On a horizontal machine, a sloppy brake handoff costs you a lurch. On a vertical one it costs you the load. Gravity acts straight down the direction of motion on a hoist, and it never stops pulling, so the instant the brake releases, the drive has to already be holding the full weight of the load or it falls. This is the article the horizontal brake note promised, and it is a different animal, because holding a suspended load at the moment of release is the hardest thing a drive and a brake do together.
The whole game is torque at zero speed, delivered before the brake ever opens and held until the brake is fully set. Getting that sequence right is a commissioning task and a safety task at once, and it lives in the VFD Commissioning Guide.
The Problem Is Torque at Zero Speed
To hold a hanging load with the brake open, the motor has to make full torque while the shaft is not turning. A standard volts per hertz drive struggles here, because at zero frequency it makes almost no voltage and therefore almost no torque. That is the same reason a self powered motor brake will not release on a drive, and it is why a hoist is not a job for a warmed over fan configuration.
There are two honest ways to make torque at zero speed. The robust one is closed loop, an encoder on the motor so the drive knows shaft position and can hold full torque at a true standstill. The other is an open loop trick that works within limits, and it is worth understanding because plenty of hoists run it.
The Open Loop Holding Frequency
On volts per hertz, you cannot make torque at a true zero frequency, so you do not try. Instead the drive outputs a small holding frequency, and because the shaft is still held by the brake at zero speed, that frequency shows up entirely as slip, and slip is what makes torque in an induction motor. Choose that frequency so the slip torque equals the static torque of the load, and the motor is now carrying the load through the brake before the brake ever opens.
That number is what a crane program calls the brake release start frequency. Set it correctly and the load does not move when the brake releases, because the motor was already holding it. Set it too low and the load sags or rolls back at release. It is the open loop version of pre torque, and it is a real tool, but it has a real limitation worth stating plainly. It is set for a known load and it has no feedback, so a load heavier than expected, or a stall, is not detected, it just slips. When the load varies or the consequences are severe, closed loop with torque proving is what you graduate to.
The Sequence, Start to Stop
Brand does not matter here. Every crane and hoist program, from KEB to ABB to the rest, implements the same sequence, usually exposed as a handful of programmable timers. Walking it once makes the whole thing click.
At start, the run command comes in and the drive first spends a premagnetizing time building flux in the motor, because a motor with no flux makes no torque no matter what else you do. With flux established, the drive ramps its output to the holding frequency and develops the torque to carry the load at standstill. Only now does it energize the brake control relay, and the brake takes its own brake release time to physically pull open. Through that entire release time the motor is already holding the load, so nothing moves. Then the drive accelerates to the commanded speed.
At stop, the drive decelerates back down, not to zero, but to the brake engage start frequency, the holding frequency again, and it holds there. A brake engage delay time lets the load settle to a true steady state at that frequency, which matters because the motor may not have tracked the deceleration ramp exactly. Then the drive de-energizes the brake relay and the brake takes its brake engage closing time to physically clamp, and the drive holds the load at the holding frequency through that whole closing time. Only after the brake is fully set does the drive fade the motor current to zero and drop its modulation. The order never changes. Flux, then torque, then release. Settle, then set, then fade.
Set the Brake at Zero Speed, Not While Moving
One detail from that sequence carries more weight than it looks. The brake is engaged at zero speed, with the drive holding the load, not slammed on against a moving shaft. A spring set friction brake will stop a moving load, that is dynamic braking, but every time it does, it grinds a little material off the friction surface. Do it on every cycle and the brake wears, the holding torque fades, and one day it no longer holds the load it was sized for.
Let the drive stop the load and hold it, then set the brake at standstill, and the friction surface only ever clamps a load that is already stopped. That is static braking, and it is why a properly sequenced hoist brake lasts and an improperly sequenced one becomes a maintenance and safety item. Brake wear that traces back to dynamic engagement belongs in the VFD Maintenance and Reliability Guide.
