Hoist Regenerative Power: What a 5 Tonne Hoist Sends Back Up the Cable, 0.125 to 100 Ton

Written by Li Ming, Senior Applications Engineer at SIEC Cranes. Nov 6, 2026.

Every overhead crane has exactly one mechanism that can send power back up the cable, and it is the one bolted to the hook. A 5 tonne hoist lowering six metres at six metres a minute pushes roughly 4.2 kW back into the drive for the length of that descent. What happens next is a choice, not physics. Heat in a resistor, or electricity back into the plant. On that 5 tonne unit the choice is worth about USD 150 a year. On a 50 tonne crab it is worth USD 6,000.

The mechanics are simple and the electrics are not. A load coming down turns the motor into a generator, the generator charges a DC bus that has nowhere to put the charge, and something has to absorb it before the drive shuts itself down in mid air. Most of the arguments we have with buyers are about which of the three absorbers to pay for.

This is the hoist side of that argument. Not the whole crane. The hoist is the only motion where the energy is worth collecting, and it is also the only motion where getting it wrong drops a load.

Which part of a crane can actually give energy back?

Only the hoist, and the reason is arithmetic. Lowering a load releases stored potential energy, m times g times h, which is large and comes back on every single cycle. Stopping a moving bridge releases kinetic energy, half m v squared, which is small and happens once per traverse.

Put numbers on it. A 20 tonne bridge travelling at 40 m/min carries about 4.4 kJ of kinetic energy. Bringing it to rest recovers that, in theory, if you catch all of it. The same crane lowering 20 tonnes through 10 m releases 1,962 kJ. That is roughly 445 times more energy, in one motion, every time the hook goes down.

Motion	Energy available per event	Where it comes from	Worth collecting?
Hoist lowering, 20 t through 10 m	1,962 kJ (0.55 kWh)	Stored potential energy, recharged on every lift	Yes. This is the whole case for regeneration
Bridge travel, 20 t at 40 m/min, stopped	4.4 kJ (0.0012 kWh)	Kinetic energy of the moving mass	No. You will spend more on the drive than you recover
Trolley travel, 5 t at 20 m/min, stopped	0.28 kJ (0.00008 kWh)	Kinetic energy, and a lot of rolling friction	No. Friction eats most of it before the motor does
Slewing or jib rotation, stopped	Friction work only	Bearing and gear losses	No. There is no stored energy to release

So when a brochure says the crane is regenerative, ask which motion. If the answer is travel, the feature exists to reduce brake wear, not to recover energy, and the two are not the same purchase. We have seen quotes where the word appeared four times and the only thing that regenerated was the hoist.

How much energy is in one lowering cycle?

The formula is short: energy equals mass times gravity times height, and the electrical energy you can send back is that number multiplied by the efficiency of the gearbox, motor and drive, because every one of them takes a cut in the generating direction too. We use 0.85 for a worm or helical hoist with a modern drive.

For a 5 tonne hoist lowering 6 m: 5,000 kg times 9.81 times 6 m is 294 kJ, and at 0.85 that is 0.070 kWh of electricity. At USD 0.12 per kWh the cycle is worth 0.8 of one cent.

Capacity	Lowering height	Energy released	Electricity returned	Value at USD 0.12/kWh
0.5 t	3 m	14.7 kJ	0.0035 kWh	0.04 cents
1 t	3 m	29.4 kJ	0.0069 kWh	0.08 cents
2 t	4 m	78.5 kJ	0.0185 kWh	0.22 cents
5 t	6 m	294 kJ	0.070 kWh	0.8 cents
10 t	8 m	785 kJ	0.185 kWh	2.2 cents
20 t	10 m	1,962 kJ	0.463 kWh	5.6 cents
50 t	12 m	5,886 kJ	1.39 kWh	16.7 cents
100 t	15 m	14,715 kJ	3.47 kWh	41.7 cents

Those numbers are ours, calculated for this article, and they cross-check against published examples from the resistor industry. Cressall uses a lift with four people in it at 25 kJ and a 40 foot container lowered onto a ship at 2 MJ, which is the same order as our 20 tonne figure once you account for their 20 m drop and gravity rounded to 10. If your load is a 40 foot container going into a hold, one descent is 2 megajoules and the argument about recovery becomes a different conversation.

