Had to pick between a solid state relay and a contactor for a 30 year old Otis controller last Tuesday

I went with the solid state relay since the building manager wanted quieter operation, and it passed the test run but now the door operator is acting sluggish - anyone run into voltage drop issues with SSR swaps on old gear?

3 comments

3 Comments

the_grace6d ago

...and that's exactly the kind of thing that got me on a 3 day wild goose chase last spring with a similar setup. I swapped in a little Omron solid state relay on an old elevator panel, everything ran quiet for about an hour, then the door motor started dragging like it was running on a dying 9 volt battery. Turns out the SSR was pulling just enough voltage off the line that the old controller couldn't keep its logic happy, so the door operator got starved for power every time it tried to move. I ended up having to put a small heat sink on the relay and add a separate 24vdc supply just for the door circuit to stop it from acting up.

seanjackson6d ago

Yeah man, that voltage drop issue is a sneaky one. Once you start swapping in solid state stuff on older gear, you're basically playing detective with ghost loads. A separate supply is almost always the fix for those old panels, they just can't handle modern relays without some help.

the_elizabeth6d ago

The same kind of ghost load thing happens with smart home switches on old wiring, where that little standby power drain messes with dimmers and buzzes lights constantly. @the_grace's elevator story is spot on, that voltage sag from modern parts starving old logic is a pattern I keep seeing across all kinds of gear, not just industrial stuff. It's like every new component assumes the power is perfect, but older systems just weren't built for that kind of draw.