drbond24
Senior Member
- Location
- Barboursville, West Virginia
What can cause an AC motor to stall? Just looking for general stuff right now. I'll get specific later if needed. I'm searching my textbooks (I don't diagnose motors often at all).
The motor is on a pump. The pump is supposed to provide 1700 psi. When the pressure reaches ~1000 psi, the motor/pump stop turning completely and the motor starts pulling over 3 times normal current.
This happens on startup only if the system pressure is already above ~1000 psi. If there is no pressure, the motor starts fine. There isn't a problem until there is pressure.
Have a bit of time now.
In discussing this problem internally, the mechanical people say there is no reason the pump shouldn't turn so it must be an electrical problem. The electrical people say there is no reason the motor should turn, so it must be a pump problem.
I going to guess single phase, cap start, cap run. Good so far?... the motor/pump stop turning completely and the motor starts pulling over 3 times normal current.
.... There isn't a problem until there is pressure.
Have you considered some kind of vent to let the pressure off first? Or a recycle valve to let the pump motor get up to speed?
Jraef said:If you lose voltage, the starting torque that the motor can develop drops at the square of the voltage drop. So if this is happening before the motor finishes accelerating, that will be the case and you will eventually stall. If truly stopped, the current would go to 600%, not 300%, so that indicates it is still turning, just not getting to speed.
One electrical condition that could be happening is if the supply to this motor is seriously deficient, the LOAD that increases with speed as it tries to overcome the existing 1000PSI system pressure is actually causing a severe voltage drop on the circuit feeding the motor. This could be caused by a number of things, none of which we can see from here; conductors are too small, transformer feeding this motor is too small, bad connections that heat up, the list can go on and on. If it were a failing motor, such as a broken rotor bar in the motor or failing motor insulation, it would not likely make any difference that the pressure was already over 1000 PSI as you indicated, so I would rule that out.
Have you taken any voltage measurements while starting? .
iceworm said:I going to guess single phase, cap start, cap run. Good so far?
If so, I have a couple of suggestions.
ptonsparky said:New system? Motors undersized?
kwired said:Check voltage and current when it is heavily loaded and when it stalls.
Is this new or existing? Potential for mechanical problems increases if existing. Could even be motor bearings.
If existing, did this just start to happen or has it always been this way?
Has anything been replaced? Is it the correct motor to drive the pump?
Sorry, got this mixed up with another post in another forum.It is a 575 VAC motor. It does not have dual voltage taps.
What difference does it make to wire the motor wye versus delta?
Lost me here. Looks to me like one would be connecting 332V coils across 575V Severe overvoltage. I don't see how the LRC would be reduced - should go up - saturatedSorry, got this mixed up with another post in another forum.
But it would make a similar difference if it was supposed to be connected in Wye for 575V, as is likely the case, and you connected it in Delta instead, which would be the equivalent of connecting it to 332V. Same net effect as far as the motor goes and the LRC would also be reduced.
The motor is on a pump. The pump is supposed to provide 1700 psi. When the pressure reaches ~1000 psi, the motor/pump stop turning completely and the motor starts pulling over 3 times normal current.
This happens on startup only if the system pressure is already above ~1000 psi. If there is no pressure, the motor starts fine. There isn't a problem until there is pressure.