Where does that energy go if nothing collects it?

Four paths exist. They differ in what happens to the energy, in what the buyer pays, and in what fails first.

Configuration	Where the energy goes	What it costs	What fails first
Two-speed contactor hoist, no drive	Back into the plant through the contactor, uncontrolled	Cheapest. No drive, no resistor, no chopper	Brake linings and the contactor
VFD with brake chopper and resistor	Heat, outside the panel, 100 percent lost	Drive plus a resistor worth a few hundred dollars	Resistor terminals and the chopper transistor
VFD with regenerative front end	Back to the line at about 0.99 power factor	Drive premium, and usually a line reactor or filter drawing	The front end itself, if it is undersized for the duty
Shared DC bus with a second drive	Into whatever else is accelerating on the same bus	DC bus hardware and a coordinated drive group	The interlock, if one drive is isolated while the other runs

The fourth option is the one buyers ask about least and should ask about most. A twin-hoist crane, or a hoist and a long travel drive fed from one bus, can pass energy between them without any connection to the supply at all. That is the cheapest regenerative system there is, because the only hardware is the bus and the only design work is the interlock.

What happens inside the drive when the load comes down?

The motor generates, and because the drive's rectifier only conducts one way, the energy has nowhere to go except into the capacitors on the DC bus. Those capacitors are not a battery. Cressall puts their usable absorption at 3 to 5 percent of the regenerated power. On a 10 tonne hoist returning 11 kW that is 330 to 550 W, which delays the problem by a fraction of a second and then stops helping.

The bus voltage then climbs. On a 400 V drive the nominal DC level is 400 times the square root of two, so 566 V. Most drives switch the brake chopper on somewhere around 1.2 to 1.25 times nominal, which puts it at 680 to 710 V, and most trip on overvoltage around 790 to 800 V. Check your own manual, because these are family-specific, but the shape is the same everywhere: you have roughly 100 V of headroom between "start dumping energy" and "shut down in mid air".

DC bus state, 400 V class drive	Typical level	What is happening
Nominal, motor drawing power	566 V	Rectifier feeding the bus, capacitors charged to peak line voltage
Regeneration begins	570 to 620 V	Capacitors absorb 3 to 5 percent of the returned power and the bus starts to rise
Brake chopper switches on	680 to 710 V	IGBT connects the resistor across the bus and the voltage stops climbing
Resistor hot, chopper modulating	700 V plus or minus 10 V	Energy is being turned into heat and the descent is under control
Overvoltage trip	790 to 800 V	Drive disconnects, torque disappears, mechanical brake slams on

That last row is the one that matters commercially. When the drive trips, the load does not stop gently. The brake closes on a moving drum, the rope and the gearbox take the shock, and on a heavy hoist the whole runway feels it. This is why "just put a bigger drive on it" is bad advice and why the resistor is not an optional accessory on a hoist.

Why does a standard VFD trip on the first heavy lift?

Because a general purpose drive is designed for a load that pushes back a little, and a hoist pushes back a lot. One crane drive supplier states the case bluntly: put a standard VFD on a conveyor belt and it runs beautifully, put the same drive on a crane hoist and it will likely fault with an overvoltage error on its first heavy lift. Their explanation is the one above, in fewer words, and the consequence they name is exactly the one you would fear. When a VFD shuts down mid air the mechanical brake slams shut and the crane takes a mechanical shock.

Danfoss says the same thing from the other side. Without a brake resistor, the DC link voltage keeps rising until the drive disconnects itself for protection. Their design guide then carries a warning that should be read by anyone who has ever been told that overvoltage control will solve this. The overvoltage control function, which lets a drive ride through a rising bus by reducing output frequency, is disabled by default in their braking guide and is specifically marked as not to be enabled in hoisting applications, with personal injury and equipment damage named as the consequence.

