I have a handheld wireless rechargable mini-vac (like a Dustbuster). The charger outputs 19V DC 150mA.

My cat chewed through both wires on the adaptor. Both wires are completely black with nothing to indicate what's positive/negative. The plug and the barrel jack/coax connector both solid moulded plastic with no clues either. I've spliced them back together but does the polarity of the wires matter?

I vaguely remember from physics at school that if you reverse connections to an electric motor it spins in the other direction. In this case, would it force the vacuum's battery to discharge and then not charge? Or damage the vac altogether?

Does it matter or should I just buy a new adaptor?

  • 1
    \$\begingroup\$ Buy a new one. Yes polarity matters \$\endgroup\$
    – MCG
    May 20, 2018 at 17:09
  • 1
    \$\begingroup\$ The problem isn't the motor - it's the battery. If you reverse connect it you will be reverse charging it and damage or fire may result. The product should have reverse polarity protection but it may not. \$\endgroup\$
    – Transistor
    May 20, 2018 at 17:13
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    \$\begingroup\$ Just to make it simple, yes it matters. But the details of what will happen if you do it backwards are hard to predict. It could lead to permanent damage of the battery or charger or vacuum. That being said, the wire usually has some kind of marking on it, even if it is not color, there will be a ridge or something on one of the wires. Also, looking at the plug, we can guess the polarity. Usually the most accessible contact is ground, and the less accessible contact is the positive voltage. \$\endgroup\$
    – user57037
    May 20, 2018 at 17:18

1 Answer 1


Absolutely YES ...the polarity does matter.

Even though your cable ma not indicate any difference in the wires, your power supply should have an indication.

Most labels show the polarity of the pin and body of the plug:

Here's one for the Dustbuster power supply:

enter image description here

Here I shows the central pin as the positive terminal.
If there is no indication on the wire to help you will need a multimeter to ascertain which wire goes to the pin on your cable end ….and measure the two wires from the power supply to ascertain which one is positive.

Most devices include reverse voltage protection since it's easy for users to use the wrong power supply, but it's anyone's guess as to whether your device is protected.
If you don't have a multimeter ….they are dirt cheap, so get one.

  • \$\begingroup\$ Many thanks. I do have a multimeter but don't really know how to use it. I'll just try and buy another adaptor. \$\endgroup\$
    – Gavin Ward
    May 20, 2018 at 18:01

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