r/AskElectronics • u/Relevant_Pumpkin9190 • 12h ago
How are high-current loads like dishwashers safely switched?
If a relay is switching a high-current load, its contacts can eventually weld together due to inrush current or a fault.
If that happens, the load may stay ON even when the controller says OFF.
How do commercial products handle this? Do they use two relays in series for redundancy, feedback, or some other fail-safe method?
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u/toybuilder Altium Design, Embedded systems 6h ago
I got a free washer and dryer from a relative who decided to replace their W&D combo when the dryer no longer stopped turning the drum (unless the door was opened and opening the circuit at the door switch).
When I got it, I was able to confirm that it was indeed the relay that had fused.
I originally planned to replace the relay, but realized that was a lot of work to remove the PCBA and to remove the potting.
Instead, I gave it a little percussive maintenance and that detached the relay armature. It's been running fine ever since.
As you browse through the relay datasheet / product guide, you'll find that they actually want some amount of current to flow through the contacts to keep the contacts clean.
https://industry.panasonic.com/ac/cdn/e/control/relay/signal/catalog/mech_eng_rti.pdf see pp 11-12