Read that carefully, because it explains a failure mode nobody expects. Overvoltage control works by letting the motor run faster than commanded, which on a conveyor is harmless and on a hoist means the load descends faster than the operator asked. The drive survives. The load arrives early and hard.

Diagnosis is mostly about timing. A drive that trips at idle or at power up is a supply and sensing problem. A drive that trips only while lowering, or only while decelerating, is pointed straight at regeneration and the energy path. A drive that trips exactly at a brake transition is a sequencing problem and needs speed, torque and brake feedback on one time line before anybody replaces a part. Repeated resets destroy the evidence and in the worst case damage the chopper.

How big should the braking resistor be?

Two numbers, often confused. The ohmic value sets how much power flows at a given bus voltage, because power is voltage squared over resistance. The watt rating sets how much heat the resistor can shed continuously. One governs whether the drive trips, the other governs whether the resistor survives the shift.

The usual shortcut comes from the drive makers. Schneider's hoisting application note asks for a resistor rated at no less than 50 percent of motor power for vertical movements, and 25 percent for horizontal ones, with the ohmic value above the drive's published minimum and as close to it as possible. Danfoss gives a formula for the resistance that includes motor efficiency around 0.90 and drive efficiency around 0.98, and warns that a higher resistance reduces achievable braking torque until the drive trips on a DC link overvoltage instead.

That 50 percent rule is a torque rule, not a heat rule, and the difference matters when someone tries to save money. Here is what a typical hoist actually dissipates.

Hoist	Motor	Resistor per the 50 percent rule	Peak power actually returned	Average power over the shift
1 t chain, 8 m/min	1.5 kW	0.75 kW	1.11 kW	0.19 kW
2 t chain, 8 m/min	3 kW	1.5 kW	2.2 kW	0.67 kW
5 t wire rope, 6 m/min	7.5 kW	3.75 kW	4.17 kW	0.63 kW
10 t wire rope, 8 m/min	13 kW	6.5 kW	11.1 kW	1.67 kW
20 t double rail, 5 m/min	30 kW	15 kW	13.9 kW	5.2 kW
50 t crab, 4 m/min	55 kW	27.5 kW	27.8 kW	12.5 kW

The averages are ours, computed for a duty of 20 to 120 lowering cycles per hour depending on class, half of them loaded, and a 0.90 factor for what the front end actually accepts. Two things fall out of the table.

First, on everything under about 10 tonnes the resistor runs at a fifth of its rating or less. That is fine and it is why resistors are cheap. Second, on a 20 or 50 tonne machine the peak power returned is close to the motor rating itself, which is exactly why the 50 percent rule exists and why it stops being conservative at the top of the range. On the 50 tonne unit the resistor is specified at 27.5 kW and the machine returns 27.8 kW. There is no margin in that number at all, and there is nothing wrong with the rule. It assumes you brake at rated torque, not above it.

Where people get into trouble is the other direction. Sizing the resistor from the average, which looks diligent and costs less, gives you a resistor with the thermal mass of a coffee cup and a first shift that ends in a chopper failure. Fitting a lower resistance to "brake harder" is worse. Delta's hoist troubleshooting guidance is explicit that too low a resistance can overload the chopper, and that a cold resistance reading proves nothing about in-service energy transfer.

What does 400 degrees of resistor heat mean for the building?

Continuous lowering will take a dynamic braking resistor past 400 degrees Celsius, which is 750 Fahrenheit. That is not a fault. That is the product working. Which is why the same guidance says the resistor has to be mounted outside the electrical panel, in a ventilated stainless steel enclosure, away from anything that can burn.

The most useful case study we have found on this is ABB's work at New Zealand Steel, published in June 2026. Two 125 tonne casting bay gantry cranes move 80 tonne ladles of molten steel, and the plant runs about 670,000 tonnes a year, so a stopped casting machine is not a maintenance inconvenience. The old drive arrangement used eight rooftop brake resistor cabinets, connected by heavy cabling, to burn off the energy from every lowering cycle. In a dusty steel mill those resistors needed a monthly flush to stop accumulated dust from causing local overheating, and the flush meant technicians working at 23 metres in a restricted space.

