I have several hundred brushed universal AC motors in the field they start life as a big Milwaukee drill. >From the manufacturer the field is run in series with the armature and the reversing switch only reverses the polarity of one of the two coils. One of our adaptions adds a beefy bridge rectifier to the field coils so we can control the unit with a off the shelf DC PWM motor controller. Net effect is the bridge rectifier is in series with the armature, the field is run across the bridge. -Denny On Thu, Aug 23, 2012 at 1:55 AM, KPL wrote: > Hi, "world-wide brain" :) > > I am using an old washing machine motor to drive my small metalworking > lathe, using a very simple U2008- and triac-based speed controller, > which does not work too well. Lathe is not used too often, so I am not > going to invest lots of time or money in that, but anyway, I am > thinking of a better controller. > > I have checked several different appnotes and docs about universal > motors, and general conclusion is to use DC drive with PWM, which > should not be extremely difficult. > But I have not seen any docs that would talk about steering the field > winding separately from the collector. Lathe requires a lot of torque > at low speeds, so probably I could get some advantage with higher > current in field winding, when voltage on collector is low. > By default field winding is connected in series with collector, so it > gets less power, when voltage is reduced for lower rpm's. > Any thoughts? > > > -- > KPL > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .