Electronic – Induction Motor Starting Problems

induction motormotor

First off I'll start by saying that I have almost no experience of single phase induction motors but I do have a reasonable knowledge of electrical & electronic stuff.

My neighbour asked me to have a look at a two post lift he has, which was not running properly/at all. First off, I found a few connections which were loose and once corrected the motor tried to run – so it seems to have cured the intermittent problem. The motor is configured to run in either direction through a couple of contactors.

The real issue is that it does not seem to want to start correctly all of the time. Sometimes you can get it to run well, but most of the time it either does not move at all, or runs very slowly and makes that horrible growling noise of a stalled AC motor.

I have checked both capacitors with a DVM and they both measure within the value marked on the side of them. He tells me the motor was sent for a checkup a while back and came back with a clean bill of health, but annoyingly he couldn't find the paperwork that he got for it and the motor has no identification on the outside. At a guess it's a 3-4kW motor. I'm in the UK so we use 240V 50Hz.

There is a starting relay, Klixon 2CR3-285. The datasheet (https://www.muekra.de/downloadfile/download/aitfile/aitfile_id/671/) for this suggests that it does not pull in the contact until a fairly high current and will drop out at 26A min. I am wondering if it may be that this is rated too high and a lower value or alternative part should be used. I wonder if depending on the rotor position sometimes there is enough current to pull the relay in, but at other times there is not. I guess I could measure the approximate resistance of the winding and use ohms to guess the operating current, but all these calcs go out the window during inrush and I don't have an LCR meter.

I've had a Google and can't seem to easily find these relays in the UK. There is some kind of overload protection relay inside the controller which is set to just above 16A continuous, with about double that peak (I'm guessing).

I think the terminals in the box are just so that you have something to screw down to. I don't think they are connected to the motor as there are 4 other wires coming from the bottom of the terminal box, but I'm not certain of this…

Here are a few pictures, not very good I'm afraid I didnt think at the time..:

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Any help is greatly appreciated.

Best Answer

Because your documentation is not detailed enough, all I can do is give you general information.
Most large power motors have two rotor windings. One is the "starting" and the other is the "running" winding. It appears that your motor's starting winding is not being "activated." Based on your description, the only thing that could be causing the problem is the starting relay.