View Single Post
Old 08-06-2009, 09:22 AM   #2153 (permalink)
EcoModding Lurker
bones007's Avatar
Join Date: May 2009
Location: Brampton, Ontario, Canada
Posts: 15
Thanks: 0
Thanked 2 Times in 2 Posts
Originally Posted by KcElectricMan View Post
Since the idea of using a Atmega16 is being kicked around how about lets think about putting an H-Bridge into this so we can go in reverse without a transmission. Not everyone would need to build that part of the circuit if they only wanted forward rotation.
There are a couple problems with trying to reverse a series wound DC motor with an H-Bridge.

As current flows through the field windings it sets up a magnetic field. A second magnetic field is generated in the armature that is always in opposition to the first, because the armature current is switching direction from the action of the brushes. Because the field and the armature are connected in series, if you swap the direction of the current through the motor, you swap both the direction of both the field and the armature magnetic field and the result is a double negative. The motor continues to turn in the same direction. These motors are also known as Universal Motors as they can run on DC or on AC power.

A second problem with an H-bridge is that it requires more switching components (mosfets).

Originally Posted by KcElectricMan View Post
An added benefit to this setup is the possibility to regen during breaking. Want to slow down? throw on the P- channel at a low rate. Kinda like a a Jake brake on a semi-tractor. Not full braking just a couple of hundred amps at the most.
I found an interesting study on series wound DC motors and regeneration. The author goes through the basics of series wound motors and used a half bridge with two contactors to achieve the reversing and regeneration functionality for a series wound DC motor. See pages 17-19 of:
  Reply With Quote