Mixer Motor.
Mixer Motor.
(OP)
Hi,
New to the forum and was seeking some help with a problem I have. We have received a Mixer Motor back from a client and on inspection the motor seems o.k. We have identified the 3 windings, checked resistance and all seems well. When you run the motor out of the water it runs o.k then as soon as it is installed in the water it ramps up and down from between 5 and 40 Amps. The motor is a 440v 50 Hz and is connected in Delta the FLC is 12 Amps. We tried all different configurations of the 6 cables but nothing seems to work. Any help would be greatly appreciated.
New to the forum and was seeking some help with a problem I have. We have received a Mixer Motor back from a client and on inspection the motor seems o.k. We have identified the 3 windings, checked resistance and all seems well. When you run the motor out of the water it runs o.k then as soon as it is installed in the water it ramps up and down from between 5 and 40 Amps. The motor is a 440v 50 Hz and is connected in Delta the FLC is 12 Amps. We tried all different configurations of the 6 cables but nothing seems to work. Any help would be greatly appreciated.





RE: Mixer Motor.
Can you correlate the amperage swing to the output shaft position?
RE: Mixer Motor.
Will check,there is no gearbox all it has is a propellor, just seems strange how it works ok out of the water and even just skimming on top of the water suddenly jumps to 30 to 40 amps then flucuates.
RE: Mixer Motor.
RE: Mixer Motor.
Is this a manufactured mixer or has someone taken a mixer meant to be turned by a 1/2" drill motor and mounted it on a 10 HP motor?
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Mixer Motor.
P.S
Winders assure us the motor is wound o.k.
RE: Mixer Motor.
Also if possible compare sudden application of load to gradual application of load.
One longshot that comes to mind is torsional resonance of mechanical origin or electromechanical origin. What is the speed of the motor and what is the speed of the oscillations? How big is the prop?
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RE: Mixer Motor.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Mixer Motor.
You have connected the motor incorrectly. You said it "is a 440v 50 Hz and is connected in Delta the FLC is 12 Amps".
That is highly unlikely, a 50Hz motor is almost always 380-415V, 440 is usually a 60Hz motor. If it is a 440V 60Hz motor and you connected it incorrectly, you not only have 57% of rated torque, but the speed is slower as well. Uncoupled, it will spin at the speed of the frequency and poles. But as soon as you put a load on it, it is going to go into high slip and stalling. In a centrifugal propeller pump, load is speed dependent. So as you begin to stall it, it slows down, which sheds load, which allows it to speed up, which couples load, which puts it back into high slip and near stall, repeat ad nauseum.
Describe all of the motor connections and the EXACT nameplate data for additional help.
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RE: Mixer Motor.
Keep in mind that the wires could be mislabeled too.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Mixer Motor.
If you'all will indulge an attempt at analysis – that scenario doesn't make sense if we anaylse it using the steady state torque speed curves:
If we plot the motor and load torque speed curve vs speed
There are two types of intersections of the torque speed curves:
1 - a stable intersection occurs whenever load curve slope exceeds motor curve slope. Once you get to this point, you tend to remain there.
2 - an unstable intersection occurs whenever motor curve slope exceeds load curve slope. The machine tends to accelerate away from this type of intersection in either direciton.
If you draw the two curves in almost any way imaginable, the intersections must alternate: stable, unstable, stable, unstable. To see-saw back and forth would require two unstable intersections next to each other – difficult to imagine.
But as we have discussed before, the steady state curves don't always tell the whole story.
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RE: Mixer Motor.
The prop is spinning too fast. It may be the wrong prop for the motor, or the motor may be a 3000 RPM base motor and the prop may be designed for 1500 RPM base speed. (Or 1500 RPM and 1200 RPM).
Such a mismatch may alternate between overload and cavitation.
This is not to dismiss jraef's theory which may also be investigated.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Mixer Motor.
Muthu
www.edison.co.in
RE: Mixer Motor.
I believe that the two intersections you speak of may exist but both are mechanically or hydraulically unstable.
The high current intersection may cause cavitation which will reduce the load. The result will be low current. Cavitation, once started may continue, however, should conditions be such that cavitation ceases, and the prop "Grabs water", the current will again go high. Does this reconcile your suggestion with some of the other suggestions made here?
Yours
Bill
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Mixer Motor.
Caledonia - You did say the problem occured both at the customer's site and at your shop? In that case I guess it rules out power supply problems.
What about a rotor bar problem? That causes current oscillation. I haven't heard of the oscillation being as severe as you described, but who knows. Try a single phase test.
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RE: Mixer Motor.
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RE: Mixer Motor.
But it leads to another question - did this surging occur at the customer's plant and the shop, or just at the shop? Was the customer running it with water?
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RE: Mixer Motor.
Regards
And thanks again for all the replies.