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I noticed the superior choice would be a carbon-based brush. However, would a pure copper brush be a bad choice?

I'm considering copper due to the lower resistance and higher current carrying capacity. I realized that the COE of friction for carbon brushes is indeed lower than copper, but is it manageable for motors or generators to use copper brushes for higher current capacity?

I assume the friction is too great, generating excessive heat and wear.

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    \$\begingroup\$ Welding and galling may be a problem... \$\endgroup\$ – Ecnerwal May 24 '16 at 14:08
  • \$\begingroup\$ Are carbon brushes more forgiving of the momentary short between commutator segments than a copper brush might be? \$\endgroup\$ – Transistor May 24 '16 at 17:12
  • \$\begingroup\$ COE coeffiecent of expansion? \$\endgroup\$ – Voltage Spike Jul 22 at 15:44
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Taken from wikipedia:

Early machines used brushes made from strands of copper wire to contact the surface of the commutator. However, these hard metal brushes tended to scratch and groove the smooth commutator segments, eventually requiring resurfacing of the commutator. As the copper brushes wore away, the dust and pieces of the brush could wedge between commutator segments, shorting them and reducing the efficiency of the device.

There is a related question here

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Under pressure and heat, copper smears. This will produce a layer of copper on the brushes which will short them out.

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  • \$\begingroup\$ One could use an extremely thin(0.001m) graphite sheet to coat the two surface for full conductivity and avoiding such problems? \$\endgroup\$ – Pupil May 25 '16 at 23:34

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