On 2/6/2016 1:33 PM, Jeff Wisnia wrote:
Don Y wrote:
On 2/6/2016 10:51 AM, Jeff Wisnia wrote:
That photoelectric stuff wasn't around when I installed the original
openers,
so I never really had any experience with it and didn't think of it at
first as
being the cause of the door reversing near fully closed. I know better
now.

IME, the photocells aren't worth their cost. They really only detect
things
that are ON the garage floor IN the path of the beam.

E.g., a kids wagon or bicycle typically won't trip the detector (the light
shines under or through). The same is true of vehicles (unless their front
or rear axles are in the path.

Openers that sense closing force (reversing when the feel "resistance")
also have too heavy of a hand in sensing (i.e., they'd crease the hood
of a vehicle parked beneath it). The door mechanism would have to be
critically damped to make them practical (at very low forces).

I agree with everything you say Don, and I am certainly aware that a lot of
those photoelectric sensors end up being mounted on the garage ceiling.

Probably a lot of them are up there because the homeowner who installed the
opener was too lazy to string and fasten the leads from the opener's location
to the both sides of the bottom of the door frame and sometimes might also
have to add a couple of pieces of wood to mount the units on so they were
located properly. (Like I had to.)

Ditto. Despite the fact that the included "brackets" SUGGESTED they should
just clip onto the door rails! (didn't fit)

But, since my luck is so bad that if someone left me a cemetery in their will,
people would stop dying, I just didn't want to risk the remote possibility that
someone would get seriously injured in a freak accident being smashed by the
door while it was closing and I'd get nailed for deliberately ignoring the
installation instructions. So, I installed them "the right way" and will put up
with whatever minor annoyances they may cause me in the future.

I installed them on our opener as well. I'm just commenting that they
(so far) have been more of a nuisance than a help.

Garage door has "stiffener ribs" that protrude about 3" into the garage from
the plane of the door. Not used to the "fit" of the new car in the garage,
yet, so always fear I've not BACKED IN (SWMBO doesn't like backing OUT!)
far enough to clear those "ribs". Each time I close the door I half expect
to hear them slap the front of the car as the door comes down (the photocell
doing nothing to prevent this!)

As you said, anything you've LEFT (or that has shifted position) in the path
causes the opener to complain. Last time, it was the rope for the cutting
blade on the pole saw that had dropped into the path. Of course, doesn't
cause a problem when you *open* the door. So, you're a bit surprised when
the door decides not to *close*! ("Huh? It opened just a minute ago;
why isn't it CLOSING, now??")

Also, it appears to "see" more than just the direct line between emitter
and detector. When I command the door closed and then try to run OUT
under the closing door -- taking care to "step over" the light path -- it
often "sees me" and reverses, even though I KNOW that I haven't broken
the light path.

I have issues with "safety devices" that have (significant) limitations.
E.g., the "cross traffic alert" on the car (tells you when other cars
are approaching from either side as you are backing out) sometimes sees
pedestrians; sometimes not; usually sees oncoming cars; sometimes not;
etc. I.e., it's not something that you can RELY upon.

It would be like walking with crutches -- that *sometimes* collapse under
your weight! :-/