Latching Circuit to Stop 120V Power to Washing Machine

Thread Starter

drnate

Joined Apr 28, 2023
5
Hello! I started this thread: https://forum.allaboutcircuits.com/...-laundry-machine-shutoff-switch-relay.193432/ a little over a year ago. We are finally getting back to work on it.

To recap - our washing machine drain line plugs from time to time and floods the room. My son and I designed a control circuit that would sense the rising level in the pipe via a float and switch and shut the power off to the washing machine before the machine empties itself onto my floor.

In the original thread, I was asked to post diagrams for critique, so here they are. I am using an 8" x 8" Square PVC control box attached to a PVC receptacle box. The control box houses a Circon CFM40T-02 Switching Power Supply, our circuit board with a SN74LS02 IC and an Altech Corp 8905.2 relay. We have set the IC up as an SR Latch, which activates the relay, opening the 120 volt stopping the washing machine when the float switch closes. On the bottom of the box is a fused Power Inlet that will plug into the GFCI wall receptacle to provide power to the electronics and the washing machine. Indicator lights, an audible alarm, and the reset button and a reset button will be on the top.

My Questions:
1) I plan to put a 15 Amp Fuse in the power inlet. Is that adequate for the entire unit, or should I have something smaller on the circuit board?
2) I think I need to use the NC side of the relay, not the NO side, can someone confirm?
3) Do I need to / is there a way to ground the DC side of the Power Supply?
4) The CFM40T-02 (Datasheet Here) uses "industry standard" pinout that does appear to have a connection for 14 AWG Copper wire. Is there a piece I am missing?
5) The original feedback suggested a ruggedized design - I think this fits the bill, but again, I am open to feedback.
6) Anything I may be forgetting....
 

Attachments

MisterBill2

Joined Jan 23, 2018
18,934
First, unless the water level sensor uses the water as part of the sensing system, there would be no reason to connect any part of the isolated output of the power supply to a safety ground connection. Second, your mains outlet is already protected by a fuse at the distribution panel. Given that you appear to be assembling a sturdy system that will not have loose parts wandering around, you do not need to add another fuse. The power supply is not providing 15 amps of power, but rather just a few watts for the relay and the electronics board. So the power supply can use much thinner wire. AND it will be much easier working if you use stranded wire inside the box, unless you want to use something like #20 size wire . The wiring diagram does not provide enough detail to evaluate the design so I can't comment on that part.
 

Thread Starter

drnate

Joined Apr 28, 2023
5
Thank you, MisterBill2, for the prompt and polite response!
So the power supply can use much thinner wire.
Can I just solder the thinner wires to the mains inlet, together with the wires taking the mains over to the washing machine? or is there an adapter I should be looking for?
 

MisterBill2

Joined Jan 23, 2018
18,934
Yes, it appears. That is, if there is space for both the washer's current carrying wires and the wires for the power supply power. That is often done, using the inlet terminal points for more than one wire.
 

Thread Starter

drnate

Joined Apr 28, 2023
5
Thank you again MisterBill2!
In looking at mounted buttons and mounted LEDs, Amazon is quite a bit cheaper (Here) than Mouser (Here). Am I missing something on Mouser that might be less expensive, or is the expense worth the quality?
 

MisterBill2

Joined Jan 23, 2018
18,934
Quality varies a whole lot on amazon, some very good and some rather not so good. Mouser offerings are more consistently exactly as described, with consistent good quality. For my own use Amazon would be worth a try on less expensive items, while for production items it is important to be able to verify in advance of ordering.
 
Top