible. What made me think of the split-phase motor was reliability: no brushes, and no capacitor. It would be great to eliminate the centrifugal switch, as well: has anyone experience with a start winding that does not need to be switched out, that is, that runs continuously while the motor is powered? Obviously, it would cost some efficency, and increase the heat output.
Lastly, several manufacturers have an option where they will dynamically balance the rotors of your motors to a finer tolerance than is normally done. Has anyone any experience with doing this, and did it appreciably reduce the motor noise?
I'd appreciate your advice very much on how to keep this motor quiet and reliable. I may be quite wrong about specifying a split-phase motor, it's just an idea.
Thank you!
David





RE: Selecting type of 1/2 HP motor for quiet operation and reliability
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If we learn from our mistakes I'm getting a great education!
RE: Selecting type of 1/2 HP motor for quiet operation and reliability
You are certainly correct, thank you! I have only single-phase available, but I've used the trick of 50% derating a small VFD and using it as a single-to-three phase converter in the past with good results.
My fault: I neglected to include that I've been asked to have no silicon in the solution. The only controller is to be a full-voltage starter. This puts paid to my two favorite solutions: a 3-phase squirrel cage induction motor and a BLDC servo.
Thank you for looking at my problem.
David
RE: Selecting type of 1/2 HP motor for quiet operation and reliability
RE: Selecting type of 1/2 HP motor for quiet operation and reliability
They must really not be all that interested in "quiet".
They must actually not be all that interested in reliability nor interested in the obvious ease of automatic multi supply voltage handling or jerkless starting.
I'd challenge the 'no silicon' logic.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Selecting type of 1/2 HP motor for quiet operation and reliability
Many automotive suppliers/shops are trying to eliminate sources of silicone grease contamination, because it plays hell with paint adhesion.
RE: Selecting type of 1/2 HP motor for quiet operation and reliability
All it takes in money.
RE: Selecting type of 1/2 HP motor for quiet operation and reliability
If you can't find a split phase motor with enough torque consider a relay similar to that used in a sealed unit refrigerator (drops out the start winding when the main winding current drops to normal)
Regards
Roy
RE: Selecting type of 1/2 HP motor for quiet operation and reliability
Seriously though, I agree about the PSC motor, especially given the operating conditions you describe. Sounds as though starting torque is not going to be an issue. Look at good quality HVAC motors, they tend to be made for quieter operation because they often end up used inside of air handles where any noise is conducted with the air into office spaces.
You also may want to look in to a permanent magnet synchronous motor, essentially of the type used in clockworks. they tend to be very quiet. Speed may be a problem for that though.
RE: Selecting type of 1/2 HP motor for quiet operation and reliability
ScottyUK, itsmoked, and betrueblood:
We've just concluded a series of acrimonious meetings about the "no silicon" requirement. I lose. No silicon allowed. Thanks for the good thoughts, though. By the way, it was silicon as in chips, not silicone as in grease or enhancements!
CompositePro:
Excellent idea, thanks! It seems that motor noise is related to case mass, so the explosion-proof motors would be the heaviest and therefore quietest of the normal, non-custom motor cases.
RoyDMatson:
The sleeve bearing idea has been very fruitful, thank you! We ran a pair of 1/2 HP motors side-by-side, one with ball bearings and one with sleeves. The sleeve bearing is significantly quieter.
Sreid:
The Permanent Split Capacitor (PSC) motor you've suggested seems excellent; many thanks! If I understand it correctly, the PSC is an ordinary 3-phase squirrel cage induction motor with a capacitor permanently across T2 & T3, and the single-phase input power connected to T1 & T2. The one capacitor serves to both start and run the motor, and is never switched out of the circuit. I have a couple questions on this, if that's alright?
1. Is my description of the connections correct?
2. Starting caps are generally much larger values than Run caps: there is only the 1 cap in a PSC, how do you calculate it's value?
3. My understanding is that for continuous operation the best selection for the type of capacitor would be an oil-filled steel case cap. Other than using a higher-than-necessary voltage rating (e.g. 570 volt cap), is there any other way to increase the reliability of the capacitor?
