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Anonymous Poster

Brush Lifters

09/28/2010 10:36 AM

What are they – why they used
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#1

Re: Brush lifters

09/28/2010 10:39 AM
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JohnDG
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#2

Re: Brush lifters

09/28/2010 10:41 AM

How about some context?

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Doorman
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#3

Re: Brush lifters

09/28/2010 10:47 AM

Rule #75: I will guess

Carpet Pile Brush Lifter? Like this?

Used to dress up carpeting pile, for better cleaning and appearance.

Other than that, I have no guess what you are after.

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TonyS
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#4

Re: Brush Lifters

09/28/2010 11:11 AM

At a guess it's a slip ring motor?

Now I've only ever seen one of these in 35 years in the business and that had been disabled after it wrecked the brush gear.

The motor starts with the brushes in contact with the rings. Once full speed is reached and the resistance is shorted out a handle on the brush gear housing is operated. First a ring is slid in towards the slip rings were it shorts a set of three contacts that are connected to the rings. It's second operation lifts the brushes away from the rings to stop any wear.

From what I've been told they were more trouble that they were worth.

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JRaef
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#5
In reply to #4

Re: Brush Lifters

09/28/2010 2:14 PM

Those are not exactly what we typically refer to as "slip ring" motors, they aren't really slip rings. The term for the motor is "Repulsion Start / Induction Run", sometimes erroneously just shorted to Repulsion Motor. The brushes are in contact with and shorting the rotor for starting, making it more like a Universal motor having a DC armature that provides higher starting torque. Then a centrifugal "brush lifter" disconnects them at speed so the motor can run more efficiently as a Squirrel Cage Induction Motor. it's a really old technology that has for the most part been displaced by Capacitor Start motors.

Wiki

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TonyS
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#6

Re: Brush Lifters

09/28/2010 4:16 PM

The one motor I worked on fitted with brush lifters was aprox 60/75HP and was defiantly 550V wound rotor three-phase slip ring. It drove an impact breaker in a calcium oxide plant.

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#7
In reply to #6

Re: Brush Lifters

09/28/2010 4:34 PM

Huh... why would you lift the brushes on a WR motor?

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TonyS
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#8

Re: Brush Lifters

09/28/2010 5:23 PM

Defiantly should have read definitely Ooopps

A shorting ring took the load off the bushes which could then be lifted to save wear during a long run. The plant the motor I worked on had been built in 1935. There were many weird and wonderful bits of kit. If I can find it I've got a Brook Crompton handbook that was issued to all industrial apprentices in the 60's & 70's which shows an illustration of one.

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#9
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Re: Brush Lifters

09/28/2010 6:20 PM

That makes sense now. I have never actually seen a shorting ring on the rotor, they always do that outside now, but I had heard they used to do it that way. Makes sense actually, it's always better to short the rotor at the rotor, but lifting the brushes to save wear and tear is brilliant!

Lots of moving parts though...

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TonyS
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#10
In reply to #9

Re: Brush Lifters

09/29/2010 12:27 AM

The one I worked on had been disabled due to it ripping the brush-gear apart a some time.

More trouble than they were worth.

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