The setback of a gate opener is the geometric relation between the hinge of the gate and the rear pivot point of a gate opener. It seems simple but this is one of the most commonly overlooked aspects of installing a gate opener and most common causes of issues with a gate opener working consistently.
Why is this commonly not correct? It is many times due to an obstacle. Lets say you have a post that is next to a fence. The manual calls for placing the rear pivot point 9″ x 9″ away from the hinge. This means you measure back away from the hinge in toward the property 9″ and then make a right hand turn and measure back behind the post 9″. But in your case you don’t have that much room, your post is only a 4″ x 4″ post and the fence is right next to the post and running parallel to the driveway. You can only do 3″ of the second measurement before you run out of room to fit the gate opener when the gate is open. On the surface it would seem the individual installing would stop there and not mount the gate opener because it wont work. But what happens in many cases it they attempt this alternate setback and find that the gate opener piston can still move the gate fully open and closed! This makes them happy, they leave it with this wrong setback and move on.
Why did it work? It worked because the geometry was less than what was being called for. The fixed variable in the equation is the length of the piston of the gate opener that moves in and out (called stroke length). When you move the rear pivot point of the gate opener closer to the hinge of the gate than the manufacturer has calculated as ideal; every inch the piston moves will move the gate a larger degree of its swing. This will have two results: the gate opener will move from closed to open faster and the gate opener will also have less leverage on the gate. If the geometry was greater than what was being called for in the manual, the gate would move less per inch of the piston movement. What you would see in that case is the gate opener would run out of piston before the gate is open to a full 90 degrees. So in the case of the setback is too far from the hinge of the gate most people figure out that it is not going to work from trial and error.
If the wrong setback gets the gate from closed to open and also moves the gate open faster, why is this bad? There are a number of reasons:
1. Adjustment of limit switches. This is one part that may in a good way prevent you from making this mistake. During set up with many gate openers you must manually move limit switches into a position where the piston trips the limit switch during its travel back and forth. However some manufacturers isolate the switches toward the ends of the gate opener piston’s travel. So if your setback is off and the piston only retracts half way before the gate is fully open you may not be able to adjust the limit switch into a position where the piston has traveled far enough to trigger the limit switch.
2. Obstructions. This is very common. All gate openers have what is referred to as obstruction sensing. This is a function of the gate opener controls that senses a strain on the motor of the gate opener larger than there is supposed to be and then stops and reverses the motor. The idea is that if the gate hits something it will not crush the object. However with this wrong setback there are a couple of factors that can cause stress on the motor without an obstacle being present. One is less leverage on the gate. As we said above, when the rear pivot of the gate opener is closer to the hinge of the gate the leverage the gate opener has on the gate decreases. The force of trying to move the gate alone could be enough to trigger the obstruction sensing. A second is the speed of the gate. Since the gate will be moving at a much faster speed the strain of controlling mass in motion can play heavily on the strain of the motor. Your gate could be light and swinging very easily, but when the gate opener starts the gate in motion the momentum can cause a whipping action. When the gate whips the motor will strain to control this and it will cause an obstruction. Lastly, it may get through normal usage fine but the obstructions come into play when there are adverse conditions. When it is raining or cold the gate has more resistance. These are the exact times you want your gate opener to work correctly so you don’t have to get out of your car. But if your setback is off and your gate has less leverage these are the exact times you are setting the gate opener up to fail in.
3. Circuitry damage: If your setback is off you should actually hope for the above, an obstruction. Sometimes you may not get this constantly depending on the sensitivity levels. However the added heat from the lack of leverage is not good for the control board of the gate opener. It is similar to driving your car constantly at 5000 RPMs. You are putting strain on the system and decreasing the life of the gate opener. Most manufacturers are wise to what components will burn up in this example and will not warranty the control board.
What is the ideal setback for a gate opener? This is what they have already calculated in the manuals of the gate opener however here is an explanation of it. Ideally you want to utilize the entire stroke length of the gate opener piston when moving the gate from the closed to open position. This will move the gate at the speed the manufacturer has intended. This will give the maximum amount of leverage on the gate. This will get your gate open to the degree you want. You may notice some manufacturers have a few options for setbacks; for example they may have one for 90 degrees and another for 110 degrees. Use the one you wish to have the gate open to. Although the 110 degree setback will open the gate the 90 degrees, you are not using the ideal setback and you are leaving leverage and control on the table.