Five regenerative drives replaced the whole arrangement. The eight cabinets and their cables came out, the monthly climb stopped, and the plant reported a 40 to 45 percent reduction in electricity consumption in the initial operating phase.

Two admissions about that number. It is the plant's own figure from early operation, not a controlled measurement, and it includes more than recovery of braking energy, because removing eight resistor cabinets from an electrical room also removes a large air conditioning load. But the direction is not in doubt, and the maintenance story is the part that convinces a plant manager. A resistor that needs dusting at height is a resistor that eventually catches fire.

When does regeneration pay for itself?

Here is the part where most of the marketing falls away. We took the same seven machines, applied a realistic duty for each, and priced the recovered energy at USD 0.12 per kWh. The regenerative premium is our own planning band for a front end rather than a resistor, from about USD 700 on a small chain hoist drive to USD 6,500 on a 55 kW crab drive.

Hoist	Duty	Recovered per year	Value per year	Payback on the regen premium
0.5 t chain, 3 m	A3, 60 cycles/h, 800 h	75 kWh	USD 9	Never
1 t chain, 3 m	A3, 60 cycles/h, 800 h	150 kWh	USD 18	50 years
2 t chain, 4 m	A4, 80 cycles/h, 1,200 h	800 kWh	USD 96	11 years
5 t wire rope, 6 m	A5, 20 cycles/h, 2,000 h	1,251 kWh	USD 150	8 years
10 t wire rope, 8 m	A5, 20 cycles/h, 2,000 h	3,335 kWh	USD 400	4 years
20 t double rail, 10 m	A6, 25 cycles/h, 3,000 h	15,635 kWh	USD 1,876	2 years
50 t crab, 12 m	A6 to A7, 20 cycles/h, 4,000 h	50,031 kWh	USD 6,004	1 year

The crossover sits somewhere around 5 to 10 tonnes, and it depends almost entirely on hours, not on capacity. A plant running a 5 tonne hoist on three shifts will pay back a regenerative front end faster than a plant running a 20 tonne hoist for two hours a day.

Published measurements bracket our model without contradicting it. ABB reports a waste handling crane with a 55 kW hoisting motor, a 9 kW long travel and a 4.5 kW trolley saving 15.6 MWh and USD 2,750 a year, which they put at 32 percent energy savings against the resistor technology it replaced. Konecranes quotes up to 30 percent for its regenerative systems. A 2014 study of hoisting motors at Konecranes puts the recoverable share of lowering energy at 20 to 70 percent, which is a wide band and honestly so, because it depends on how much of the cycle is a loaded descent.

Our 50 tonne case recovers 50 MWh a year, more than three times ABB's figure on a similar motor. That is not a disagreement. Their crane handles waste in a shed, ours is a casting bay crab with 20 loaded descents an hour for 4,000 hours. Same physics, four times the duty.

What does reverse power do to the supply upstream?

It pushes the voltage up, and this is not a theoretical concern. A 2007 study of gantry cranes at Kaohsiung Harbour documented unwanted terminal voltage rise caused by regenerative braking of the DC machines, and proposed ways to get rid of it. A 2010 measurement campaign on a gantry crane at Muuga seaport in Estonia recorded the same thing from the power quality side: lowering the hoist and braking the trolley feed active power back into the grid, and because the load varies through every cycle, the energy flow varies with it. Both papers are old and both describe machines that are still in service.

On a plant supply with a stiff transformer, a hoist returning 5 kW for twenty seconds is a rounding error. On a generator set it is not. Cummins addresses the case directly in its application guidance for rubber tyred gantry cranes: reverse power from a regenerative hoist is normally absorbed by other connected loads, but situations occur where it exceeds what those loads are drawing, and the regenerated power is then pushed into the alternator terminals. They keep a separate application note on regenerative loads and reverse power for exactly this reason.

