Carbon Brush Modification - thoughts.....

[dishman]

Question - I have purchased some replacement carbon brushes for my tumble dryer.

Not for the motor, but for part of the automatic moisture detection system on a Miele.

The carbon brushes are attached to an armature which runs along tracks on the exterior of the drum.

Apparently a small current is passed through the drum and when there is a change in the current, due to the evaporation of water, it knows everything is dry. The current passes through the carbon brushes.

The issue is that these carbon brushes do not seem to have much longevity. Due to the shape and curvature of the drum, they are totally worn when only 1/3 used.

I have bought replacements. But due to the odd shape, they cost £22 a pop, which is extortionate for carbon brushes.

So, my working theory is to buy a more standard carbon brush (long thin rectangular shape) cut out a small slot, so that these carbon brushes can slot in. It then gives them a bit of Carbon brush shoe.

My question is, 1) will this work 2) will soldering one carbon brush to another work, or will solder not take to a carbon surface.

This is the shape of the current brushes:


As soon as they have worn to just under the stamped number, they are pretty much useless as they wear at an angle.

The armature:



Then use something generic but slim enough to fit in the tracks - cut a groove out.
Then maybe soldier them together.



This would cut the brush replacement from £20 a pop every few years to £2.

Thoughts?

 

[big-all]

is there no way to reduce friction a bit not so much to break the contact but enough stop excesive wear
is the commutator or rubbing surface fully smooth and clean as any pitting can cause excessive wear

 

[dishman]

No, it just slides along those tracks you can see in picture two - they are just smooth metal tracks. The contact force is determined my the armature which has a simple spring arm, like that of a windscreen.

Here is another angle:

 

[big-all]

lots off dips and bumps on the track by the looks off it
i suppose it needs an strong spring to react quickly to the moving drum
when you pull the arm back does it get noticabley tighter
as in iff you increase the working thickness off the brushes could it cause excessive pressure that could wear out the track or indeed cause the arm to fail ??

 

[dishman]

The tracks are pretty smooth, it is just has a lot of carbon deposit dirt. Yes the drum will oscillate slightly as it rotates which will mean the spring had to compensate.

But, you made me think of something.

The wear on these things should not be at an angle. As carbon brushes pivot about a fixed point, they should always make contact with the drum at a 90 degree angle along the bottom length.

I wonder if the carbon deposit has slowly made them stiff and then stuck at a certain angle. This may have contributed to uneven wear at an angle.

 

[big-all]

you will get drag that will pull the front end down and lift the back
maybe turn them round after a year and even out the wear
edit
that should off course be lift the front and drop the back

 

[dishman]

Yeh, they do also have a sponge washer sandwiching them on the retaining bar. This does not exactly aid free movement either.

I also wonder how much the drum reverses, I would have thought this would even out the wear itself....but apparently not.

This is the new one compared to the worn one



I wonder if an alternative washer will help it angle more freely.

 

[Jackrae]

Clearly you have a problem yet to be identified. Either the drum isn't reversing or the brush is not free to swing

 

[dishman]

Yes, the angle is an odd one I think it is probably the latter.....I will have to test it to see the reversing action.

This one seems to have had even wear. Even without the odd wear angle there is not much clearance, so it only has to wear a small amount to begin catching.

 

[ban-all-sheds]

Bizarre.

We've got a Miele TD, with auto-dryness sensing. Had it for decades and never had to replace anything.

 

[dishman]

Bizarre.

We've got a Miele TD, with auto-dryness sensing. Had it for decades and never had to replace anything.

Interesting, I got given this by a family member, they did not look after it (cleaning mostly) so I have refurbished it as it is not that old. It looks brand new now.

My view is that the method of sensing dryness in this is very over-engineered. My parents have an old hoover that has been going for 30 years and although it is not in the best condition cosmetically, it has never needed a replacement part in that time. That too seems to have an auto-sense functionality (although everything has to get bone dry for it to work, so it has rarely been triggered before the timer).

This Miele by comparison seems overly complicated for little gain.

Convenience over functionality. Which I guess is a common theme for modern white goods.

However, it seems they have been using this method to sense dryness via an armature and replaceable brushes for a long time. So, I am curious how yours operates. Have you ever lifted the lid to see if it uses a similar solution?

 

[ban-all-sheds]

Nope - the only "maintenance" we ever do is to clean the fluff filter. And I'm not exaggerating about "decades" - we've had it 20-30 years. I've never run any experiments to see how dry things come out depending on the dryness setting chosen.

I'd not be surprised to learn that closer control over dryness at the expense of reliability was done to squeeze an extra '+' onto the efficiency rating.

 

[dishman]

This is their video showing how the system is intended to work. Not that it's hard to work out for most people...

They don't seem to mention the bit about replacing the carbon brushes. When the carbon brushes wear too low, it starts an awful knocking as per the previous video. I bet a lot of people think the bearings have gone and bin them.

Do you have the model number of your dryer @ban-all-sheds , I am curious as to how the design has changed.

Miele always struck me as one of the few companies that preferred robustness over gimmicks. So I wonder how the implementation of the auto-sense has changed.

 

[ban-all-sheds]

Novotronic T640

 

[dishman]

Thanks, I can't find specifics about that model, but I did find this about an even older model, a T366 from the early 80's. And while the bracket arrangement is different, it still uses the same method of sensing. It looks a bit more robust though....

Skip to the 15:00min mark...

So it seems they have indeed been using this method for a very long time. Maybe the wearing of the brushes on older models give no audible indication something needs replacing.

Maybe when you have a chance or the inclination you may want to pop the lid and see for curiosity. But, if it works....