brushes

[billi]

Hi

one of my generator s  eats  these brushes  ( are  they magnates ?) recently ,  they wear of very quick , is there a reason?

Where would i get  replacement , they are just rectangular black blocks with no wire ....similar to those  (but  without a wire )



Thanks  Billi

[Justme]

What is the condition of the contacts that they touch?


I would guess that either they are rough (poss been refaced using rough sand paper) or that one segment is raised above all the rest & is eating them away.

[knighty]

how hard do you work it ?

I'm pretty sure they're supposed to get hot and work up a pocket of gas between themselves and the rotor, so they float there not actually in contact with the rotor but so close they still conduct ?

(or something like that)

so if it doesn't work hard enough, it won;t build up the pocket of gas and will rub on the rotor ?

[eabadger]

Could be excessive sparking, run it in dark to check, yes normally comutator needs re cutting.
Or channel brush sits in is making brush not contact correctly, causing erosion through sparking.

steve

[billi]

Thanks 

True  i saw them sparking  today

Or channel brush sits in is making brush not contact correctly

Can you explain ? I thought the housing  of the brush  transfers  the power    But obviously there is another contact

So i should  have a closer look  inside  the brush  housing  and inspect  the connections ?

[eabadger]

You are correct, if no wire to brush, housing transfers power, check housing is clean, tarnish free, and brush is correct size, not too loose, as this can also cause sprking, which creates heat and bad connection, which creates high resistance, which creates heat and high connections which creates ……….


steve

[Philip R]

Billi,
Normally the current is transferred to the brush via the copper braid(shunt). Other times it is transfereed to the brush via the brush box ( the brass rectangular tube the brush sits in. It depends on how the brush boxes are mounted as to whether they are isolated or floarting potential.

Your mentioned a raised segment (on the commutator) Has this machine beene overloaded or started in a stalled condition. This may have damaged the commutator. Has the commutator been skimmed down, were the insulation mica between the segments undercut  with a clean section of fine hacksaw blade? Otherwise this will lift the brush and make it spark.

With the machine shut down, are there any patterns on the commutator, burned segments, dodgy patina etc. Please enclose a photo of the comm if possible ( shutdown). Comm patterns are good diagnosis tools for other problems like winding faults, incorrect grade of brush, wrong current density, incorrect brush pressure etc.
PhilipR

[guydewdney]

clean commutator with fine file, preferably diamond. clear out gaps. check spring tension.

[johnrae]

Ideally the commutator should be a copper colour with maybe a hint of blueing.  If the segments are black and rough then they need skimming.  Files and/or emery paper will not give good results. 

Brush compounds come in many grades from extremely soft carbon to quite hard copper/bronze loaded compounds.  It could be that you are/have been using the incorrect grade of brush compound  -  you should try and find out what was specified by the genny manufacturer.  In all probability the commutator is damaged and requires reworking. 

If the insulation between segments is at the same level as the commutator segments then the brush pressure is being biased off due to the insulation and the insulation requires undercutting.  This can be done by a knowledgeable amatuer once you have stripped the rotor from the generator but you'd be better using a motor repair shop who could skim the commutator and undercut the inter-segment insulation.

Another source of weakness is the springs that press the brushes onto the commutator.  If they have become overheated (due to brush sparking) they will have lost their temper and gone "soft".  As a result the brush pressure will be too low causing the brushes to float and cause back contact with the commutator - resulting in increased sparking and wear.

As a previous entry said, a close-up photograph will help with a diagnosis.

[camillitech]

Are they actually the right material Billi, you've not been using brushes out of anything AC have you  I know I have in the past and whilst it's a great temporary fix they seldom last, being made of different stuff, or so I was told by one who knows 

Good luck, Paul

[guydewdney]

oh - and check the 'timing' - run the genny and slowly slide the commutator ring clockwise and then anticlockwise to the point of minimal sparks.

[billi]

Thanks  all

I have made  some photos  ( hope they are good enough )

It  seems to me that the commutator has no segments     as well i found this little piece  of copper  close to the bushes  , so perhaps one of them  has no connection to  power ......

There is  a lot of  sparking and generator works at the moment ,  but it occurs that he is stopping  producing AC  Volts  from time to time ...., especially  when  stopping him to refuel  and restart

Thanks Billi

[camillitech]

Ahh Billi, thought you were DC charging, those are AC slip rings and they are fecked  Try running the engine with a block of wood and some emery paper pushing up against them  Stands back  and awaits torrent of H&S abuse but it works for me 

Cheers, Paul

[eabadger]

realy neads a spell on the lathe, but block of wood and metal oxide wet and dry would be ok.
i thought you were dc charging also, i have moved to this and it seems good, variable dc output 0 to 40v 2.8kw.

[billi]

Thanks 

I had a lovely   2 kw  DC  diesel charger ,but engine problem  and much more prefer  DC charging


 and  this AC one is  a rented one  from a friend ,so  you are  telling me that i should grind them flat ?