I'm interested in using a single momentary push-button switch to control a latching relay.

The idea is for the switch and relay to function as an on/off switch for a high-wattage load (13.8V DC, max 5A)—i.e., a single push gives power to the load, another single push cuts power to the load. There is a single power source (13.8V DC) which the relay and load will have to share.

What specs would be needed for the latching relay, and what kind of circuit would be needed to control it as described?

I posted another issue to seek suggestions more broadly for this application; the present issue is specifically to explore the latching relay option.

This is for a specific application; I'm happy to provide more details if it would be helpful.


1 Answer 1


One solution is an impulse relay:


12 V coil, 15 A contacts, toggle or alternate action, all in one component. Not complex at all, but also not cheap.

If you want to build a circuit and use a lower cost relay, the circuit is called a toggle flipflop or a bistable multivibrator. This requires two inverting devices - two transistors, two logic gates (NAND, NOT, or inverters), or one toggle flipflop IC (usually created with a D flipflop). The logic gates and flipflop IC would require an additional transistor as the relay coil driver.

Schematic on request.

If you go this route, there is a very common automotive relay that will do what you want. The contacts are rated for 20 or 30 A, which is comfortably overrated for long term reliability. Search 'automotive relay' on ebay or Amazon for lotsa. Another option popular on ebay is a small printed circuit board module with a relay ans wiring connectors on it. This makes for easier wiring.

ebay relay module


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