Torque Proving and Rollback Prevention
Because a hoist gap drops a load, the good crane programs add checks around the handoff. Torque proving confirms, before the brake ever releases, that the drive can actually make the required torque and that current is present in all phases, so a miswired motor or an open phase keeps the brake set and faults instead of releasing into a load it cannot hold. Some programs add brake proving on the set side, testing the load against the brake before the drive lets go, and faulting if the brake slips.
These are not extras on a hoist. They are the difference between a controlled failure, where the brake stays set and the drive throws a fault, and an uncontrolled one, where the load moves. The selection of a drive and motor that can hold torque at zero speed and support these functions is a sizing decision, covered in the VFD Selection and Sizing Guide, and when rollback or a dropped load shows up as a symptom, the sequence is where it lives, per the VFD Troubleshooting Guide.
Why This Belongs in the Drive
You could build this sequence in a PLC outside the drive, timing the brake relay against the drive’s speed and torque with external logic. The reason to keep it inside the drive is that the drive already knows its flux, its torque, and its speed to the millisecond, and coordinating the brake against those signals through an external controller adds latency and parts that can drift out of step. Putting the brake control in the drive removes that external logic, often removes a PLC, and keeps the release and set locked to the torque the drive is actually making. The drive switches a low voltage control relay, and an external relay sized to the brake voltage does the actual switching of the brake coil, because the brake coil current and voltage are usually more than a control terminal should carry.
Setting It Up Safely
A dropped suspended load is a life safety event, so the hoist brake sequence earns more care than anything else on the machine. The rule is the same as the horizontal case, made unforgiving. The drive makes torque, then the brake releases. The brake sets at zero speed, then the drive fades out. On a hoist there is no margin in that order, because gravity is always waiting in the gap.
Hoist and crane control, closed loop torque at zero speed, torque proving, and brake sequencing get their full treatment in the VFD training program and in Before the First Fault. If you are commissioning a hoist, get the brake sequence right first and sign it off last.
Author: Dr. Carl Lee Tolbert, PhD, CMRP, Wayward Leaders LLC, waywardleaders.com
Frequently Asked Questions
Why does a hoist need special brake control?
On a hoist, gravity pulls the load down the direction of motion, so if the brake releases before the drive is holding the load, the load falls. The drive has to make full torque at zero speed and release the brake only after that torque is established, which generic drive control does not do. Crane and hoist firmware adds the sequencing, holding torque, and safety checks that close that gap.
How does a VFD hold a hanging load at zero speed?
Two ways. Closed loop control with an encoder lets the drive make full torque at a true standstill. Open loop volts per hertz cannot make torque at zero frequency, so the drive outputs a small holding frequency that produces enough slip torque to carry the static load, holding it before the brake ever opens.
What is the brake release start frequency?
It is the small output frequency a volts per hertz drive holds so the motor makes just enough torque, through slip, to carry the load at standstill before the brake releases. Set correctly, the load does not move when the brake opens. Set too low, the load sags or rolls back, so it has to be tuned to the actual load.
Why should the brake engage at zero speed?
Setting the brake while the shaft is still turning uses the friction surface as a stopping device, which grinds material off it every cycle and slowly reduces the holding torque. Letting the drive stop and hold the load, then setting the brake at standstill, means the friction surface only ever clamps a stopped load. That static engagement is what makes the brake last.
What is torque proving on a hoist drive?
Torque proving confirms the drive can actually produce the required torque, and that current is present in all phases, before it releases the brake. If the drive cannot make the torque, because of an open phase, a miswired motor, or an overload, it keeps the brake set and faults rather than releasing into a load it cannot hold. It turns a potential dropped load into a controlled fault.
Can I run a hoist with open loop volts per hertz control?
You can, using a holding frequency to make torque before release, and many hoists run this way. The limitation is that open loop has no feedback, so it is tuned for a known load and cannot detect a heavier load or a stall, it simply slips. When the load varies or the consequences of a slip are severe, closed loop control with torque proving is the safer choice.