There is a behaviour that is needed to be achieved with a circuit, that I believe can be done with a relay. However, OIcan't see to get it right..

The scenario is the following:

  • The relay will control the connection of a high power supply (30A) to a load
  • Besides this, there is one signal wire and one low power supply
  • The relay should turn on when the signal goes High, but feed off the low power supply
  • After the signal goes High, the relay must stay on as long as the low power supply is available, even if the signal goes Low.

What relay circuit should I use for this?


  • 1
    \$\begingroup\$ I don't udersand anything you wrote. \$\endgroup\$ – Marko Buršič Oct 9 '18 at 19:12
  • \$\begingroup\$ @marko Sorry, I forgot the Enter before the list. I've fixed it. Please check again. \$\endgroup\$ – AmiguelS Oct 9 '18 at 19:15
  • 1
    \$\begingroup\$ Sounds like a latching relay \$\endgroup\$ – Gregory Kornblum Oct 9 '18 at 19:15
  • \$\begingroup\$ @Gregory But won't a latching relay retain its state after the supply is gone? \$\endgroup\$ – AmiguelS Oct 9 '18 at 19:20
  • 2
    \$\begingroup\$ At 30 amps, you are far beyond the domain of casual internet advice. You need direct assistance from someone who knows what they are doing, and you'll need to present them with full details of exactly what you are switching. The control rules are not your most pressing concern here - the challenge of making and especially breaking a 30 amp circuit is. \$\endgroup\$ – Chris Stratton Oct 9 '18 at 19:24

A latching relay might get you what you need, however, you may need the circuit to reset itself when power goes off and on.

You can do this with two relays:


simulate this circuit – Schematic created using CircuitLab

The signal pulse turns on the relays. Once the first relay is on, it continues to keep itself on until the low power supply goes away.

As long as relay 1 is on, relay 2 will also be on, even if the pulse line goes low.

Depending on the circuitry that is generating the pulse, you may need to put a diode in line there.

| improve this answer | |

Strange, I thought I already answered this but perhaps I forgot to actually hit Post.

You need a dual-coil latching relay. When current is passed through the first coil it closes the contacts. The contacts then remain closed until current is passed through the second coil, which then opens the contacts.

Search Digikey, Mouser, or your favorite supplier for "dual coil latching relay" to get loads of options that should suit your needs.

| improve this answer | |

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.