Motor Wiring

[HarryJ]

Hi
I have an older motor which I am trying to re connect to the mains electricity.

The motor is a Crompton Parkinson
0.5HP
3.8A
Single Phase
220/240 Volt
50Hz
1425 RPM
and its rating is continuous.

-I'm pretty sure that is all that was on the motor plate

(Some of this information will, I'm sure not be necessarily relevant as being I gave the current and also the voltage, the power can be calculated)

From what I can remember and see from the image I took, the red and black wires go back behind the brown mounting plate.

The labelling on the brown plate, which I do not understand, is as follows; (working down) K,Z,AZ,A,T (there is also a S hidden behind the earth wire but as far as I can see, it doesn't do anything -in a similar sort of way as the K at the top doesn't seem to do anything either)
[for reassurance of my descriptive skills, the Z is at the top and has a yellow connection wire, the AZ has the blue and red wires, A has the Black and Brown wires, and T has the blue wire at the bottom of the image]

-->Just realised the image is orientated landscape which means the left is supposed to be the top

When I plugged the motor in like this (just a plug on the end of the cable as I was only testing the motor for now), the motor buzzed for a few seconds like a motor does when it can't turn and then the fuse blew. All rotating parts connected to the motor are free running and can be turned by hand (am I possibly connected to the run windings only or something?)

How do I correct this problem?
How would I connect the wiring so that the a reversing switch can be used also, or is that a separate affair all together and doesn't rely on the initial motor set up.

Hope this is all that is required for this problem as I have included everything I can think to.

Any help would be much appreciated
Thanks,
Harry.

 

[MMUK]

First thing that immediately springs to mind is that your live and neutral are on the run coil.

Connect your brown wire (live) from the power cable to terminal AZ (with the thick red wire and the smaller blue wire) and the blue wire (neutral) to terminal A.

The Z and T terminals are the start coil. Connect the Z to the neutral and T to live. The start coil has an internal switch that disconnects this coil from the mains once operating speed is reached.

If that doesn't make sense, here's a quick sketch

This is for forward running only, I'll get back to you with reverse running

One thing to bear in mind is that start up current could be up to 3x that of normal running load.

I am a little confused at the data on your plate though. A 0.5HP motor is only 375w so should only be drawing about 1.6A continuous.


I assume this is from an old Myford lathe?

 

[MMUK]

OK, reverse running means you will need an external switch to reverse polarity. This switch will need to be double pole with an "OFF" position in the middle.

Note: Where the wires cross over in the drawing they are not joined

 

[HarryJ]

I thought it might be on the run coil, as although I can't say I know too much about electric motors, I knew the start coils were different and required a higher amperage than the run coils.

Thank you very much for the information, I'll try it at the weekend as I have no time during the week. I'll let you know how I get on.

As far as I know, the data I gave you about the motor is all correct, however according to my calculations, the motor would be about a 912W motor with a voltage of 240 and current of 3.8A, but I don't really know how this works out with HP generally...

Yes, this motor is from an old Myford lathe, but how did you know?

I've got a Dewhurst Switch coming for reversing the polarity.

Thanks again,
Harry

 

[MMUK]

I recognised the connection layout as typical of a Myford motor.

As for HP, 912w would be approximately 1.2HP which is not a common size so I would make an educated guess that the 3.8A stated is the start coil current. The run coil should draw about 1.6A for a 0.5HP motor.

 

[HarryJ]

I've been to have another look at the motor today and the suggested wiring has worked, however now the fuse blows after a very short time of going.

I've been using a 5A fuse because that seemed the most appropriate from the rating given (3.8A) on the plate.

I'm not sure however, if the fuse blowing is because the start coil is in fact drawing 3x that of the stated amperage, as you said it could do, or if its because of another fault which I do not know about.

Any comments as to where to go now?

Thanks,
Harry

 

[MMUK]

try a 13A fuse and plug it into an RCD socket if you can. If the RCD trips, then you have a fault. I would suspect though that the start up current may well be in the region of 8-10A.

 

[HarryJ]

I tried a 13A fuse using a 'portable' RCD and the motor did run, but now when running, it was shaking and something began to burn, but the RCD did not trip... does this mean it was burning off something in the motor, or is this an electrical problem and my RCD isn't working maybe?!

I don't know how noisy the motor is supposed to be, but it wasn't quiet when it was running.

I'll try another RCD tomorrow but until then, any more suggestions?

Thanks,
Harry

 

[MMUK]

If it's been stood for a while you may get a bit of smell from dust burning off but that shouldn't last for too long. The motor shaking may mean a slight imbalance or it may just be concentric force as it's not bolted down.

If you have a multimeter, check the winding resistance (ohms) with the mains leads disconnected and post the results up. You'll need to test between A & AZ and T & Z. You should get two slightly different readings as the coils are different ratings.

 

[MMUK]

Just checked and the T-Z winding should read around 10 ohms and the A-AZ winding around 7 ohms.

If you're really stuck and don't mind paying postage, I can give it a strip down and refurb for you.

 

[HarryJ]

I tried the motor again to today, and although the shaking seems less, the burning seems more...

I also measured the resistance between A & AZ and T & Z and got a reading of 0 ohms for both, which I assume may be a slight problem...

 

[MMUK]

I tried the motor again to today, and although the shaking seems less, the burning seems more...

I also measured the resistance between A & AZ and T & Z and got a reading of 0 ohms for both, which I assume may be a slight problem...

Granny suck eggs and all that but is your multimeter auto ranging or do you have to select a range manually? For manual selection it will normally be the 0-200 ohm range you need. Otherwise you'll end up with a zero reading Either that or your meter battery could need replacing. I doubt the motor would run if the coils were 0 ohms.

 

[HarryJ]

My multimeter is a manual select, and I tried the lowest available (admitidely, it is 20K)

I just re-tried, measuring the resistance using a setting which it says is meant for diodes, but its on the same dial as the resistance... but this time, I read 4 ohms from both, so looks like it may have been my poor measuring but I'll call it a mistake with the multimeter
I think I'll get a new multimeter though...

Still, 4 ohms for both when you say one of them should be about 10 doesn't seem right