I found this component in parallel to a switch and 100nJ capacitor. My guess it that it is part of the de-bouncing circuit. Can somebody tell me what it is?

enter image description here

The blue disc has a diameter of about 8mm.

In case it helps:

  • this was part of a 12V circuit.
  • the mechanical switch may activate either a relay coil or a semiconductor switch
  • the label reads to me like "HEL (weird 7-like symbol) D560K"
  • \$\begingroup\$ How large is it in reality approximately (mm)? \$\endgroup\$ – jippie Apr 29 '13 at 10:07
  • \$\begingroup\$ @jippie Should have put in a scale. It's about 8mm in diameter. \$\endgroup\$ – ARF Apr 29 '13 at 10:09
  • \$\begingroup\$ It looks very much like some PPTCs (polymer resettable fuse) I have lying around. \$\endgroup\$ – Anindo Ghosh Apr 29 '13 at 10:09
  • \$\begingroup\$ What happens when you measure it for resistance and capacitance? \$\endgroup\$ – jippie Apr 29 '13 at 10:10
  • \$\begingroup\$ @AnindoGhosh Interesting, but does this make sense in parallel to a switch? A fuse would have to be in series, no? \$\endgroup\$ – ARF Apr 29 '13 at 10:11

This is a Hongzhi Enterprises (HEL) brand metal-oxide varistor.

The website doesn't mention pending safety approvals, but this part has both UL Recognized component and (what looks like) CSA marks on it. It's not surprising that the website is a little out of date, I've seen it quite often with offshore smaller suppliers.

I've never used this brand of part, so I cannot speak for its robustness.


enter image description here

I agree with others that this is most likely intended as a transient clamp meant to suppress the inductive kickback of a de-energized relay coil.

  • \$\begingroup\$ Thank you very much! I am in awe that you found the actual specs. \$\endgroup\$ – ARF Apr 29 '13 at 13:47
  • \$\begingroup\$ Sometimes I luck out :) \$\endgroup\$ – Adam Lawrence Apr 29 '13 at 18:40

It wouldn't surprise me if it was a Metal Oxide Varistor: -

enter image description here

The first three characters are 10D which means 10mm diameter. It is rated at 470V. I suspect the one in the question is 7mm diameter and is rated for 56V.

They come in various shapes and sizes - these are just blue ones but they are manufactured in different colours. Here are some more blue ones: - enter image description here

I can find an MDE-7D560k which seems to be 7mm diameter - its spec may help you decide. The data sheet can be found here

  • \$\begingroup\$ +1, I was just off checking how MOV part numbering works and came to the same conclusion but you beat me to it. \$\endgroup\$ – PeterJ Apr 29 '13 at 10:51
  • \$\begingroup\$ I was having doubt between a cap and a varistor. Does a 56V varistor make sense in this application? \$\endgroup\$ – jippie Apr 29 '13 at 10:52
  • \$\begingroup\$ @jippie, I was thinking it's probably to protect against inductive kickback in the case of a coil. Depending on the switch configuration probably just across the switch for assembly convenience. \$\endgroup\$ – PeterJ Apr 29 '13 at 11:11
  • \$\begingroup\$ @PeterJ Thanks for clarifying the use of the component in this configuration. Also thanks to Andy for his quick answer. \$\endgroup\$ – ARF Apr 29 '13 at 13:48

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

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