# Very premature brush wear! Please help :(



## major (Apr 4, 2008)

It is good you inspected and found this as if left unattended it would have caused a lot worse damage. I don't know the cause for sure, but first suspect would be the replacement brushes themselves. Good quality? Proper grade? I'd check back with the place that sold you the brushes. I think they should have been H-100 grade.


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## favguy (May 2, 2008)

Hi Major,

They struggled to find the size, so I suspect they are the only option they had. I'll probably have to buy a set for a warp 9 and machine them down to fit in order to get an EV suitable grade (assuming that's the problem!)

Any thoughts on why there is such a huge difference in wear on the rear set though?


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## major (Apr 4, 2008)

favguy said:


> Hi Major,
> 
> They struggled to find the size, so I suspect they are the only option they had. I'll probably have to buy a set for a warp 9 and machine them down to fit in order to get an EV suitable grade (assuming that's the problem!)
> 
> Any thoughts on why there is such a huge difference in wear on the rear set though?


I see this to a lesser degree occasionally. Not sure why. Mechanical difference on the comm? Surface finish difference? High bar? High mica? Or electrical? Difference in path resistance? Circulating currents across brush face (split brushes might help)? Too much advance (12º sounds like a lot)? Proper break-in? Contaminate? Any silicone in there?


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## favguy (May 2, 2008)

No silicon and the comm. seems good, no high spots. I suppose the rear brushes come off the nearby bus bar first, so maybe get more current? I wouldn't really be too worried about them wearing a bit faster if it was after 50K or so! 

12 degree advance was to allow me to run at up to 156v later when I upgrade the pack, didn't think it would harm at 120v. Can brush advance cause premature brush wear then? (All Netgains run at 12 degrees after all).

Do you happen to know if you can get the split brushes made to size? 

Thanks for the help.


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## dragonsgate (May 19, 2012)

Can you get a picture of the commutater?


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## kennybobby (Aug 10, 2012)

If you have some calipers with inside jaws you might measure the aperature gap at the front edge and rear. Then measure brush thickness and compare to the gap to see if the rear brush is held tighter and not so free to slide.

Are the springs wound with the same number of turns--a tighter spring might cause higher brush wear.


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## favguy (May 2, 2008)

Hi,

It's difficult to get a picture of the comm. in situ, but It looks and feels OK.

The brushes are all equally free to slide up and down, nothing is tight or sticking.

I have got a reference from the brushes in question, LFC3, will this be the grade? and if so, does anybody know if it's correct for EV use?

Edit: Found the following online regarding LFC brush grades,

*LFC 
SOFT GRAPHITE BRUSHES​*The base constituent is purified natural graphite or previously ground artificial graphite, then mixed with other
constituents in well defined quantities, agglomerated with appropriate binders and fired in order to coke the
binder.​*Main character​*Soft, plastic brushes having very good resistance to shock and mechanical vibration. Generally they have
good cleaning properties.​*Principal applications​*Steel and stainless steel rings for high speed synchronous machines.​*Limit of application​*Brush current density:10 to 13 A/cm​​​​​​​​​2 (maximum).
Admissible peripheral speed: 65 to 90 m/s (even to 100 m/s).


​


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## favguy (May 2, 2008)

OK, I think the brushes are the culprit here, after further reading, it would appear this grade of brush isn't suitable for DC traction applications. It's too soft, supposed to run at a lower spring tension than we have on our DC motors and can't handle the current levels we use either . It's a good job I'm light footed, or I'd probably have blown them up, on closer inspection there is actually heat damage to the brush I've looked at where the wires are pressed in).

It seems my brush supplier found me brushes that physically fitted with no regard to the composition or intended use!! Bad show


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## major (Apr 4, 2008)

What you want is Electrographitic grade H100 which may have been superseded by T300. Or just insist on the same as used in the WarP9. But a soft graphite for steel slip ring applications would be totally wrong  

Again, good catch  Letting those go to the point where they lost contact from wearing to short would have caused major damage to the comm.


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## favguy (May 2, 2008)

Yeah, I should be really annoyed with the supplier, but I'm just pleased it's nothing more serious and I spotted it in time. Good job I didn't get round to hiding it away under a cover band sooner or I might have known nothing until the motor was trashed!

Thanks again for your input


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