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I have a technical problem where the cable of a food mixer has voltage across its cable when unplugged. When I measure it with a multimeter at various times after being unplugged it shows a voltage rating that decreases the more I wait after unplugging it.

Is this normal for such a device?

I opened the mixer and it has an AC motor with a capacitor. I assume the capacitor is not discharging immediately after being unplugged out of the socket but needs some time. This seems to be quite dangerous given someone was to touch the two leads of the unplugged cable.

Is this normal or is something wrong with the capacitor inside?

The voltage I measure goes from 50V to 5 volts depending on how much time I wait after unplugging it.

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  • \$\begingroup\$ I've seen this on older appliances. \$\endgroup\$
    – Andy aka
    Commented Aug 31, 2023 at 13:39
  • \$\begingroup\$ I touched both leads with my finger after unplugged and it gave me a small brief shock \$\endgroup\$
    – LEXOR AI
    Commented Aug 31, 2023 at 13:40
  • \$\begingroup\$ Even if you believe that a capacitor is too small to give you a lethal shock, if it has been energized to mains voltage, NEVER touch one lead with one hand, and the other lead with the other hand. If you feel compelled to touch both leads, do it with the same hand (or better yet, use a voltmeter to test, and a resistor to discharge. \$\endgroup\$
    – Math Keeps Me Busy
    Commented Aug 31, 2023 at 14:27
  • \$\begingroup\$ Yeah I know. I first measured it with a voltmeter it showed some voltage. And then I touched both leads with the same finger quickly to make sure there is really voltage on it. \$\endgroup\$
    – LEXOR AI
    Commented Aug 31, 2023 at 14:53

1 Answer 1

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It isn't good for a voltage to be present on the plug, but it isn't unusual either.

There ought to be a resistor across the capacitor to discharge it when you unplug the mixer. Some cheap devices don't have a resistor. Other devices have a resistor so you won't get zapped. Other devices were built with a resistor but the resistors sometimes break over the years.

Solder a 470k resistor across the capacitor and the voltage should sink fast enough to not be a problem. Use a resistor with a power rating of at least 0.5 watt.

The capacitors are generally small so they don't hold a lot of energy. The zap from touching the prongs of the plug is slightly painful but unlikely to hurt you.

I've been zapped by small appliances with universal motors - the old mixer from the 1970s that we used to have was pretty bad about it. I've made it a habit to touch the prongs of the plug to a piece of metal to discharge the capacitors any time I unplug such devices. The easiest is to touch both prongs to the water faucet in the sink after using the mixer.

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