Inverters

Hi All, This is my first Thread so please excuse anything I do incorrectly.

I have a Tom Senior mill with a Brook Crompton 3ph 750W 1hp motor which I am trying to run using a Mitsubishi E500 inverter I have followed the instruction in the motor and made the wiring correct, but the inverter keeps alarming out with motor over load or over heating. I have played about with things and it runs ok now but the motor seems to be getting a little warm.

Any ideas gratefully accepted?

Hello Andrew,

Welcome to the forum. I'm not familiar with programming the Mitsubishi inverters, but it should be possible to go through and note all the settings you have changed. You can then reset it to factory settings (which should give basic performance with a standard motor with no problems) and see if any of your tweaks cause problems when you put them back in.

As for 'a little warm' its not unusual for motors to run warm, especially when run below normal speed, an advanced inverter will make assumptions about the motor and shut down or reduce power if it thinks the motor may overheat. But do be aware that the motor may well be hot enough that you don't want to put your hand on it and not actually be overheating. My class B motor can take a 110 degree temperature rise... not that I want to run it that hot!

Neil

Andrew, can't help directly with the overload trip - but as Neil says it sounds like it may be a mismatch. Concerning the motor (over)heating, one aspect you need to beware of when using a variable-frequency inverter is not-only over-speed but also, if you run it much lower RPM than it would at normal mains frequency, if it has a shaft-mounted fan that may now be running too slow to cool the motor properly and you may have to arrange separate forced ventilation that's not shaft-speed dependent.

Dave

Andrew,

I work with Siemens inverters and submersable pumps and occasionally we have to change a pump, occasionally we get a motor overload alarm like you describe and its caused by the fact we have forgotten to set the motor amperage correctly in the inverter parameters, regarding the getting warm I agree with neil, if your running the motor below its normal speed it will warm because the fan is moving enough air, you could overcome this by fitting another, electric, fan which runs at its own speed cooling the motor.

Martin P

Firstly is the motor a dual voltage (440v/240v) unit ? It should say so on the makers plate. If not and its only a 440v motor then your inverter might not run it. Also is the motor itself wired correctly ?  Eg star or delta for the appropriate voltage. If you try to start the motor too quickly it might cause the inverter to trip out, maybe change this parameter.  These questions might be simplistic or basic , but normally inverters and motors are easy enough to wire up and usually work very well from the get go.   

Edited By ronan walsh on 19/11/2014 22:34:27

On my 1954 M1 the motor was 415v (Star) only, I had to open it up and pick out the Star point in the windings to convert to 220v (Delta).

It now runs fine on a Teco 1HP invterter.

Is your Mitsubishi inverter 415 or 230v output?

Paul

Actually a 440V motor can be run successfully on 220V. One of my shapers, an 18 inch Alba, has a 3hp motor which is nominally 460V, and is Delta connected as standard, meaning I can't restrap it for a lower Voltage. One interesting experiment that I have tried is running it from a 230V inverter. It runs fine. Naturally the maximum power is less, but even with only about 3/4 of a horsepower available the machine can remove metal pretty fast. (Running single phase motors on reduced Voltage is not a good idea, they can burn out the start winding if they don't get fully up to speed.)

But that is not the original writers problem. Usually the motor should not run any hotter with the inverter than it would normally. With modern insulation that can be pretty hot. There can be a problem when you run slow for extended periods, especially with a heavy load, since the fan in the motor will be running slow too and will be less effective, as mentioned by two posts above. The heat generated in the motor is pretty much dependent on the current rather than the power, and the current at low speeds and high torque can be high. If you are able to set up a current limit in the inverter, it should be set to the same or a little less than the motor maximum rating.

John