Hello!

This is more hobby than anything else - we are not professional engineers (so if I need to find a different forum, please let me know - and offer a suggestion, please).

My son and I are exploring electronic circuits by trying to design something useful. Our washing machine floods occasionally. I see a lot of leak detector wet sensor shut offs on Amazon. Our design makes use of a float in the drain pipe to shut the machine off before it starts pouring water onto the floor.

We have most of the it figured out. I'm just not what kind of a relay we need to get the 5 volts from the logic gates to operate the 125 volt 15 amp circuit the washing machine uses. The DR22 Series Solid State Relay (https://www.mouser.com/datasheet/2/...es_ac_lp_din_rail_mount_ssr_datas-2930274.pdf) seems like it would fit the bill. It is quite a bit bigger than the entire units I see on Amazon. Is there something smaller / cheaper that would do the job for us?

Thank you for your time.
drnate

 

Where is the 5v derived from?
Is there any other voltage available from whatever the supply is?
Either AC or DC?

 

The Solid State Relay mentioned is quite a bit bigger, both because it can handle more current and because it is a better quality. And at least some of those SSR devices are made to operate with a 5 volt control signal.

 

You could go for something like this https://us.rs-online.com/product/carlo-gavazzi-inc-/rf1a23l25/70633550/ This SSR can handle up to 25A (with heatsink) and it is very small in size. My question to you is why did you opt for a solid state relay in this case? As I understand, the relay will only be activated in case of an overflow. So you frequency of switching is quite low.

 

It is quite a bit bigger than the entire units I see on Amazon. Is there something smaller / cheaper that would do the job for us?

As per the previous post (#4) , there are the smaller versions on Amazon also.


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Thank you for the robust discussion. My terminology may be a little off - so I'm going to take some space and explain my answers to your questions.

First, in response to the first question from MaxHeadRoom: Regarding your voltage question: The 5 Volts comes from this product from Amazon. The board can push 700mA. Right now, we are using a battery to power his circuit. I hope to eventually use a 9 volt Wall Power Adapter with a barrel plug on the circuit board. Other than the 120 volt AC for the washing machine (which we will have a fuse for), that is all we were planning. Now, we can certainly use a wall adapter with higher voltage and design a voltage divider into our DC circuit if we need to have other DC Voltages available. (Picture from Amazon)


In response to Demjas17: Regarding when the relay will be active: The DR relay I cited looks like it only lets power through when the control is active (I believe it is normally open). Is the one you listed also normally open? For some reason, I was thinking it would be safer to use a better quality relay if we need to use a normally open system. I don't have to use an SSR - The switching state would only change if the sensor is activated.

Some of the reviews of the cheaper products mention melting plastic - If I need to spend more money to keep everyone safe and not burn my house down, I'm good with that.

Thank you again for looking at this. Please let me know if I need to offer clarity on anything.

drnate

 

I wouldn't use a SSR for this project, and I sure as hell wouldn't get one from Amazon if I did.

If you use an SSR that means the relay must always be on during the wash cycle, and would require a huge heat sink. If failsafe is a concern, you can still use a mechanical relay. (failsafe in this context would be if the relay fails to operate)

If you use a mechanical relay, you can use the NC contacts and the relay requires no power during the wash cycle.

Then when your sensor detects a flood, the relay opens the connection. The circuit is very straight forward if the float is NO but would require another small relay or electronic circuit if NC. (NO = closed during flood)

The really critical part of this project will be interfacing the washer power cord with the sensor circuit, I would suggest constructing in such a way that the washer simply plugs into your device and requires no modifications to the washer wiring, meaning a rugged design using a proper enclosure and a standard outlet.

You also need to be very careful about what happens when the water activates the relay and the recedes, so I would also consider a way to latch the relay if a flood does occur, if your washer has electronic controls and won't start again after a power outage then this is not necessary.

The latch is simple using a DPDT relay.

Please be sure to post your design in full for critique before implementing.

 

If you use that 24 volt powered contactor to enable power to the washer, then the float switch, if i has contacts that open on rise, can simply open and release the contactor if the float rises. There is no need for any 5 volt circuitry.

But, given that overflow is not an intended part of the machine operation, I suggest a research project to discover the cause of the problem, and solve that.
Toward that end, I suggest an indicator light to alert you as to when the water valve is powered to open. That sort of valve is subject to being blocked into the flowing condition by even a small amount of dirt particles.