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I have an old electrical motor from the 1970s. It does not work as it should, and I suspect the capacitor attached to it. It has two legs and reads: 0.1uF+2x2500pF ~250v. I am not familiar with that "+2x2500pF" way of writing it. What should my multimeter read when measuring and what is the idea of the way to write its capacitance? Currently imy multimeter reads something like 0.177uF when connected to the two legs.

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    \$\begingroup\$ Is there a third connection to the capacitor that looks different? For example, it might be attached to the chassis with a nut. \$\endgroup\$ Oct 21, 2020 at 12:00
  • \$\begingroup\$ There are two cords coming from the capacitor, those were the ones I measured between. But yes, you are right. The capacitors body is made of alloy and it is attached to the motor with a bolt. So it could be that is a "3rd leg" \$\endgroup\$ Oct 21, 2020 at 12:11
  • \$\begingroup\$ Also, just updated the question with a "2x" notation I left out by mistake \$\endgroup\$ Oct 21, 2020 at 12:13

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schematic

simulate this circuit – Schematic created using CircuitLab

Figure 1. The internal arrangement.

C2 and C3 shunt high frequency noise to ground.

What should my multimeter read when measuring and what is the idea of the way to write its capacitance? Currently my multimeter reads something like 0.177 uF when connected to the two legs.

Your multimeter reading looks about right. Electrolytics have a very wide tolerance on the capacitance value. The motor fault may be something else.

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  • \$\begingroup\$ Is this kind of capacitor electrolytic? If it is, it would be an unpolarized one, right? Non-electrolytics also have a wide tolerance. \$\endgroup\$
    – mguima
    Oct 21, 2020 at 13:18
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    \$\begingroup\$ It's not electrolytic at such a small value from that period. Paper in oil ("Visconol") was commonly used for 0.1uF : check DC resistance > 10Meg (and to case), they did develop some leakage current. \$\endgroup\$
    – user16324
    Oct 21, 2020 at 13:38

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