Comment by mikeayles
8 hours ago
Most washing machines use a wax motor to lock the door, it heats up wax to cause it to expand when it melts, which drives a pin. They're fairly failsafe as if you kill power, they will open no matter what.
Latching relays/(technically solenoid) could be driven on/off fast, the downside is in a power cut or an emergency, the relay wouldn't release unless specifically driven so.
So the third option is a momentary solenoid, which would need to be powered the whole time the door is shut, and they require a surprisingly significant amount of power. Typically 10-20w. Negligible when it compares to the KW+ heating elements, but they do add up for the energy ratings..
Fwiw, I currently have a haier, which does have one of the second options, and opens immediately after a wash and it's amazing. Can't go back.
But, wax motors continue to be used because they're just the right tool for the job.
You can still buy machines without the lid lock. They use an alternative design that can stop motion quickly enough to meet safety standards. I can open the lid on my washer in the middle of a heavy spin cycle at max RPM if I want to, but it will brake aggressively and come to a halt within 1-2 seconds. Being able to add laundry mid-cycle without asking permission from the computer is really nice.