1960s ‘59-‘62 blower motors

[Cadman-iac]

Bruce and TJ,

  Learn me somethin' here if you would. I'm trying to wrap my head around this. On a 2 brush motor with field windings that would typically be used for a blower motor, how does swapping the brush wires change the rotation?
As I understand it, on the armature the power goes in through one of the commutator bars, around the windings and back to the commutator bar exactly opposite from the input, then out through the second brush to ground. I think anyways.
Moving the wire for the brushes from one contact point to the other only makes the brush wires longer, there's still just an input and an exit brush, or a positive and a negative brush.
The power still flows through the armature exactly the same way, does it not?

 The only way that I'm aware of to reverse a motor like this is to ground the original positive wire, and apply 12v positive to the case and the motor will run backwards, but I've only ever done this as a bench test. It's not something you'd ever want to do on the car

 Now would changing the field polarity cause it to run backwards?

Please keep in mind I'm not an electrician, I know just enough to be dangerous as the saying goes.

Rick

[TJ Hopland]

You can't really make a blanket statement about how to reverse a motor without knowing what type it is and how to was constructed.  I thought auto blowers were typically permanent magnets in which case it is as easy as reversing the input power. 

If its something that has field coils then it depends on a lot of factors how you would reverse it.  You can have a design that you just flip the input like a permanent magnet motor but you can also have designs where you have to be able to change just the field or armature.  A starter is an example of that type, you can convert a car from pos to neg ground and the starter doesn't spin the wrong way.

You would use the different motor types depending on the requirements.  Cost, longevity, starting torque, peak torque, do the torque requirements change depending on speed?  Do you need it to change speed?  Do you need it to regularly run in both directions?  Is the torque requirement different in different directions?  Do you care about efficiency?  Size?        

[bcroe]

Bruce and TJ,  On a 2 brush motor with field windings that would typically be used for a blower motor, how does swapping the brush wires change the rotation?
As I understand it, on the armature the power goes in through one of the commutator bars, around the windings and back to the commutator bar exactly opposite from the input, then out through the second brush to ground. I think anyways.
Moving the wire for the brushes from one contact point to the other only makes the brush wires longer, there's still just an input and an exit brush, or a positive and a negative brush.
The power still flows through the armature exactly the same way, does it not?
 The only way that I'm aware of to reverse a motor like this is to ground the original positive wire, and apply 12v positive to the case and the motor will run backwards, but I've only ever done this as a bench test. It's not something you'd ever want to do on the car
 Now would changing the field polarity cause it to run backwards?
Rick

To reverse a DC brush motor, you must reverse either
the field or the armature magnetic poles.  Reversing
the wires to the 2 brushes causes the current to flow
into the opposite commutator bar and in the opposite
direction around the winding, reversing the magnetic
field. 

Reversing the stator magnetic field achives the same
thing, hard to do with permanent magnets.  The motor
construction will determine the easiest way. 

Some motors are built for easy reversal, one way for
a DC motor is with 2 stator windings wound in opposite
directions, either then feeding thru the brushes. 

Some brush motors with no permanent magnets (electric
drill) are called universal motors, because they run
on either DC or AC.  This works because reversing the
power does not reverse the motor.  Bruce Roe

[Cadman-iac]

To reverse a DC brush motor, you must reverse either
the field or the armature magnetic poles.  Reversing
the wires to the 2 brushes causes the current to flow
into the opposite commutator bar and in the opposite
direction around the winding, reversing the magnetic
field. 
  Bruce Roe

  Bruce,

This is the part that is confusing me here.
Because the armature rotates, and each brush only contacts one or two of the commutator bars at a time, and they are 180° apart, if the positive voltage is going in one and out of the other, swapping the brush leads to move the positive side 180° from its original location, if the armature rotates 180°, then isn't that exactly the same as before you moved the brush leads?
Because the windings on the armature are not changed, the field generated in those windings is unchanged as well, and thusly, would still operate in the exact same way.
Or am I still missing something here?
I admit that it's been a few years since I've worked on a blower motor, and I don't remember if I'm getting a window motor and the blower motor mixed up, but on the older blowers, I thought they had field windings instead of permanent magnets, but my memory may be suspect here too.
If that's the case, I'll have to go take apart one of the blowers I'm thinking of and double-check myself.
Thanks for taking the time to edjumakate an old fart like myself.

Rick

  To add here, I know that a window (and antenna) motor with field windings uses only one at a time, and each one is wound opposite of the other in order to reverse the magnetic field.
 On a permanent magnet window motor, the power and ground wires are switched to change the rotation direction.
 

[bcroe]

As I recall my 62 had a wound field wiper motor, but
the nearly identical 63 used a permanent magnet field. 

If your brushes were feeding a couple slip rings (like
an alternator), the current would always flow the same
in the armature, rotating the magnetic field.  But your
motor brushes contact a winding and generate a magnetic
field approximately half way between attracting one
field pole, and repelling the other.  When the armature
turns enough to contact the next commutator bar, the
current flows thru a new winding that is positioned in
THE EXACT SAME POSITION as the previous winding was, so
it generates a magnetic field in the SAME position.  The
armature rotates, but due to the switching action of
the commutator the magnetic field stays pretty much
in the same place.  A generator does the same thing
in reverse, the generated power is connected at the
right time by the commutator, to give approximately
DC output. 

An alternator is like an inside out generator, the
slip rings generate a fixed field in the rotor.  An
alternating current is generated in the fixed outer
windings, and solid state diodes are used to get DC.
The diodes eliminate the heavy wear and radio noise
from arcing with brushes. The unit generates much
more energy per pound.  But diodes are not as
efficient, you need to drive them with at least 16V
to get 14V out to the battery.  This starts to look
pretty bad in a 6V system, 1/4 of of voltage lost. 
Bruce Roe