1
\$\begingroup\$

I have a device with a 12V battery pack (it's actually eight AA batteries in a harness.)

In taking it apart, I see that it has a small capacitor in series with the positive side of the supply. So, just a small indistinguishable capacitor between the + terminal of the 12V battery pack and the switch.

I'm seriously questioning myself here. Why is there a capacitor here? Won't that break the voltage? It's not in parallel, and it's DC.

What am I missing?

Edited to add this picture: What I believe should be a capacitor, but may not be.

It's heavily corroded around the leads, the right pole in the image connected to one side of a switch. The left side pokes through that plastic to the positive terminal in the battery harness.

To be honest, there isn't anything more to this circuit on this side. It goes to a motor, that's all. The negative terminal goes directly to the motor.

Since the comments are suggesting this is likely a fuse, that would certainly explain why I have no luck figuring out what kind of capacitor this is. Also explains why this circuit works, since it's not a capacitor.

\$\endgroup\$
3
  • 11
    \$\begingroup\$ There's a fair chance that it's not a capacitor, but something like a self-resetting fuse. Difficult to tell with no picture or description. A photo would be best. \$\endgroup\$
    – Cristobol Polychronopolis
    Commented May 20, 2022 at 18:21
  • 1
    \$\begingroup\$ Small Raychem Poly Switches look very much like small radial capacitors. The Raychem parts are gold / yellow, if that helps. \$\endgroup\$
    – Dwayne Reid
    Commented May 20, 2022 at 18:40
  • \$\begingroup\$ @CristobolPolychronopolis Thanks for your help. I would never have guessed this wasn't a capacitor. \$\endgroup\$
    – Gorchestopher H
    Commented May 20, 2022 at 21:00

2 Answers 2

Reset to default
3
\$\begingroup\$

It is a self-resetting fuse aka "PTC" device. Here is a datasheet which shows a device with similar markings, and (likely) identifies it as a 650mA 60V PTC with breaking capacity of 40A.

enter image description here

\$\endgroup\$
2
\$\begingroup\$

Likely a power thermistor for inrush. Power thermistors greatly increase or decrease their resistance depending on how much current is running through them. You can get ones that are high resistance at the start and decrease with current (NTC type inrush limiters) or ones with low resistance that increase when current gets too high (PTC type inrush limiters).

If you have a multimeter, you can test capacitance, but it's likely an NTC/PTC inrush limiter.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.