Electric motor design question?

[Cheddar]

Hello,

When looking at the carbon brushes on our washer/dryer motor I noticed that the brushes are not perpendicular to the commutator, makes sense I thought, the brushes are angled away from the rotation of the commutator, i.e. the brush trails across the commutator thus reducing wear.

However I then realised that the opposite is the case and the brushes are angled TOWARDS the rotation of the commutator which I would have thought would promote wear.

Any ideas why it is designed this way?

Regards.

[Martin]

Re: Electric motor design question?

Cheddar wrote:Any ideas why it is designed this way?

It’s called ‘leading edge and trailing edge’. At any one time with a fully reversing motor it has to be like that to ensure sufficient drive torque. With smaller single direction brush motors the brushes generally are fully right-angled to the commutator.

HTH? 😀

[Cheddar]

Re: Electric motor design question?

Martin wrote:

It’s called ‘leading edge and trailing edge’. At any one time with a fully reversing motor it has to be like that to ensure sufficient drive torque.

Hi,

That is clear however both brushes are angled towards the rotation of the commutator (leading) so when the motor reverses both would be trailing, surely one angled towards the rotation and one against would be better so it is the same (one leading, one trailing) whichever way the motor rotates?

Many thanks.

[Martin]

Re: Electric motor design question?

Do what? 😕

What machine? What motor? Can you post a photo for me to see? Never seen the like before if your description is correct? 😕

[Cheddar]

Re: Electric motor design question?

Hi,

A CESET motor in an Ariston:

I have found this link:

http://www.emersonappliance.eu/washing_ … motors.htm

It is as per the top picture exactly, as you can see from the position of the two brushes, if the motor rotates one way both brushes will lead and if it rotates the other way both will trail.

Any thoughts?

Thanks.

[Martin]

Re: Electric motor design question?

Cheddar wrote:Any thoughts?

Yes….Your description was incorrect, take a close look next time at the brushes and you will see (and I refer you to my first post here) one leading one trailing whilst rotating clockwise, one leading and one trailing anti-clock.

You’re not convinced are you?….trust me & I can still teach my granny how to suck eggs, and she hates eggs. :rotl:

[Cheddar]

Re: Electric motor design question?

Martin wrote:

Yes….Your description was incorrect, take a close look next time at the brushes and you will see (and I refer you to my first post here) one leading one trailing whilst rotating clockwise, one leading and one trailing anti-clock.

You’re not convinced are you

Yes, I am not convinced because my description was correct. Your input is appreciated though 🙂

Look again at the top picture in my link, at the position of the two brushes, it is as I said – if the motor rotates one way both brushes lead and if it rotates the other way both trail.

One explanation that has been suggested to me that the motor will only run at high speed in one direction.

Many thanks.

[Martin]

Re: Electric motor design question?

Cheddar wrote:One explanation that has been suggested to me that the motor will only run at high speed in one direction.

Ah…that’s why I keep going round in circles on this issue then? 8) 😀

But seriously, of course it will only spin at high speed in one direction only.:wink:

Your challenge now (should you wish to accept it though?) is, what direction does your CESET motor spin at full speed then? Clockwise? or Anti-clockwise?Does it spin OK?

[kwatt]

Re: Electric motor design question?

The offset of carbons can be seen clearer here

They are offset like this in almost all cases, some more pronounced than others.

K.

[Cheddar]

Re: Electric motor design question?

Martin wrote:
Your challenge now (should you wish to accept it though?) is, what direction does your CESET motor spin at full speed then? Clockwise? or Anti-clockwise?Does it spin OK?

Challenge accepted 8)

It spins anticlockwise from the commutator end, i.e. with the brushes leading, which I would have thought would promote wear – hence my original question – spun full circle 😉 .

Thanks

[Cheddar]

Re: Electric motor design question?

kwatt wrote:They are offset like this in almost all cases, some more pronounced than others.

K.

Thanks, strange that they trail when motor rotates one way and lead when it rotates the other way, perhaps it is the high speed mode that dictates though why should they lead when in high speed mode?

Regards.

[Martin]

Re: Electric motor design question?

Cheddar wrote:which I would have thought would promote wear – hence my original question

You are quite correct in that assumption in that wear is very much subjected to the leading edge brush only. The very first of the 2 to fail is always the leading edge brush – fact. 😉

Promoting wear? Indeed so too, but it wouldn’t work any other way if truth be known. 8)

…or to confuse the whole thread even more here is a definition of friction…..”A force on objects or substances in contact with each other that resists motion of the objects or substances relative to each other.”

Hence promoting wear but hey….at least we get rotation and compromise has to be made somewhere to achieve it.

I’m sure you will agree? 😀

[Cheddar]

Re: Electric motor design question?

Martin wrote:You are quite correct in that assumption in that wear is very much subjected to the leading edge brush only. The very first of the 2 to fail is always the leading edge brush – fact.

“The leading edge brush” 😕 they are both leading, er, or both trailing, depending on which way it is rotating?

Regards.

[Martin]

Re: Electric motor design question?

Right again!

But somehow I feel I’m going round in circles here?………..you have a good day anyway – bye! 😀

Cheese and biscuits for tea now……bye :rotl:

[iadom]

Re: Electric motor design question?

AFAIK, one of the reasons for ‘reaction’ brush gear is to eliminate the side to side movement, however small that you will get with brushes set at right angles. This helps to keep the face of the brush in closer contact with the comm on high speed reversing motors.

No doubt Bob Okines could give a more informed opinion.

Jim.

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