I am considering using the following example https://www.the12volt.com/relays/relaydiagram43.html

to use a 12v relay to generate a pulsed ground. However I have zero experience with capacitors, resistors etc (although i bought a bunch of resistors awhile back in case i might need them).

Anyway I am hoping someone can point me to what capacitor to use (electrolytic/ceramic etc) and how to properly wire this. Also can either the cap or resistor be wired backwards?

Would love to know more about all the numbers on capacitors to determine more but not sure where to find the info (yes ive been googling)

Thanks in advance for any insights.

pic of cap and resistor

So here is a picture of how i connected the cap and resistor - i tied them together

ran positive of capacitor to pin 85 on relay
ran negative of capacitor to pin 87 of relay

relay pin 86 is 12v power
relay pin 30 is supposed to be where pulsed ground for 1/2 second is when 12v is removed from pin 86

doesn't seem to work as i connected relay pin 30 to the negative side of a buzzer (while its positive connection was connected to a different 12v location)

  • \$\begingroup\$ Try aluminum electrolytic, they are inexpensive in that range. \$\endgroup\$
    – Gil
    Commented Jul 28, 2021 at 19:07
  • 2
    \$\begingroup\$ Do not connect an electrolytic capacitor backwards (unless you're wearing eye protection). 100% guarantee it will smoke & likely explode \$\endgroup\$
    – Kyle B
    Commented Jul 28, 2021 at 19:22

1 Answer 1


That’s an interesting example relay circuit, what do you plan to use it for? This context is probably needed to answer the part of your question about proper wiring.

There are lots of good intros available for Capacitors (e.g., https://learn.sparkfun.com/tutorials/capacitors/all). The link includes a section about identification.

Kyle B’s advice in the comments is important. Some capacitors are reversible and some are not. Smoke and explosive hot goo the likely result of getting that wrong https://hackaday.com/2011/05/18/blowing-up-capacitors/

Resistors on the other hand can be reversed. Again plenty of tutorials e.g., https://learn.sparkfun.com/tutorials/resistors/all

Edit: Updated with information based on the comments. The relay circuit referenced in the question was:

Relay Circuit Diagram

Fixed Polarised Capacitor symbol

The symbol used for the capacitor represents a fixed polarised capacitor of 1K (i.e., 1000) micro-farads. Where a farad is the SI unit for capacitance, and the symbol mu is the SI symbol for micro (the greek letter mu looks like a u with a long tail). The asymmetrical symbol reminds us to plug the negative side of the capacitor (curved side of the symbol) to the negative or ground side of the circuit, and the positive side of the capacitor (flat side of the symbol) to the positive side of the circuit. Polarized capacitors (e.g., electrolytic) usually have clear marking showing which side is which.

Capacitors are selected to exceed the maximum voltage of the circuit they'll be installed in. The rated voltage is also often marked on the capacitor.

So you could select something like a 16V 1KuF electrolytic capacitor. In the picture below you'll see that the negative side is marked with the vertical white chevron stripe down the can, with a minus symbol on it, pointing at the negative leg.
enter image description here

  • \$\begingroup\$ Thanks so much I will definitely read those links. The relay would be used to output a pulsed ground when 12v ignition is pulled from the relay. This pulse wil then go to another module to play an mp3 file in a module for a headlight chime reminder \$\endgroup\$
    – ddrumguy
    Commented Jul 28, 2021 at 23:39
  • \$\begingroup\$ @ddrumguy That sounds interesting, so using the capacitor and resistor marked in the schematic the12volt.com/12voltimages/constgtomg.gif are you all good to go? Remember to post back what you learn. \$\endgroup\$
    – RowanP
    Commented Jul 28, 2021 at 23:46
  • \$\begingroup\$ i certainly will, once i read through those links and determine what capacitor to order and try \$\endgroup\$
    – ddrumguy
    Commented Jul 29, 2021 at 2:29
  • 1
    \$\begingroup\$ There’s a FAQ about uploading pictures. meta.stackexchange.com/questions/75491/… and meta.stackexchange.com/questions/317576/… \$\endgroup\$
    – RowanP
    Commented Aug 2, 2021 at 5:34
  • 1
    \$\begingroup\$ @ddrumguy - Hi, No it is definitely not OK to add new information in an answer. That is forbidden on Stack Exchange sites - answers must answer the original question. As RowanP said, you should edit any new information into the question i.e. update the question (see the "Edit" link below the question? That is what you should use.) I will move your answer into the question as an edit (i.e. update) this time. Stack Exchange sites have different rules from typical internet forums. I recommend you look at the site tour and help center to see more site rules. Thanks. \$\endgroup\$
    – SamGibson
    Commented Aug 4, 2021 at 4:27

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