Happy Harry
Member
I have a 240v single phase motor which seems to have seriously lost power. It is a budget motor fitted to a cement mixer so it is probably 4 pole about 375watt.
I have dismantled it and can see no obvious signs of damage or overheating so I made a few measurements with my multimeter and put them in a little sketch. The first problem is that I cannot find a way of downloading the sketch (jpeg file) onto this page so I can only describe what I have done and ask if you can convert my description into a picture for yourself so that you can understand what I am talking about.
The picture is an illustration of the arrangement in the terminal box and is as follows:
Draw 4 terminals at the corners of a square and since there is no lettering against these terminals label them A and B on the top left and top right and C and D on the bottom left and bottom right.
Terminals A and C are connected to the windings at the left hand side of the motor and terminals B and D are connected at the right hand side of the motor to the windings.
There is a 12uF capacitor between terminals A and C.
There is a link between terminals B and D.
The mains supply is connected to terminals A and D.
The capacitor was replaced some years ago and the mixer has been seldom used since. I cannot remember what prompted me to use a 12uF capacitor so I hope that I chose an appropriate value for this size of motor. Anyway, I'm certain that the motor was running at full power after changing the capacitor.
Now for the measurements:
With the capacitor disconnected but the link still connected.
A - B 9.8 ohms
A - C 31.6 ohms
B - C 21.9 ohms
With both capacitor and link disconnected:
A - D 9.8 ohms
B - C 22.0 ohms, also
A - B 66 Megohms
A - C 70 Megohms
C - D 68 Megohms
B - D 70 Megohms
All measurements were made with a digital multimeter and insulation resistance of windings to case was outside the top 200 Megohm range. Sorry , no megger available.
Has anyone got any ideas what is at fault to cause this loss of power and is it repairable? Apart from the expense for a seldom used piece of equipment it would be nice if instead of purchasing a new motor I could keep the old one and avoid having to fabricate a different mounting and belt adjustment arrangement.
I have dismantled it and can see no obvious signs of damage or overheating so I made a few measurements with my multimeter and put them in a little sketch. The first problem is that I cannot find a way of downloading the sketch (jpeg file) onto this page so I can only describe what I have done and ask if you can convert my description into a picture for yourself so that you can understand what I am talking about.
The picture is an illustration of the arrangement in the terminal box and is as follows:
Draw 4 terminals at the corners of a square and since there is no lettering against these terminals label them A and B on the top left and top right and C and D on the bottom left and bottom right.
Terminals A and C are connected to the windings at the left hand side of the motor and terminals B and D are connected at the right hand side of the motor to the windings.
There is a 12uF capacitor between terminals A and C.
There is a link between terminals B and D.
The mains supply is connected to terminals A and D.
The capacitor was replaced some years ago and the mixer has been seldom used since. I cannot remember what prompted me to use a 12uF capacitor so I hope that I chose an appropriate value for this size of motor. Anyway, I'm certain that the motor was running at full power after changing the capacitor.
Now for the measurements:
With the capacitor disconnected but the link still connected.
A - B 9.8 ohms
A - C 31.6 ohms
B - C 21.9 ohms
With both capacitor and link disconnected:
A - D 9.8 ohms
B - C 22.0 ohms, also
A - B 66 Megohms
A - C 70 Megohms
C - D 68 Megohms
B - D 70 Megohms
All measurements were made with a digital multimeter and insulation resistance of windings to case was outside the top 200 Megohm range. Sorry , no megger available.
Has anyone got any ideas what is at fault to cause this loss of power and is it repairable? Apart from the expense for a seldom used piece of equipment it would be nice if instead of purchasing a new motor I could keep the old one and avoid having to fabricate a different mounting and belt adjustment arrangement.