Put a resistor across the armature? That would shunt extra current to
the field.

Best regards,

Bob

On Thu, Aug 23, 2012, at 01:55 AM, KPL wrote:
> Hi, "world-wide brain" :)
>=20
> 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.
>=20
> 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?

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