Thank you again for the excellent idea of using a PSC!
jraef:
You really piqued my interest with your offhand mention of PMSCs as used in clock works! As you can imagine, this technology is no longer in common commercial usage for clocks. I did some searches, though, and found this interesting website about Westclox's AC clock motors: http://c
Thanks again to all of you!
Dave
RE: Selecting type of 1/2 HP motor for quiet operation and reliability
You ask some very good questions most of which I can't answer.
I believe that most PSC motor are simply three phase motors with a capacitor connected to the third phase. I have no Idea how the capacitor is sized. I've always used the capacitor supplied by the manufacturer. Often these would not appear to be of the highest quality. Perhaps other forum members could recomend high reliability types.
RE: Selecting type of 1/2 HP motor for quiet operation and reliability
It is a single phase motor. It does not start as a 3-phase winding.
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RE: Selecting type of 1/2 HP motor for quiet operation and reliability
http:
Now, there are obscure ways to make a 3-phase motor run on single phase using capacitors. I have only heard of this used by hobbyists, not in manufactured applications for industrial, retail, commercial etc. I don't know much about them except I think the caps in conjunction with motor set up a complex voltage divider that gives approx the correct voltage. As far as whether this arrangement is quiet - I'm not sure. I'm guessing it can only be balanced at one load level (after all the motor impedance varies but the cap values don't) and if the 3-phase motor input is not balanced in both magnitude and phase, it's noise will increase.
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RE: Selecting type of 1/2 HP motor for quiet operation and reliability
Curious as to what the prohibition on silicon was for?
Keith Cress
kcress - http://www.flaminsystems.com
RE: Selecting type of 1/2 HP motor for quiet operation and reliability
RE: Selecting type of 1/2 HP motor for quiet operation and reliability
Can you give a few examples?
Keith Cress
kcress - http://www.flaminsystems.com
RE: Selecting type of 1/2 HP motor for quiet operation and reliability
(again, there are people who will try to convert a 3-phase motor to run on single phase... but that is not the intended application when it was manufactured).
I will believe it when I see it.
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Eng-tips forums: The best place on the web for engineering discussions.
RE: Selecting type of 1/2 HP motor for quiet operation and reliability
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I don't know for a fact that the PSC and 3 phase motor windings are the same. I Ohmed the windings once on both motors and the resistance was the same.
RE: Selecting type of 1/2 HP motor for quiet operation and reliability
http://www.filcap.de/pdf/General%20Information.pdf
Anyway, it's good to know that a purpose-built PSC stator does not have 3-phase balanced windings!
More good news: Friday afternoon I got a change order that specifies the motor must be able to start against 80% of it's mechanical load. Nothing like a little change-of-heart to make your day brighter! So, I'm considering one of the configurations that uses a centrifugal switch on a start winding or a start cap. My understanding is that the integral centrifugal switches break often. Since I'm already breaking the budget on this, does anyone have any experience with an external centrifugal switch that has better reliability?
Also, in terms of reliability, I'm thinking that I'd be better off with a start winding rather than a start capacitor. Is this reasonable? Looking for input!
Thanks for all the help with this; I sure appreciate it!
Dave
RE: Selecting type of 1/2 HP motor for quiet operation and reliability
Capacitor start motors may have a partially undeserved reputation for unreliability. There are two basic failure modes;
Capacitor failure; as you have seen, there are grades of start capacitors. Get a motor with a high reliability capacitor.
Start contacts; Contacts wear out related to the number of starts.
Your application appears to be "Start and run for a long time." If this is the case, neither the start capacitor aor contacts will be used much.
RE: Selecting type of 1/2 HP motor for quiet operation and reliability
See bottom of last page:
http:/
Keith Cress
kcress - http://www.flaminsystems.com
RE: Selecting type of 1/2 HP motor for quiet operation and reliability
That's not what a permament split capacitor motor is. PSC is shown in the Leeson link. It has two windings, not three.
As far as I know (someone correct me if I'm wrong), motors are not sold this in this configuration (balanced 3-phase winding with the cap in there to allow single-phase operation). It is a way to reconfigure a nameplated 3-phase motor to run on 1-phase.
=====================================
Eng-tips forums: The best place on the web for engineering discussions.
RE: Selecting type of 1/2 HP motor for quiet operation and reliability
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If we learn from our mistakes I'm getting a great education!