Garage Door Safety Beam

Tbone95 wrote: steve(ill) wrote: Tbone, i dont thing you can " wire around it".... everyone just tapes them looking at each other...... If one goes BAD, i think you are screwed.. Thanks Steve, I figured as much. As I mentioned, I found a broken wire and everything is working now, but while my thinking was getting ahead of my doing I was wondering if they could just be eliminated.

I would have to study a schematic but there has to be a way to wire around it. It is simply sending a go/no go voltage.

It's a pulse transmit/receive signal train.  If the transmitter doesn't talk to the operator in the proper way, you won't get a 'clear to operate' signal.

It's easier to open up the operator, yank the controller, and put in a simpler controller.

The operator runs on three signals... first is the 'command to run', the second is the 'direction to run' switch (either up or down), the last is 'excess load', which is a spring operated switch.

The Command To Run is a simple momentary.  The Direction To Run is a two position toggle switch tripped by mechanical piece on the operator's mechanism (chain, gear, etc)... it's either in the UP, or DOWN position.  It serves two functions... first, is to allow operating in one direction, the other is to STOP it when running to the limit of travel. If the machine is running in the UP direction, and the direction switch is tripped to the DOWN position, the operator stops.

It's not a complicated machine, they just added complicated hardware to prevent it from being modified.

When you press the button, the command-to-run signal energizes.  The 'direction' setting engages either one wire (to go one direction) or the other wire (to go the other direction) for operating the motor.  In old machines, this is nothing more than a 24v relay with two sets of contacts... one of which is tied to it's own coil to serve as a 'holding' contact.  Press the button, the relay stays closed until power to the coil is cut off.  The other sends power to the direction relay... whose two outputs (up and down) are connected to the motor's up direction winding, and down direction winding.

The motor starts in the direction identified... and it continues to run until the operator's limit switch contacts the 'direction' switch... which flips the DIRECTION switch... causing the motor to stop... as the motor direction switch has a pair of contacts in it that the HOLDING contact is looped through.

The last circuit element is the 'excess load' switch... which is nothing more than a microswitch depressed by a slider that the door operator works against (like, a chain tensioner, or the motor bracket) such that when an excessive load (in either direction) occurs, the tensioner or bracket shifts, causing the switch contacts to open.  They're in series with the COMMAND TO RUN relay's holding coil.  Put it in an 'excess load' state, and the relay just shuts off.

ANY door operator can be gutted of it's 'excess technology', and fitted up to operate in a realistic way.

Defeating the photobeam is more complicated, because the door operator's 'excess technology' is there to make it so you cannot easily 'defeat' it with anything other than a toilet paper tube and some duct tape.

The whole 'door beam' thing came as a result of 'supposition' that a child or pet could get injured or killed by a closing door.  In reality, this never actually happened, because part of setting up the door, is adjusting the opening and closing forces... that 'excess force' switch has to be dialed up enough to lift the door (the counterweights and springs need to be set up right to make it work, right?), so the actual opening and closing forces are very low.  In reality, a person can place their foot under the door, and it senses and reverses automatically.

In reality, the danger part of overhead door operators, isn't the operator, it's the door.  Specifically, the weight fo the door, and the countersprings used to counteract the door's weight.  Injuries from overhead doors come in three flavors:

1) Countersprings exploding on fatigue failure... most of the time this happens when nobody is around

2) People injured while adjusting overhead door countersprings, frequently springs that fail WHILE they're adjusting them...

3) Doors with failed countersprings FALLING on people.

Notice that NONE of these problems can be solved by the presence of a 'safety beam'.

Most of the problems with the Safety Beam come from the door NOT closing... including freezing the home, home invasion, and theft.   The door doesn't close because the beam prevents it from allowing the door to close.

There's four categories of beam failure-

Obstruction (dust, dirt, leaves and cobwebs, frost, snow, and ice)

Electrical failure (broken wiring)

Beam system failure (transmitter or receiver going bad)

Jamming (headlights, streetlights, or sunlight glare overpowering the beam).

Notice that last one?  If I wanted to break into someone's home, I'd get a high-powered flashlight or laser pointer, set it up in a good position to glare that beam receiver, and when they went to close the overhead door, I'd wait 'till the door was almost all the way down, then I'd hit the flashlight (glare the beam) to reverse the door AFTER they'd walked into their house.  Now the door is open, the bad guys can walk right in.

The beam is more of a danger than a protector.

As usual, Dave does his superb explanation of how things work. Thank you

DaveKamp wrote: It's a pulse transmit/receive signal train.  If the transmitter doesn't talk to the operator in the proper way, you won't get a 'clear to operate' signal...

Yup. Ultimately a Go/No Go after all of the pulses, frequencies, etc.

When I was in the Marines a half-century ago I was an avionics technician (COMMNAV). The IFF systems we worked on used a complex combination of frequencies/pulses to code the signals, ultimately to (I)dentify aircraft as (F)riend or (F)oe.