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Joined: Jan 2005
Posts: 109
Grover Offline OP
I have a customer with a 10 hp 240v single phase Baldor motor that operates a the hydraulic pump on an industrial trash compactor. The compactor is operated manually, often every 5 to 10 minutes.

About once a year the start winding centrifugal switch contacts (inside the motor) burn up - nasty job to replace them, and severe inconvenience to the customer.

Any thoughts on arc suppression for these contacts? Capacitors? What value?

Thanks for hints and ideas...


Joined: Oct 2000
Posts: 2,722
Broom Pusher and
Might be worth installing a 3 Phase Motor in place of the 1 Phase Motor - provided there is 3 Phase Power available on site.

From the description of "Industrial Trash Compactor", this equipment appears to be installed in at least a Commercial location.
Additionally, one would think an Industrial Compactor would have a 3 Phase Motor driving the Pump - especially with the 10 H.P. Motor rating!

If a 3 Phase Motor is absolutely impossible to use, and this Equipment must use a 10 H.P. 240V 1 Phase Motor, try installing a Motor configuration which applies to the duty cycle.

Some possible reasons for the Start Switch's failure:

* Motor HP is insufficient for the driven Load,

* Voltage at the Motor's Terminals is below / above maximum tolerance,

* Capacitor is shorting out during start,

* Start Switch is not opening completely, contacts are bouncing when opening, or the Switch is opening too late,

* Pump is not "Unloaded" when Motor starts (high head pressure),

* Pump's bearings are tight, or sticking during Starts,

* Personnel running the Compactor are mis-using it (stop, then immediately start in the middle of the compression action; etc.),

* Control system does not allow Motor to stop completely & rest at end of Compression (forward) action, before applying the Pump / Motor to retract the Compression Assembly (reverse).


Take some Ampere readings, along with Voltage readings, at the Motor. Take readings during Starts (forward + reverse) and throughout the entire cycle of events.
Verify the load readings and durations.

Try these tests at different times of the day - such as off-peak AM / PM, mid-peak AM / PM, peak. Perform tests during normal work days.
An event logger would be very useful for these tests.
Just hook it up, turn it on, let it record for a week or two, then read the reports.

Along with the tests, observe the normal operation techniques by the Personnel using the Equipment. See if they are mis-using the Machine.

The problem sounds like an excessive Locked Rotor draw issue.
The Motor could be having difficulty with starts at random times, such as; the Voltage is too low during certain starts, or the Pump is difficult to start.

As mentioned before, the Motor may not be designed for this type of duty, or may be undersized - in Horse Power - for the Pump it is driving.
Verify the Pump's requirements and the Motor's duty cycle.

Lastly, if the Motor is rated for 240V and there is only 208V available, this may be the major issue overall.

Please reply with some feedback.

Good luck.


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!
Joined: Jun 2007
Posts: 301
Whats the model and spec number on the nameplate.

Joined: Oct 2004
Posts: 132
What about changing this to a 3 phase motor powered by a VFD rated for 1 Phase in --> 3 Phase out? 10 HP is pretty big for single there 3 phase available?

Beyond that, everything Scott said is a place to start. If you can, check inrush current and voltage drop, maybe it's getting real low and having a hard time/

Joined: Mar 2004
Posts: 947
twh Offline
By "operated manually" do you mean that the operator runs the ram out until the operator feels like retracting the ram? I serviced one where the operator was stalling the motor. Maybe they need an ammeter with a red-line indicator.

Joined: Mar 2005
Posts: 1,803
This machine has a hydraulic ram, so surely the pressure relief valve on the pump must dump oil to tank before the motor overloads once it's up and running? This must be a starting problem, not operator error.
I agree with other posters that 10hp is a big motor for single phase. Starting it under full pump load is probably the cause of overamperage on the starting contacts. It will momentarily draw at least 120A to start, unloaded. Has it got a startup pressure relief/dump solenoid valve?

Last edited by Alan Belson; 07/22/09 08:12 AM.

Wood work but can't!
Joined: Oct 2000
Posts: 2,722
Broom Pusher and

Any News on the Pump Motor issue?


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!
Joined: Oct 2000
Posts: 2,722
Broom Pusher and
EL-Bump'O #2!!! sick wave


Got an update??? dunno


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!
Joined: Jul 2002
Posts: 8,443
Likes: 3
I was always taught that motors like this weren't designed for "on-off" use.
They were designed for in-frequent starting.
I'd go with the concensus here and say it would pay to install (if possible) a 3 induction motor on some sort of a VSD.
Cage induction motors are more resilient to being started and stopped.

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