# Can anyone explain how this battery charger works?

#### Sunny Rio

Feb 13, 2022
2
https://imgur.com/a/b8l5qKQ

Look at the circuit diagram. The positive of the battery is only connected through a capacitor. How can a capacitor possibly pass DC current to allow the battery to charge?

#### TCSC47

Mar 7, 2016
148
In the diagram the yellow disc component has been assumed to be a capacitor. However, as you say the circuit would not work if it was. The yellow disc has to be something else like a thermal fuse, or a current limiting device of some sort. I am writing this late at night and I am too tired to analyse the rest of the circuit, I'm afraid.

#### Harald Kapp

##### Moderator
Moderator
Nov 17, 2011
13,736
Where is the image from? The original website could help solve the riddle. I agree with @TCSC47 that this is possibly a current limiting device, e.g. an NTC.
The symbol in the schematic diagram is incorrect in any case.

#### Sunny Rio

Feb 13, 2022
2
Where is the image from? The original website could help solve the riddle. I agree with @TCSC47 that this is possibly a current limiting device, e.g. an NTC.
The symbol in the schematic diagram is incorrect in any case.
It's my drawing and my photos of my cheap cordless drill NiCad charger. I agree it's a current limiter. I didn't know those existed pretending to look like capacitors!

#### Harald Kapp

##### Moderator
Moderator
Nov 17, 2011
13,736
Take a picture of the component from the side so we can see the inscription.

#### cjdelphi

Oct 26, 2011
1,166
It's my drawing and my photos of my cheap cordless drill NiCad charger. I agree it's a current limiter. I didn't know those existed pretending to look like capacitors!

that's definitely a thermistor ntc or ptc, is it there to prevent an inrush or is it there to decrease current are you positive your circuit is correct?

#### cjdelphi

Oct 26, 2011
1,166
try measuring the resistance before when cool then switch off and measure again

probably limits the current when hot

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