I understand the basics of how a garage door works – the opener motor is assisted by the spring’s stored energy, otherwise the door would require a *much* larger motor to lift it.
But, some of these springs really look monstrous, and I’m wondering – how is their stored energy controlled? How do we ensure the spring releases just enough energy to assist the motor, and doesn’t just launch the door into orbit?
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When they’re installed you have to manually wind them up to get the right tension (or with other styles, you manually shorten the cable between the door and the spring). The more you wind them the more of the weight of the door they take up.
Think of them like a big sandbag on the other end of a pulley. If you put 100 pounds of sand in with a 110 pound door then the effective weight of the door is 10 pounds and no amount of releasing energy will cause the sandbag to yeet the door.
The springs are tightened just enough that their tension overcomes the weight of the door. The door should stop at around 2ft from the floor with the motor disconnected, if I recall. The spring tension is held by setscrews on the shaft above the door.
We replaced our old wooden door with a newer fiberglass one and had to adjust the spring tension since the new door was lighter.
You wind them by hand and test with the motor to see if you need more or less spring assist. I’ve also seen it done to where you wind them by hand until the door stays where ever you put it when the motor is disengaged.
The spring offsets the weight of the door. If the spring had enough tension to move the door on its own, the door wouldn’t have closed in the first place. So it’s controlled by the fact that it’s attached to a heavy door that can only move along a track.
That’s not exactly how garage doors work.
The springs are there to completely counterbalance the door. The length of the spring, the inner diameter of the spring, and the gauge of the wire are all very intentionally chosen based on the amount of lift of the door, the height, width, and weight of the door. Even the size and shape of the drums (the things the cable wraps around) is taken into account.
What you mentioned, a door just taking off, is described in the industry as “too hot”. A door that won’t lift, or wants to come back down is described as “too heavy”. And a door that, without an operator on it, is released at any point in the normal travel without moving (too much) is considered well balanced.
Just as the springs lift the door (by wrapping the cable around the drums), the weight of the door keeps the springs in check.
***Balance.***
And then they get old and while under tension opening they suddenly explode like a nuclear bomb and almost kill you.
Then you go try to open your door without them and you can’t because your door weighs like 400 pounds
Ask me how I know….
Garage springs and truck coilovers. 2 things I refuse to mess with myself and pay someone else. Had a buddy help me do some work on the truck and he used a Harbor Freight clamp, that thing exploded like a bomb and launched itself across the garage missing me by inches. I’m out on all that.
Wow, so my garage door is basically a giant teeter-totter with a sandbag on the other end…I feel smarter already.
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