Does active braking hold a load in the air, can it replace a mechanical brake?
No. Electrical braking produces torque only while there is movement; at standstill the holding torque is zero. A load left in the air needs a mechanical brake.
No. Electrical braking produces a counter-torque only while there is movement; when the motor stops the back-EMF is zero and no holding torque is left. Beyond that, the protection disappears entirely when the supply is cut. In every application where the load hangs in the air, a mechanical brake or a self-locking transmission is mandatory.
The first limit: braking torque arises from speed
The physical limit of electrical braking is this: the counter-torque arises from the back-EMF generated by the motor turning. When the motor stops, the back-EMF falls to zero and the braking torque goes to zero with it. If the load starts sliding down under gravity, the motor starts turning again and only then does some resistance form; that is not controlled holding but a sliding descent. Balance is only reached when the braking torque produced equals the load torque, which means the heavier the load, the faster the slide.
The second limit: dependence on energy
In the event of a blown fuse, a broken cable, a battery isolator opening or a driver failure, the electrical brake is completely out of action. A safety function has to be designed so that it engages by itself when the energy is cut; spring-applied, electrically released mechanical brakes work on this principle. Auditing whether the arrangement is right is easy too: cut the energy while the load is in the air, and if nothing moves the design is correct.
What each method provides
| Method | What it provides | Does it hold at standstill |
|---|---|---|
| Coasting | The motor is left to the load, inertia carries it on | No |
| Dynamic braking | Shortens the stopping distance | No |
| Current-threshold stop | Detects end of travel and overload | No |
| Electromagnetic mechanical brake | Closes when there is no energy | Yes |
What the first three rows of the table have in common is that they need both energy and movement in order to work; only the last row does its job in the absence of energy. A safety arrangement always rests on that last row, and the others are there for comfort and mechanical life.
The correct arrangement for lifting and platform applications
- The load is held by a mechanical brake or a self-locking transmission (worm gear, screw actuator).
- The driver's current-threshold stop function (AntiSwitch on the KS250 and PT500) is for end of travel and overload, not for holding.
- The electrical brake is used only to shorten the stopping distance.
- In hydraulic lifting the holding duty belongs to the load holding valve, and the valve is mounted on the cylinder port.
During braking the energy the motor produces returns to the supply line and raises the voltage. That is one of the limits of electrical braking in its own right and not an answer to the holding problem; with heavy loads the rising voltage can also strain the driver's tolerance.
Where electrical braking is sufficient
The dividing line is whether gravity keeps the movement going. On a horizontal sliding door, a conveyor or a rotary table there is no force pulling the load down once it has stopped; there, electrical braking is meaningful on its own for shortening the stopping distance. If the load hangs on a vertical or inclined axis the equation changes and the holding duty must pass to a mechanical element. The question to ask when deciding is a single sentence: when the energy is cut, does this load move on its own?
What to do
Plan the mechanical holding as a separate element in every arrangement where the load can stay in the air, test it after installation by cutting the energy, and write that test into the periodic maintenance list. The brake lining and the spring weaken over time; a test that passes on day one may not pass in the second year. Electrical braking must never be relied on for any load a person could be underneath.
The full topic: DC Motor Driver Selection Guide