1
\$\begingroup\$

I have a NO DPDT relay, non latching, 12V coil controlled by transistor. One pole is switching fine. The other pole is stuck closed until I give it a few taps with a screwdriver. These are new production boards and the issue is seen on a handful of units.

I assume that the design is ok given that 1 pole is switching. Could this be a batch problem with the relay or a SMT process issue. I would be keen to hear if anyone has experience this before and what caused the issue. The relays are made by NEC and purchased through proper channels. I don't believe that the boards are washed meaning that no liquid is getting into the relays.

Thank you

\$\endgroup\$
5
  • \$\begingroup\$ "Could this be a batch problem with the relay or a SMT process issue" yes. Quite possible. \$\endgroup\$
    – Elementronics
    Commented Nov 26, 2021 at 10:54
  • \$\begingroup\$ I have also ruled our contact welding as these relays are new off the production line and have not had any current through the switched side. \$\endgroup\$
    – RoyalAce
    Commented Nov 26, 2021 at 10:58
  • 1
    \$\begingroup\$ Any evidence the relays were overheated during the SMT process? Is there a vent, and if so, was it possibly opened prematurely? \$\endgroup\$
    – Spehro 'speff' Pefhany
    Commented Nov 26, 2021 at 11:21
  • \$\begingroup\$ Thanks Spehro - what signs would I be looking for? I dont see any vents on this relay or in the datasheet. \$\endgroup\$
    – RoyalAce
    Commented Nov 26, 2021 at 14:36
  • \$\begingroup\$ Doesn't "NO" exclude a DT relay ? How can it be both ? \$\endgroup\$
    – tobalt
    Commented Nov 26, 2021 at 17:26

1 Answer 1

Reset to default
1
\$\begingroup\$

The relay contacts may get stuck if the current flow at the moment the contacts close is quite large. This can be thought of as some sort of welding.

If a contact pair in a DPDT relay is switching a sub-circuit which causes large inrush currents (e.g. capacitive loads such as an off-the-line device having a bridge rectifier and a large capacitor at its input) then it's quite normal to have the contacts getting stuck. You can use high inrush-type relays for this purpose.

\$\endgroup\$
1
  • \$\begingroup\$ No load has been connected. Hence, not contact welding. Thanks \$\endgroup\$
    – RoyalAce
    Commented Nov 26, 2021 at 11:12

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.