I've got a project I just put in place and I've run into troubles and it's a little above my knowledge level so I'm looking for some suggestions.

Goal: Control a 220vAC pump from 2 locations

Implementation: I used a 220vAC relay triggered by 12vDC. There are 2 12vDC momentary switches, with red/green halo's, that connect to a latching relay. The latching relay drives the 220v relay and the momentary switches pulse to ground on the latching relay. A 220vAC to 12vDC power supply is connected to the line in and provides 12v for the system.

Problem: If the system if off, I can turn it on with no issues. If it is running, the latching relay will sometimes try to switch over but most of the time it will only "half click" and the main 220v relay seems like it tries to weakly change. A few random pressed of the momentary switches and it will shut off. Sometimes I see a quick spark in the 220v relay when trying to go from running to not.

More detail: The coil for the 220v relay is connected to the NC output of the latching relay. When the system is energized, the coil for the 220v relay is energized and the pump turns on. I set it up this way so if there was a power interruption, the system would default to a running state if there was a power interruption. I have a master switch to over-ride this function.

I tested everything after the 220v-12v power supply before I hooked everything up and it worked without issue. My guess is that when the latching relay is triggered and there is a load on the 220v relay, something is happening that is either causing a quick voltage drop causing the latching relay to reset or the power supply is doing something strange.

Here's a schematic I drew up that is close. It didn't have a latching relay so I kind of threw in connections to make my own. The DPST switch lit weird if I tried to interrupt the coil, so that was removed. The DPST switch is just connected to the main power now.


simulate this circuit – Schematic created using CircuitLab


Power supply: https://www.amazon.com/dp/B07SJRX9R6?ref=ppx_yo2ov_dt_b_product_details&th=1 (12v 1A version)

220v Relay: https://www.amazon.com/dp/B07QXXM1RV?ref=ppx_yo2ov_dt_b_product_details&th=1 (12v Version)

Latching Relay: https://www.amazon.com/gp/product/B07RN5KLMF/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1 (I used this in another project that was in place for a few months without issue, re-using here.)

Switch: https://www.amazon.com/dp/B07KNNXLLH?ref=ppx_yo2ov_dt_b_product_details&th=1

I'm not sure how to troubleshoot this at this point. I've got a multi meter but not really anything more advanced that that.

Thanks for any suggestions!

Edit: As requested, I've simplified the schematic greatly. I made the latching relay more of a black box and separated the the momentary switches. The LEDs on the schematic are built into the switch.

The latching relay, is an board with other components that was premade. It takes 3 inputs, 12v+, ground, and the input. When the input is pulsed to ground, the relay changes state. When it is pulsed again, it changes state. The relay has a standard single input and 2 outputs (NO, NC.)

Prior to full assembly, I tested everything after the 220vAC-12vDC power supply without a load. I simulated the power supply with a bench 12v power supply and everything functioned as expected. The latching relay cycled with each press and the 220v relay coil followed.

  • \$\begingroup\$ If you draw the schematic using the version of circuitlab on this site (click the circuit button in the question editor), you can save it in an editable form. \$\endgroup\$
    – Hearth
    Commented May 8, 2022 at 15:41
  • \$\begingroup\$ All these lines confuse me please redraw a schematric much more readable. \$\endgroup\$
    – Jun Seo-He
    Commented May 8, 2022 at 15:56
  • \$\begingroup\$ Please do try to draw the actual way you wired things, not the way you think you're supposed to wire them. If you are using the built-in schematic tool then maybe you can draw an extra coil (is it the kind of latching relay that has two coils?) and a box around the whole thing. \$\endgroup\$ Commented May 8, 2022 at 16:23
  • \$\begingroup\$ Right now the schematic shows the "latching relay" is always on. \$\endgroup\$ Commented May 8, 2022 at 16:26
  • \$\begingroup\$ I have a concern about the latching relay, how does it work? It’s been implemented with a standard relay and some additional components - does it have separate on and off inputs? Or does it require polarity reversal? Or is it magical and simply turns on and off with successive pulses on a single input line? I would cut the 220V stuff out of the loop for now and do some experiments with the latching relay until it’s well understood. \$\endgroup\$
    – Bryan
    Commented May 8, 2022 at 17:18

2 Answers 2


Here's a simple solution using only two SPDT toggle switches.

enter image description here

  • \$\begingroup\$ Except that require doing all the wiring in 220V. Hmm, you could use bog-standard, approved AC mains wiring, switches and enclosures for that... that might be a lot safer than Chinese power supplies and relays. \$\endgroup\$ Commented May 9, 2022 at 4:29
  • \$\begingroup\$ The pump is for a pool and the boxes are all near water so I prefer to keep it at 12v for the switches. \$\endgroup\$
    – ecornwell
    Commented May 9, 2022 at 11:59

Turns out all I needed was a flyback diode on the 220v relay coil. I put at 1N4001 across the coil and so far, it's worked the first time every time I've tested!

  • \$\begingroup\$ I'm having a similar problem to yours - in a much simpler circuit. I'm using a small Panasonic latching relay (P/N: DSP1-L2-DC5V-F) to switch power to a Raspberry Pi ON & OFF. These things worked fine when I first bought them, but they seem to be stuck in one position now. I tried the flyback diode, but it didn't help. Driving me crazy. \$\endgroup\$
    – Seamus
    Commented 11 hours ago

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