--- "Bukosky, Allen" <
[email protected]> wrote:
> I have seen a patent where a second set of brushes
> sense the armature
> voltage and cause a small motor to rotate the
> brushes to minimize this
> voltage. As I remember, this was intended for
> railway motor use.
>
> Being no motor expert by far, I may be all wet, but
> this thread
> surprises me because, as I understand it, the need
> for brush advance is
> due to "armature reaction". This is where the
> magnetic field developed
> by the armature, which is normally perpendicular to
> the stator field,
> causes an effective shift in the stator field. This
> makes the "magnetic
> neutral" position of the brushes different than the
> "geometric neutral".
> I would expect this effect to be more at low
> rpm/high torque(high
> current and high fields) than at lower current and
> high RPM.
>
> Perhaps inductance, hysteresis and eddy currents are
> the dominat factors
> at high RPM and need the same sort of brush offset.
> Without further
> reflection, it would seem so since the main problem
> with lack of brush
> offset is at high RPM and high voltage.
>
> Allen
>
> -----Original Message-----
> From: David Wilker
> [mailto:
[email protected]]
> Sent: Tuesday, July 31, 2007 12:14 AM
> To:
[email protected]
> Cc: Jim Husted
> Subject: Re: Neutral Timing is Better for Commuters
>
> Dumb question time:
> Can you rig an advance mechanism that would
> retard/advance the brushes
> in relation to RPM and/or volts/amps?
>
>
> David C. Wilker Jr.
> USAF (RET)
>
> ---- Jim Husted <
[email protected]>
> wrote:
> Hey all
>
> I haven't had the time I've wanted to address my
> thoughts toward brush timing like I'd like. Rather
> than watch another timing thread go by I thought I'd
> throw some thoughts at the group.
>
> Most DC motors are designed to be ran neutral and at
> a
> particular voltage, and in fact I spent most of my
> first 25 years building motors making sure they went
> out that way (older forklift motors had adjustable
> brush rings). It wasn't until I ran into Wayland
> that
> I had to start learning how and when to throw them
> out
> of wack, so to speak.
>
> So why advance the brushes when neutral is more eff?
>
>
> The first issue (for those that are new) is when the
> motor commutator arcs in what's been termed a
> flashover. This is caused by using higher voltages
> than the motor was intended for, which causes the
> field magnetics to shift which in turn causes the
> brushes to arc as they are no longer "in tune" with
> the fields. By advancing the brushes they line up
> with the fields when the motor is seeing that higher
> voltage and is running harder.
>
> By advancing the brushes you also see the motors
> power
> band shift further up the RPM scale. I've had
> reports
> of both "love" and "hate" increased advancement.
> The
> problem is "when to advance"?
>
> It was just last year that Pat Sweeney flashed his
> daily driver ADC motor, when he did it a second
> time,
> he sent it to me, where I found it running in
> neutral.
> After some cleanup and a few parts and setting it
> via
> the OEM advancement holes he's had no issues,
> besides
> a little loss on his takeoff 8^(
>
> Sometimes lifes a trade off, lose a little eff, or
> repair your motor a lot 8^P Now this doesn't apply
> to
> lower voltage EV's as much, but again that depends a
> lot on what motor one is using compared to what
> voltage it's being run at.
>
> I haven't heard from Bill as to when the brush shift
> was taking place on Killacycle, or how well he and
> scotty thought it was working but it was, I thought,
> a
> successful test of an on the fly brush timing shift.
>
> Being able to smoothly adjust the timing on DC
> motors
> as they run (just like an ICE) would help squeeze
> both
> better eff as well as performance.
>
> As I'm running short of time my advise to those in
> doubt is to advance the brushes and avoid themselves
> the costs of motor repairs. As Jeff's done a great
> write up on this MTC motor, I thought I'd post a bit
> for those not using the standard fare motors 8^)
>
> BTW Jeff, I know exactly what you meant with the MJU
> plates 8^) I'll see if I can dig some plates out
> (if
> I have any) and grab some pics of the different hole
> positions per your description.
>
> Anyway, yeah neutrals better for you dailies...
> right
> up to the point when you zorch your motor. IMO it's
> kind of like condom use, do you really want to
> chance
> "not" using it 8^) Of course the higher the juice
> flow the more that it's needed 8^o
>
> Hope this helps
> Had fun
> Jim Husted
> Hi-Torque Electric
>
>
>
>
>
>
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