RE: surging, motor

["Naugler, Steve" <SNaugler Rodel com>]

Drag and braking of DC motors.
        A DC motor, permag or wound field, will have the same drag as an
induction motor of similar size except for brush friction IF the armature
windings are disconnected.
        A DC motor with a field, either a permag or a wound field with an
energized field, with the armature winding shorted will stop.  This is 
known
as dynamic braking.
        The mower motors when turned off have their armature connections
shorted together.  This is dynamic braking in action and is why they stop 
so
quickly.
        The traction motor, snow blower motor, and most other of the GE
accessory motors, when turned off coast slowwly to a stop.  In these cases
the armature connections are left floating when turned off.  This is a case
of (hopefully) low friction braking.  I am very careful when snowblowing
because the blower takes forever to stop and I worry about kids and pets.


-Steve Naugler
-e mail address:  snaugler rodel com

> ----------
> From:         Larry Elie[SMTP:lelie ford com]
> Sent:         Monday, January 04, 1999 12:51 PM
> To:   'Christopher Meier'; elec-trak cosmos5 phy tufts edu
> Subject:      RE: surging, motor
> 
> I have read all the replies to date on this thread, and they are all 
> good.  I'm very curious here...
> 
> ----------
> From:         Christopher Meier[SMTP:Christopher Meier cwix com]
> Sent:         Saturday, January 02, 1999 11:27 PM
> To:   elec-trak cosmos5 phy tufts edu
> Subject:      surging, motor
> 
> ;A little while back someone mentioned their unit was surging.
> ;Today, after putting on the chains, while plowing snow with
> ;a blade, my E16 started surging.  I believe that it is due to
> ;belt slip.  Both of my belts are old, hard, and a bit cracked.
> ;I plan to replace them both soon.  In fact, ASAP.  While
> ;trying to push snow up a small incline, the belts slipped
> ;while in any gear but low-low, and in fact slipped while in
> ;low low with a "full blade" of snow.  Since this is one of
> ;the main reasons I picked up the tractor, I plan to remedy
> ;this soon.
> 
> Did the belt squeel?  Mine did with 15" of snow yesterday.  It squeeled 
> more in reverse (?!?).  I don't know if it can slip without squeeling.  
> BTW, us E12 users only have one belt.
> 
> ;My E16 started something else new today.  Occasionally,
> ;when starting from a dead stop, the motor fails to go, even
> ;though all contactors clack and power is given to the motor.
> ;I reach down and turn the motor pulley just a bit by hand,
> ;and then it works fine.  I expect that I need to check the
> ;motor for servicing, but if I delay for a bit, am I likely to
> ;toast the motor?  I didn't want to have to pull it out the
> ;first week we get some major snow.
> 
> Are you sure ALL the contactors were closing?  Are you sure they 
> closed properly?  I have heard the 'clack' and not had them not close 
> (as proven by a clip-on Hall-effect current probe) to cary current.    
> I didn't damage the motor, because no current was going through the 
> motor.  BTW, I have not figured out what that was as of yet.  10 minutes 
> later, the machine worked fine.  Lift and lights worked all that time.
> The 
> contactors don't work if the voltage is very low, so I must have had 
> some 
> contact.  I plan to clean ALL the contactors in the spring, but this is 
> disquieting.  I did not try spinning the motor.  
> 
> ;Have any of you ever spun your motor with the belts off?
> ;Does it spin freely?  Mine stops rather quickly, there
> 
> Yes, I have.
> 
> ;appears to be quite a bit of drag on it.  I expect this
> ;also isn't normal, and I'd guess that the bearings need
> ;replacement?  How long should it freewheel when spun?
> ;I think there's a bit more noise then just brush noise as
> ;well.  My first close-interaction with a large dc motor.
> ;It doesn't make as much noise as my 20 year old power
> ;drill...
> 
> ;Chris
> ;E16 owner since July '98
> 
> I think mine free-wheels, but I haven't tried this in two years.  
> However, the mower blades on my old E12 have a 'electric-brake' 
> that shuts them down in about a second.  Since the E-12 is 
> a bit different than yours, it may be wired for either a brake or 
> as a generator on the main drive as well, for running on hills.  
> In either case, it would not free-wheel.  Large perminant magnet 
> motors don't spin as freely by hand as say an induction motor.  
> I really don't know.
> 
> Larry Elie
>