Universal motor manufacture

In summary, this food mixer is a sentimental item that is barely used and has a bad connection in the motor. The motor arcs and gets very hot. The issue can be fixed with switch cleaner.
  • #1
Guineafowl
752
358
I’ve been given a food mixer to repair - more sentimental value than monetary. It’s barely been used, if at all - the brushes still have their bedding-in ribs. It would only run if I gave it a spin, but this was just bad contact between brushes and commutator. Solved with switch cleaner. When running, it arcs badly and gets hot.

The motor is a series-wound, brushed universal type, and is very badly built. There is no epoxy to stabilise the windings as they leave the commutator, and one of the segments has been left unconnected. The windings have been looped under the tab for each commutator segment, and the tab has been pressed down over it.

The ‘good’ segments have a resistance of about 1.8 ohm between each pair, but many are much higher, and the reading changes if I press down the tab.

When such a motor is made, how is good contact normally made between the winding wire and the commutator tab? Is pressure sufficient to displace the varnish, or are they normally heat-staked or spot welded? Solder?
 
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  • #2
Based on what you are saying its a bad connection, as to how its made, all of the methods you mentioned are probably used, except heat stake, to me at least that's deforming plastic to hold something (eg PCB).

Its likely one of those things where you won't know until you carefully try to dismantle and see, risking off course not being able to get it back together. If you're lucky its a dry solder joint... Mind you its not working right now anyway so what's the worst that can happen?

Do you have a picture of the offending commutator?
 
  • #3
essenmein said:
Based on what you are saying its a bad connection, as to how its made, all of the methods you mentioned are probably used, except heat stake, to me at least that's deforming plastic to hold something (eg PCB).

I was wondering if a higher temperature version of that plastic technique is used to melt the varnish at the point of contact.

essenmein said:
Its likely one of those things where you won't know until you carefully try to dismantle and see, risking off course not being able to get it back together. If you're lucky its a dry solder joint... Mind you its not working right now anyway so what's the worst that can happen?

Several adjacent segments have a resistance of 1.88 ohm, +- 10%. Others have anything from 11 to 300 ohm. It’s a very crappy motor. Normally, I test a commutator by seeing if adjacent, then opposite segments have consistent resistance. Here, I’m not sure - the arcing suggests shorted windings, but maybe the heat is from the high resistance connections at the commutator tabs.

essenmein said:
Do you have a picture of the offending commutator?

No, sorry. The mixer is back together now - it’s beyond economical repair (manufacturer is based in a small village in India).
 

1. What is a universal motor?

A universal motor is a type of electric motor that can run on either AC or DC power. It is commonly used in household appliances such as vacuum cleaners, blenders, and power tools.

2. How is a universal motor manufactured?

A universal motor is typically manufactured using a combination of stamped and wound components. The stator, rotor, and commutator are all made from laminated steel sheets, while the windings are made from copper wire.

3. What are the advantages of a universal motor?

Universal motors have a high power-to-weight ratio and are able to operate at high speeds, making them ideal for use in small, portable appliances. They are also relatively inexpensive to manufacture.

4. What are the main differences between a universal motor and other types of motors?

Unlike other types of motors, a universal motor can run on both AC and DC power. It also has a higher speed range and can provide high starting torque, making it suitable for applications where high speed and power are required.

5. What are the common uses of universal motors?

Universal motors are commonly used in household appliances such as blenders, food processors, and vacuum cleaners. They are also used in power tools, hair dryers, and other portable electronic devices.

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