What that means in practice is that a hoist on a genset needs one of three decisions made before delivery. Disable the regeneration path, which turns the drive back into a resistor machine. Size the set and its protection so reverse power is tolerated, which usually means a larger alternator than the load calculation suggests. Or accept that the reverse power relay will trip the set, and find out on site. Most generator protection is set to trip at a small percentage of reverse power, typically in the single digits to low teens, so a hoist that regenerates 20 percent of the set rating will trip it.

Upstream effect	Where it shows up	What to do about it
Voltage rise at the point of common coupling	Lighting flicker, drives tripping on overvoltage elsewhere on the bus	Check the PCC voltage during a loaded descent, not at idle
Reverse power into a generator	Reverse power relay trip, engine speed instability	Decide before delivery, as described above
Interaction with power factor correction	Overvoltage and capacitor stress when the plant bank is live	Ask whether the capacitors are detuned, and at what order
Harmonics at the PCC	IEEE 519 limits on voltage distortion and TDD	A regenerative front end usually improves this, at 0.99 power factor and low current distortion
Metering direction	Savings that never appear on the bill	Bidirectional meter, class 0.5S, before commissioning

The metering line is not a joke. We have seen a plant install regenerative drives, measure nothing, and conclude after six months that the drives did nothing. The existing meter counted import only. Nothing was broken. The savings were simply invisible.

Is a two-speed contactor hoist really non-regenerative?

No, and this is the most misunderstood point in the whole subject. A plain squirrel cage hoist with two speeds and two contactors already returns energy to the plant. When an overhauling load drives the motor above synchronous speed, an induction machine becomes an induction generator. On a 50 Hz four pole motor the synchronous speed is 1,500 rpm, so a descent that pushes the shaft to 1,680 rpm puts the machine into generating mode and current flows back through the contactor.

What it does not do is control anything. The regenerated active power comes with a large reactive draw for magnetisation, so the power factor in that condition is poor, and the descent speed is set by the load rather than by the operator. The brake does the stopping. There is no DC bus to trip, which is why these hoists never show the overvoltage fault that drives everyone to the manuals.

The real differences between the control methods are inrush and wear, not recovery.

Starting method	Typical starting current	Consequence on a hoist
Contactor, direct on line	600 to 700 percent of full load current, with a spike above 10 times at closure	Voltage dip on weak supplies, mechanical shock, brake and coupling wear
Soft starter	200 to 450 percent of full load current	Softer start, but no continuous speed control and no recovery path
VFD	At or below 100 percent of full load current	No inrush, controlled descent, and a place to put the regenerated energy

So the honest sales line is not "regenerative versus non-regenerative". It is "controlled regeneration versus uncontrolled regeneration". A buyer who understands that will ask the right question, which is where the energy goes on the way down, and will not pay a premium for a word.

Does electrical braking replace the mechanical brake?

Never, and the codes say so twice. One hoist industry source puts it plainly: the safety code stipulates that cranes require both an electrical and a mechanical means of braking, with the mechanical side covered by the disc brake and the electrical side by the motor's regeneration capability, which must not allow the lowering speed to exceed the maximum limit by more than 10 percent. That 10 percent is the whole test. Braking that cannot hold speed within it is not a braking means, it is a retarder.

CMAA Specification 70 sizes the hoist brake on motor full load torque at the point where the brake is applied, and distinguishes stopping torque from holding torque. An overhauling load like a hoist needs both. A bridge or trolley needs only enough to stop, and then friction keeps it there. That is why a hoist brake is a different component from a travel brake even when the catalogue shows the same part number.

Fail-safe in this context means spring applied and power released. When the coil loses power the springs close the brake, which is why a power failure holds the load rather than dropping it. OSHA's marine standard states the requirement in one sentence: a failure of the electric power shall stop the motion and set the brakes without any action on the part of the operator. Where a load is carried over people, an output-side emergency brake is added on the gearbox output shaft or the drum flange, sized at the gearbox output torque with a safety factor of 1.5, precisely because a motor-mounted brake cannot protect against a broken input shaft.

