How Do I Wind a doughut suppression core for a brushed 240VAC Universal Motor

[SuzyC]

Right now i have both brush wires wound together as a single winding on a 2-in diam core, that is, bifilar.
In other words, both the brush wires are wound to enter and exit in the same direction on the core as if they were both just one wire and then they split up at the end of their winding together and go directly to each brush.

Does this work or am I summoning the demons of EMI to a toroid party?

[Terry Bites]

You need to wind a "common mode choke", see our mate doing just that


If there is a significant voltage across the motor terminals make two separate windings.
You don’t want an insulation fail.

A toroid is just a doughnut in rigor mortis, don't be affraid.

[SeanB]

It will work, though you can also add a 10n class Y capacitor across the terminals by the motor, and if it is not grounded you can also add one from each terminal to the case as well.

[SuzyC]

Thanks to all. My mcu controlling the Universal Motor (whose IntOSC SysClk is set at 64mHZ) was acting very erratic but is now working correctly and stable.

Apparently, I wound it right!

If I add a class Y cap across the motor as a snubber(1uF in series with 22-ohm across the brush contacts), might I cause the brush arcing to be more violent because the snubbing capacitor would be charging/discharging into the brushes at high currents?

The Youtube video about this subject is so Bubba-ish!. Typical Trailer Park Tech info. Here's a man who somehow knows how but doesn't know why things work, but this doesn't stop him from playing expert.

[T3sl4co1l]

An RC will be fine, and I would recommend such as it gives termination for the (diff mode) inductance of the CMC.  Maybe 47 or 100 ohms would be better, but it depends on everything (CMC windup, what's behind it; motor ratings, lead length, isolation capacitance, etc.).

Some CM termination may be desirable as well, shunting noise to the motor casing as close as possible -- assuming you are able to make a connection to it of course.

Note, you'll be hard pressed to find a Y-cap rated 1uF I think, but maybe you meant X type, which is fine.  BTW, is this phase-controlled or anything?  Just on/off?

Tim

[SuzyC]

Motor is being used in an old front loader washing machine with pulley-belt motor to drum drive. The washer now serves well as a semi-precious stone polisher.

Its a slow grind.

Motor is 2-Amp type, and is phase-controlled. Always using phase-control, with kickstart code, and once the tub is started up, uses PID speed control by my code.

Yes, I have (salvaged from ATX P/S) yellow plastic rectangular X-type caps (.1uF to 2uF all labeled at 250VAC, label shows possibly every safety spec abbrev. possible)for use to make a snubber 

Since things are back to normal, I think the EMI was radiating not from the motor case, but from fast dI/dt dV/dt and  the length of the motor wiring, which is about 3-ft from my controller to the motor. With the CMC, the leads from the choke to the brushes is now less than 2-in and the inductance of the CMC makes the (previous to adding choke) sharp rise/fall times to be very much longer..

I picked 22-ohm as a possible snubber min value to safely limit the cap peak current to < ~12-amps at 240VAC, but higher values of resistance may greatly decrease EMI suppression. I am not  using the snuuber yet because I am not sure if the peak voltages developed across the brush contacts may be too high and would cause these 250VAC caps to fail. Besides, as Bubba would say, its working now.

[T3sl4co1l]

Oh that makes quite a bit of difference then.  You don't want a large cap between phases.  Just a snubber at the controller will do to handle winding inductance (up to maybe 0.47uF, with modest resistance), and a snubber or two at the motor to handle arcing (say 10nF and 47 ohm?).

250VAC should be fine.

Tim