Re: Shunt field motors

[Victor Tikhonov <vtikhono@lsil.com>]

It does, very clear. Thank you for ascii effort.
I failed to realize that any coil the brushes are not on at
the moment will have voltage across them. So only moving brush plate
can resolve this then (unless sep-ex motor used).

I better go back to AC stuff I know more about...

Victor

Lee Hart wrote:
> 
> Victor Tikhonov wrote:
> > The idea was to have extra set of identical thickness brushes,
> > so they still short two bars.
> >
> > Imagine commutator bars twice as *long* so another set of identical
> > brushes is there along the shaft, one set behind the other.
> > And the second set can be rotated to whatever angle needed.
> 
> I think I understand what you are suggesting, but still think int won't
> work.
> 
> Imagine "unrolling" a 12-bar commutator, so the bars are flat across the
> width of this page. At this particular moment, the brushes are shorting
> coil 1 and coil 7. But that's OK because these coils are at right angles
> to the magnetic field, and so have zero voltage across them.
> 
>                magnetic field                      magnetic field
>     +               _| |_               -                / \
>   __|__             \ N /             __|__             / S \
>  |brush|             \ /  commutator |brush|           /_   _\
>  |_____|              V      bars    |_____|             | |
>  _     _     _     _     _    \_     _     _     _     _     _     _
> |_|   |_|   |_|   |_|   |_|   |_|   |_|   |_|   |_|   |_|   |_|   |_|
>  |     |     |     |     |     |     |     |     |     |     |     |
> _|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
>     1     2     3     4     5     6     7     8     9    10    11    12
>     0v   10v   17v   20v   17v   10v    0v  -10v  -17v  -20v  -17v  -10v
>                     _| |_                                / \
>                     \ S /                               / N \
>                      \ /                               /_   _\
>                       V                                  | |
> 
> If you add a second pair of brushes at any position except coil 1 and 7,
> then they short a coil that has voltage across it. Does that help?
> --
> Lee A. Hart                Ring the bells that still can ring
> 814 8th Ave. N.            Forget your perfect offering
> Sartell, MN 56377 USA      There is a crack in everything
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