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Looking for a budget latching relay which needs manually resetting once triggered

tl;dr version:

I'm looking for a mains-voltage simple latching relay which will simply open a circuit as soon as it's triggered, and then stay latched open until reset either physically, or by some kind of push-button trigger.

Without going into the tedious details*, I need to cut out a 300 watt inductive mains-powered water pump if it has been running for more than 10 minutes. 

After a few phone calls to RS and others, it became clear I needed to make this out of two components, delayed-on timer and a latching relay. I found the timer at

Now I just need the latching relay. So many choices, mind-boggled, not quite sure which one.

I'm in the UK, and this is a home hobby project, so suggestions of "just simply use this £395 PCL" wouldn't be so helpful!

And optionally, I'm also looking for a cheap mains-voltage buzzer which will just go "beep beep beep" when energized. Again, struggling to find that.

Thank you.

(*OK, if you REALLY want to know the story behind why I want to do this, read this. It gets tedious...



0 Votes


March 7, 2019 11:45

Generally, you can get a cheapish "smart relay" which is fully programmable and can be used for way more than what you want for the same cost as a timer and relay. This would be the best option if you want to go for "1 part." It has its own power supply, timers, relays the lot. As it can do so much more than you want you can also play around with it to use on extra projects.
The smart relays are relatively simple to program on the keypad and are reliable to an industrial standard.
If cheap is your main goal, you can get an Arduino board and a relay for a couple of bucks on e-bay. Then you've got to put it all together, program it, get a power supply etc.

0 Votes

October 3, 2018 07:37

Hi there,
I had a look at the story on diynot and I honestly think your best solution(s) were provided on the plumbing thread.
If robustness to failure is your main intent, then the suggestion to [firstly increase the size of your overflow pipe and] use two series-wired float switches – or a lower switch to turn the pump on and upper switch (backed up with a ball-cock if you really want security) to turn off the pump is the way to go. These both have the benefit of being simple. What you are proposing, although a bit ‘techie’ is much more expensive to implement and statistically likely to fail a long time before the simple solution.
I tell you this as an electronics engineer who loves electronics but also has a strong appreciation of how (complex) electronics fail in the field.

0 Votes

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