The Stovebolt Site Forums The Shop Area The Electrical Bay Heater blower motor now turns wrong direction!

Been retrofitting our 55 1st series to 12 volt.

For the heater blower motor, my classic solution was to drop the voltage down to 6v by using a 1 ohm, 50 watt wire-wound resistor.

To prepare for that, I curiously took the motor apart to check the bearings and brushes.

Before disassembly the unit correctly spun counter-clockwise, thereby pulling the air through its radial radiator and into the heater assembly for distribution into the air-ducts.

Now after reassembly, the motor spins clockwise, which essentially pushes the airflow back into the radiator towards the truck cab and firewall (back of the heater unit).

I tried to reverse the power/ground leads but made no difference in rotation. I even tried flipping the 4-blade fan but.. nyet.

So, what has happened? How can this motor be made to spin back at its original counter-clockwise rotation?

You probably mis-assembled the brush holder when you put the motor back together. If the brushes contact the commutator in the wrong position the motor can run backwards.
Jerry

You can also change direction of rotation by assembling the magnet portion on backwards.
I recently did that on a Honda 4X4 starter.
Carl

Simple- - -install the housing 180 degrees out of position. It reverses the current flow through the armature. The only motors that reverse direction with polarity have permanent magnets, not field coils in the frame.
Jerry

Great set of motor assembly photos in your earlier post (with link), Denny! Can you post them again for future reference -- thanks.

Ok guys, I did as suggested and it now works counter-clockwise. Thanks for that tidbit, Jerry!

My only slight concern now is that after twisting the shells 180 degrees that the internal wiring isn't either rubbing on the brushes/commutator or impaled on the long thru-screws.

So, it's onward with getting it back into the heater housing and back into the truck ..and on with the more important job of upgrading the brakes.

Denny, the brush holders are not on exact center. when the housing is rotated 180 degrees, a different set of commutator bars is under the brushes and it sets up a different magnetic field. That causes the armature to rotate in the wrong direction when its field reacts with the one created by running current through the field coils. It's all a matter of geometry between the two sets of magnetic fields.
Jerry

Does the 'right hand grip rule' not apply here?

Denny, that brush holder would never cause the armature to spin "backwards". No way to get it "wrong". When a D.C. motor works the field(case) magnets "pull/push' the armature towards the opposite N/S poll. With a set of angled brush holders(like a starter motor) the angle sets the direction and maximizes the torque. Put them in offset the opposite angle, and the armature gets "push/pulled" the opposite direction. Lots of small D.C. motors use the angled brush holders just to increase the "starting" torque.

I guess I should have elaborated more.

And since you brought it up, the heater in the truck was from a '51 GMC (says GMC on the face plate and the heater build plate says: HC-06-51). So I would say that it was originally positive ground. But when put into my truck it did spin in the right direction ..which it is back to spinning now thanks to the instructs of half-turning the shells.

Sorry, didn't think it important to mention it's heritage at the onset.

Denny has his mind made up- - - -don't confuse him with facts!
Jerry

No confusion any more....is there!
dg

Getting muddy in here. Well it doesn't exactly smell like mud.