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I have a motor at home, it's a soviet era motor. It's connected to what seems to be a capacitor.

The setup pretty much look like the following one except the red box is much larger than the one on the picture and I can't see the markings. The one on the picture is 2uF 10% for 400v.

enter image description here

I was wondering if there was a particular reason why the capacitor is so big. If it's just that now capacitors for the same specs can be much smaller than the ones in the 70s.

Also I don't really understand the wiring of the motor. Mine is wired pretty much the same way except I have a switch that lets me change the rotation direction. I can't tell much for now as I'd have to dismount everything to access the readings to get a better idea. What I can tell is that this is a 127v AC motor. Here are the markings:

127v 30hz 6w

To my understanding, the capacitor is used to somewhat limit the current to something around 127v. So tecnically, I could replace the beefy capacitor by one of same value that I gather from broken fluorescent/led lamps?

The pictures are taken from this article: How to connect a 127v motor to 220v (Russian)

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  • \$\begingroup\$ To my understanding, the capacitor is used to somewhat limit the current to something around 127v Current is measured in Amperes (A). Voltage is measured in Volts (V). Capacitors can not limit current and DC voltage. Anyways, the size of a capacitor is determined by its capacitance and rated voltage. \$\endgroup\$ – CHendrix Feb 27 '17 at 14:10
  • \$\begingroup\$ It's an AC motor btw and I didn't meant "current" as in amperes but as in the normal way people use it. Like DC is direct current ans AC alternative current. Capacitor can be used to limit the current as it's AC and the capacitor should keep discharging every 50-60hz. \$\endgroup\$ – Loïc Faure-Lacroix Feb 27 '17 at 14:56
  • \$\begingroup\$ Your dropping voltage, not current. But is the motor marked 127 V? If yes, then it's like you say a series capacitor to drop the voltage although highly load dependent and a fairly dangouros situation. It could also just be a normal 230 V motor and a capacitor connected in paralell for phase compensation. \$\endgroup\$ – winny Feb 27 '17 at 16:11
  • \$\begingroup\$ @winny yes, I just checked and it's really 127v 30hz 6W. \$\endgroup\$ – Loïc Faure-Lacroix Feb 27 '17 at 16:35
  • \$\begingroup\$ Oh! Then series dropper. Terrible solution. \$\endgroup\$ – winny Feb 27 '17 at 16:53
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So technically, I could replace the beefy transistor by one of same value that I gather from broken fluorescent/led lamps?

In principle, yes. But the small motor in the picture is only rated for 6 watts of power, and you need to ajust the size of the cap depending on how much your motor needs. Note that the cap is also rated for 400 Volts (X or X2 cap).

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  • \$\begingroup\$ What do you mean by "X or X2"? \$\endgroup\$ – Loïc Faure-Lacroix Feb 27 '17 at 16:27
  • \$\begingroup\$ I was thinking that maybe a smaller cap would overheat? Which is why the capacitor is so big. Or it's just the design of the older cap is simply huge. \$\endgroup\$ – Loïc Faure-Lacroix Feb 27 '17 at 16:37
  • \$\begingroup\$ X1 and X2 refer to capacitors designed and tested to EN132400 for filtering of power lines. \$\endgroup\$ – Robert Endl Feb 27 '17 at 18:30

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