Tinman's coil shorting circuit

[massive]

if the coil is short circuited then it would have to behave like a shade ring

[minnie]

Oh,seychelles,you are a little gem!

[citfta]

Thats correct. In fact, it increases motor action when the generating coil is loaded-and by a large amount-while at the same time , power consumption decreases by at least half.
If you can work out why that is, then you will work out the rest of it.

I am pretty sure I know why that is.  Is it ok to post my thoughts on this here?  I have to leave for a meeting in a while but I can post my thoughts later this evening.

[citfta]

Well I don't see any objections to me posting my thoughts about the motor current going down when a load is placed on the stator coil so I guess I can go ahead and post my thoughts.

To understand what is going on you first have to understand how a shunt type DC motor works.  I realize a lot of you probably already know some or maybe most of this but I will review to make it easier to follow my thoughts.  In normal use a DC shunt wound motor has a current applied to the field (stator) coils.  When armature voltage is applied the interacting magnetic fields cause the armature to rotate.  At the beginning of the rotation the armature current is only limited by the resistance of the armature.  As the armature speed begins to increase the magnetic field from the field coils begin to generate a voltage in the armature coils that opposes the applied voltage.  This is what is normally called BEMF or CEMF.  As the armature speed gets higher the BEMF goes higher also.  At a high enough speed the BEMF limits the current through the armature to the point there is only enough current flowing through the armature to overcome the friction losses and power the load.  I realize that on a lot of OU type forums BEMF is considered the enemy that must be somehow overcome.  In fact the BEMF limits the current and controls the speed of the motor.

Now what would happen if there were no current flowing through the stator coils?  There would be almost no BEMF generated and the motor would have very little torque.  Also the current will be much higher than when there is a field produced by the stator coils.   In the small motors like are being worked with in this thread there is a small amount of residual magnetism left in the stator poles to allow the rotor to rotate.  Also the armature coils are wound with wire of a small gauge which limits the current through the armature.

In large motors if the field current is lost the armature current can go up to thousands of amps or at least until something blows like a fuse or breaker.  In industrial motor controllers a sensing circuit will cut off the armature voltage if field current is lost for some reason.

In the motor Brad is showing in his video he has one stator coil shorted if I understand correctly.  This allows current to be induced in that coil which in turn produces a magnetic field to oppose the field from the armature and thus allow the motor to operate.  However since there is only one field coil energized the BEMF is weak and therefore the torque is weak and the current draw is higher than normal.

When he connects the other stator coil to a load now current is allowed to flow in that stator coil which causes the BEMF to go up.  This limits the armature current even more and creates more torque from the motor.  Thus we see the armature current go down when a load is applied to the second stator coil.

It appears he also has some other things going on with his circuit board that enhances this effect but I think basically the reason the armature current drops is because of the energizing of the second stator coil which increases the BEMF.

Brad, if I have a mistaken idea about this feel free to say so.  And if you don't want to say anymore than just that I am mistaken that is OK too.  Just trying to answer the question you posed.  By the way I think this is an ingenious way to get more power from a motor and make the motor more efficient at the same time.

Respectfully,
Carroll

[shylo]

 In normal use a DC shunt wound motor has a current applied to the field (stator) coils.
Hi Carrol,
I don't have an understanding of this. In order to have current you need R and V correct? (ohms law)?
You have to supply voltage to get the current? (correct)

When armature voltage is applied the interacting magnetic fields cause the armature to rotate.
But tinman only uses one supply does he not?

I only connect a battery to the brushes and get rotation, I don't feed anything to the field windings, but yet they put out a voltage source, which can power a load, albeit alot less than I put in.

The single supply must make the rotor appear as constantly changing fields, as a result constantly changing fields in the stator ,but timed perfectly to cause rotation ??

I'll reread your post try to figure it out.
Thanks artv