doubleshaft electric motor driving hydraulic pumps

[mike1969]

I'm having a problem with a 75kw doubleshaft electric motor, it drives two hydraulic pumps and when these pumps reach their high pressure the motor is drawing 200+ amps (it is rated at 118A @460vac) this situation only lasts for a second or two at a time, but it happens 10-12 times a minute and the motor is really heating up as a result. the equipment is an aoki sbIII 1000nl 300 blow mold machine to make plastic containers, I ran the motor alone disconnected from the pumps and it draws 42A @460vac. we just rewound this motor for the customer and I don't think we have a problem with our work, though I'm open to any suggestions-- I just want to find the reason for the high current and correct the situation. can anyone offer any help with this? it would be greatly appreciated. anything I should be looking at in particular with the pumps?

 

[waross]

Dis someone crank up the hydraulic pressure?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[MikeHalloran]

It smells like the relief valves on the pumps have been jacked up past the system design pressure in order to get more clamping pressure to compensate for a mold flash problem.
You may need to install tamper-resistant covers on the valves, or initiate disciplinary action.

Oh, and get a moldmaker in there to fix the molds, and a tech from the machine builder to detect and undo any other unauthorized changes.

Get the motor checked out, too; 42A unloaded sounds like a lot without seeing the spec sheet.



Mike Halloran
Pembroke Pines, FL, USA

 

[mike1969]

maintenance guys in the plant told me nobody touches those valves, but i have no referene to where they should be set at. the "tech" manuals they have are little more than sales pamphlets. 42 amps no load is not high for this motor at all, its just a little over a third of rated amperage which is fine. i will check on those relief valves tomorrow and see if i can get any info about possible changes-- at least its something to start with and i appreciate the input

 

[waross]

That may be a special motor, but the special design may be in the rotor.
Did you rewind based on the existing winding or based on a generic 75 HP spec?
Is this a common design "B" motor?
Injection molding machines may use design "A" motors.
I suggest checking with the machine manufacturer to see if the motor is still the original motor and checking with the machine manufacturer and the motor manufacturer as to the application and allowable momentary overload.
As for momentary overloads you may find the information on RMS HP loading on .pdf pp49 of the Cowern Papers helpful.

http://www.baldor.com/Shared/manuals/PR2525.pdf

If the motor was selected based on RMS HP loading and the machine timing cycle has been changed, there may be issues.
How hot is the motor?
A motor surface temperature may be too hot to comfortable feel and still be within safe temperature limits.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[77JQX]

I'm not sure what design the "hydraulic pumps" are, but many pumps require the most horsepower, and motors the most current, when the pressure is low and the flow is high. Does the high amperage correspond to the times the molds are being filled? I suspect too much flow, not too much pressure, is the cause of your high amperage.

 

[waross]

Design "A" and design "B" refer to the motor.
You are describing the characteristics of centrifugal pumps.
If the current is peaking the pumps are probably positive displacement. Current and HP will increase with pressure.

Bill
--------------------
"Why not the best?"
Jimmy Carter