After reading this:

Is there any advantage in running a universal motor on DC power?

I want to know, does it improve the motor characteristics if you supply the motor flat DC instead of pulsed (fully rectified) DC?

And what happens when you want to speed-control (e.g. PWM) these two methods, is there a significant advantage in those cases?

To conclude: what's the shape of voltage and thus switching-type that you can best use to speed-control a universal motor to maximize motor characteristics (less heat/noise/friction/wear, more efficiency)?


  • \$\begingroup\$ From a system point of view, and assuming a single-phase supply, filtering the mains to give smooth DC requires a large electrolytic reservoir capacitor (at the mains frequency x2) and that may well determine how long your system lasts before service is required. An average life of a few thousands of hours at high temperature is not atypical for such a component. \$\endgroup\$ – Spehro Pefhany Oct 15 '17 at 23:43
  • \$\begingroup\$ While capacitor issues aren't to be overlooked, in fact quite a lot of industrial motors get their power by way of rectifying the mains to a DC capacitor bank and then synthesizing 3-phase AC from that at a variable frequency - while many of these have 3 phase input which helps a little, there are derating tables for single phase input. Hopefully these electronics aren't in the hottest part of the machinery, have a cooling fan, etc - point being that this is a routinely solved problem. But in fixed installations, while universal motors are mostly used in hand-portable equipment. \$\endgroup\$ – Chris Stratton Oct 15 '17 at 23:58
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    \$\begingroup\$ Universal motors aren't really well suited to controls applications as their output torque is proportional to \$ I^2 \$ \$\endgroup\$ – sstobbe Oct 16 '17 at 1:53

Pulsed DC voltage from a single phase bridge rectifier will mean that the current in the feild and hence the armature will be pulsing to some extent .The total inductance would have to be infinite to make the current waveform pure DC.The pulsing current will cause more motor losses than pure DC like a battery.But the losses are lower than a straight 230 VAC supply .

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