"Stephen" wrote in message
...
Hello,

I bought a roller door from a well known auction site ;(

The problem is that the box of electronics controlling it has got two
relays. I imagine one for up and one for down. The "up" relay is
sticking so that the door will not open. I have opened the box of
electronics and given the relay a tap and it is working for now but I
expect it to stick again soon. How can I prevent it from sticking in
the future? Is there anything I can do? I guess I really need to get
out the soldering iron and replace it before it fails completely.


Now that you have freed it off, it may not ever stick again. If it had been
a small carbon build up over the contacts, the slap you gave it might have
been enough to clean it. Daily operation might be enough to keep it clean.
But you'd have to tell us what the contacts on the relay look like. Are
they blackened and damaged? Looking inside the relay, does it look like it
really needs replaced?



Does anyone know the schematic for these boxes of tricks? I presume
the relays isolate the electronics from the motor? Is the switch side
of the relay connected to the mains on one side and the motor on the
other? Is the relay output open circuit when he door is stationary? If
so I was wondering whether I could put a switch in parallel with the
relay so that I have an emergency override? Is this possible?


What voltage doe the door run on? Have you connected to mains voltage
(240Vac)? What voltage does it say on the side of the relay covers or other
components? Did you get a transformer with the door, or did you have to
supply one yourself?

A separate switch as an override for what? Why don't you remove the
electronic controller and install two switches? One for open and one for
close.



My worry is that if the relay output is connected to ground when
stationary, I don't want to blow a fuse when I switch the override!


If this is a mains voltage (240Vac) system, I don't think any part of the
control system will deliberately connect to an safety earth bond. That
would be really silly.



I notice there is a spark when the relays open. I'm not sure whether
that's the reverse emf in the coil or just the mains jumping the
contacts as they separate. Possibly this is welding the relay stuck.
Do you think I should add diodes?


A relay will arc a little as the contacts make and break. It is why the
relay may have stuck in the first place, because the arc can cause a carbon
deposit to build on the face of the studs.

The controller most likely contains diode protection against field collapse,
so it shouldn't need any more. Definitely not across the mains contacts.



The box is branded Nico IIRC.

Thanks,
Stephen.


Best to find out who made the controller and search their website for a
manual on it. It should give you a better idea of what it can and can't do.

Good luck with it.