Requirement	Source	What it means for a regenerative hoist
Both electrical and mechanical braking required	Hoist industry practice and crane safety codes	The drive does not remove the disc brake, it changes how often it is used
Lowering speed not more than 10 percent above maximum	Same source, quoting the mechanical braking clause	The acceptance test that a regenerative drive has to pass, on load, at full speed
Brake sized on motor full load torque at the brake	CMAA Specification 70	Holding torque and stopping torque are separate numbers, and both are needed
Brake holds 125 percent of rated load, lowering speed within 120 percent	ASME B30.16 hoist requirements	Ask for the test report, not the calculation sheet
Power failure stops motion and sets brakes with no operator action	OSHA 1919.22, marine and longshoring	The reason the brake is spring applied, and the reason the drive must not be able to defeat it

There is one more interaction worth naming, because it is subtle and it is where the Danfoss warning bites. A regenerative drive holds the brake open while it controls the load electrically, which reduces brake wear dramatically and is a genuine benefit. But if the drive is permitted to ride through an overvoltage by speeding up, then the mechanical brake is the only thing left that knows the speed limit. On a conveyor nobody notices. On a hoist, the 10 percent rule exists to stop exactly this design.

Which duty class decides all of these numbers?

ISO 4301-1:2016 classifies crane duty by three things: the total number of working cycles over the design life, the load spectrum, and the average displacement. For hoist mechanisms the standard lets you classify the drive separately from the structure, which matters here because the regenerated energy scales with cycles, hours and hook travel, not with tonnage alone.

Hoisting motors are almost always intermittent duty machines. The Konecranes research on hoisting motors describes the standard case as S3 with a duty cycle of 40 or 60 percent, meaning four or six minutes at rated power in every ten. That is why a 5 tonne hoist can carry a 7.5 kW motor and still lift 5 tonnes: the rating assumes it will not do it continuously.

Class	Cycles per hour	Hours per year	What it does to a 10 t hoist
A3, light	Up to 60	800 to 1,600	Around 1,300 kWh a year. Resistor only, no argument
A4, medium	60 to 120	1,600 to 3,000	Around 2,500 kWh. Marginal, depends on the tariff
A5, heavy	120 to 240	3,000 to 5,000	Around 3,300 kWh. Regeneration is defensible
A6, very heavy	240 to 400	5,000 to 8,000	Over 8,000 kWh. Buy the front end, and buy the meter too
A7 and A8, severe to continuous	Over 400	Over 8,000	Regeneration is the cheap option, and the resistor becomes the maintenance item

This is the number to argue about, not the tonnage. The same 10 tonne hoist recovers four times more energy at A6 than at A4 with no change to the hardware. Which is why a specification that says "10 tonne, regenerative" tells you nothing, and one that says "10 tonne, A6, 300 cycles per hour, 6,000 hours a year, 8 m hook travel" tells you everything.

What goes wrong in the first year?

The following distribution comes from our own service records across hoist installations, not from a published survey. We are labelling it that way because these numbers are ours and a reader should treat them as such.

Symptom	Share	Actual cause
Overvoltage trip on lowering	31 percent	Resistor not connected, chopper disabled in parameters, or resistance set too high
Resistor open circuit or thermal trip	19 percent	Terminals cooked at the resistor end, or a dust-clogged enclosure in a dirty plant
Load drifts or jerks at brake release	17 percent	Brake released before the drive established torque, or the reverse
Chopper transistor failure	11 percent	A resistance below the drive minimum, fitted because it braked harder on the bench
Savings never visible	9 percent	Import-only meter, or no meter at all
Panel overheating	8 percent	Resistor mounted inside the cabinet to keep the cable run short
Unexplained speed increase on descent	5 percent	Overvoltage control left enabled on a hoist drive

The top two items are configuration and installation, not component quality, and both are cheap to prevent. The last one is the only entry that is genuinely dangerous, and it takes thirty seconds to check: look for overvoltage control in the drive parameters and confirm it is off.

Can you check the motor rating yourself?

