Re: Info from Ah-ha! on BOSS's/Motors/HVdrivers

Hi,

The inductance is the same for parallel or half-winding. Look at it
this way; Does it matter if you use solid wire or stranded wire when
winding a coil? It doesn't.

The motor phase winding is bi-filar; two strands of wire are wound
simultaneously. For parallel operation the wires are connected to
form a 2 strand wire. For half-winding only one strand of wire is
used.

In either case the same current passes thru the same number of turns
of wire.

Your calculation of L is taken from series and parallel connected
resistors. It would be correct for 2 isolated inductors or chokes. It
does not apply to inductors sharing the same flux path because of
mutual coupling.

The correct way to look at two mutually coupled windings is to think
of them as a single coil of either N or 2N turns of wire. Inductance
is proportional to the square of the turns of wire. That is why a
series connection (2N) has 4 times the inductance of a half-winding
or parallel (N) connection.

Mariss

--- In CAD_CAM_EDM_DRO@y..., stratton@m... wrote:
> > There is less than a 2 to 3% "performance hit" running a motor in
> > half-winding instead of parallel. Let's take your 4.7A motor and
48V
> > power supply as an example. It is probably a 1.7 volt motor. If
it
> > were wired in parallel the coil resistance would be halved and it
> > would drop .85 volts instead. Since motor power is proportional
to
> > voltage, and this voltage subtracts from the power supply, what
you
> > have is:
> >
> > Half-winding: 46.30V ( 48 - 1.7 )
> > Parallel: 47.15V ( 48 - 0.85 )
> >
> > Taking the ratio of the two, the half-winding motor "sees" 98% of
the
> > voltage the parallel motor "sees", for a performance loss of 2%.
At
> > higher speeds where inductive reactance dominates and phase
currents
> > drop, this loss fades into insinificance ( << 1% ). Apart from I
> > squared R losses at low speeds, there is no advantage to parallel
> > connecting the motor.
> >
> > Mariss
>
> If each half of the winding has a given electrical inductance L,
then
> putting the two halves in parallel would give an inductance of L/2,
> and half the inductive reactance (or a quarter of that found in
series
> connection). In the regime where inductive reactance is dominant,
> won't this make a huge difference?
>
> Am I missing something? Does the fact that the two inductors are
> wound together mean they don't add the way isolated inductors would?
> (ie, one could argue two pieces of wire wound in parallel around the
> same core are really the same as one piece of bigger wire)
>
> Chris
>
> --
> Christopher C. Stratton, stratton@m...
> Instrument Maker, Horn Player & Engineer
> 22 Adrian Street, Somerville, MA 02143
> http://www.mdc.net/~stratton
> NEW PHONE NUMBER: (617) 628-1062 home, 253-2606 MIT