Yes, with one formula and a calculator, and it is worth doing before you compare two quotes. Required input power is mass times gravity times lifting speed, divided by the efficiency of gearbox, motor and reeving. We use 0.85. Lifting speed is the number that is missing from most quotations, which is why the check so rarely gets done.

Capacity	Lifting speed	Mechanical power at the hook	Input power needed at 0.85	Nameplate we would expect
1 t	8 m/min	1.31 kW	1.54 kW	1.5 kW
2 t	8 m/min	2.62 kW	3.08 kW	3 kW
3 t	8 m/min	3.92 kW	4.62 kW	4.5 kW
5 t	8 m/min	6.54 kW	7.69 kW	7.5 kW
10 t	7 m/min	11.45 kW	13.46 kW	13 kW
5 t, listed at 6 m/min	6 m/min	4.91 kW	5.78 kW	We have seen 4.0 kW quoted

The first five rows reproduce published catalogue ratings almost exactly, which is the point. Once the speed is known, the motor size is not a matter of opinion. The last row is a real table we came across, where a 5 tonne hoist at 6 m/min was listed at 4 kW, and the physics needs 5.8 kW. Either the speed is really about 4 m/min at rated load, or the 4 kW is a short time figure that should have been stated with its duty cycle. Both are answerable in one email. Neither is answerable from the quotation alone, which is why the RFQ question below asks for the duty cycle and the speed in separate fields.

What should the RFQ say?

Ten lines. Any hoist supplier can answer them, and the answers separate the ones who build hoists from the ones who assemble them.

One. Rated capacity, lifting speed at rated load, and hook travel. Without the speed, the motor rating cannot be checked, because power is mass times gravity times speed.

Two. Motor output, duty class and the S3 duty cycle percentage, stated separately from any short time overload figure.

Three. Control method: contactor two-speed, soft starter, or VFD with the drive family and frame size named.

Four. For a VFD, whether the braking chopper is built in, and the minimum permissible resistance from the drive manual.

Five. Resistor rating in ohms and watts, mounting location, enclosure rating, and the thermal protection arrangement.

Six. Whether a regenerative front end is offered, its premium, and whether the drive can be upgraded later without replacing the panel.

Seven. Brake type, spring applied or otherwise, torque at the brake shaft, and whether an output-side emergency brake is available.

Eight. Test evidence: 125 percent static hold, lowering speed within 120 percent, and the lowering speed limit with the drive in electrical braking only.

Nine. Expected annual cycles, hours, average hook travel and the tariff you pay, so the supplier can show the energy calculation rather than a percentage.

Ten. Whether the regenerated energy will be measured, and by what. A bidirectional meter is the only way to find out whether any of this worked.

We build hoists from 0.125 to 100 tonnes and we have quoted both answers, resistor and front end, for the same machine more than once. The number that decides it is not the tonnage. It is hours times cycles times hook travel, and if a supplier quotes recovery in percent without those three inputs, the percent came from a brochure.

If you are sizing a hoist for a duty you have not fully defined yet, talk to us before the drive is ordered. Feed us the cycle and we will give you both numbers. Our hoist and accessory range covers chain and wire rope units from 0.125 to 100 tonnes, and the electrical package is quoted separately so you can see what the resistor costs and what the front end costs.

Frequently Asked Questions

Can I add a braking resistor to an existing hoist drive?

Only if the drive has a built-in brake chopper and terminals for it, which most hoist-rated drives do and many general purpose drives do not. Check the manual for two things: whether a braking transistor is fitted, and the minimum permissible resistance. If the drive has no chopper, you add a separate braking unit rather than a bare resistor, and that unit needs its own supply and its own fault output wired back to the crane controls. Retrofitting without changing the drive parameters is the most common way to spend money and still trip on the first descent.

Why does the hoist trip only when lowering and never when lifting?

Because lifting draws power and lowering returns it. The trip is the drive protecting its DC bus from energy it cannot dispose of, so the fault is in the energy path: a disconnected resistor, a chopper that is disabled in the parameter set, a resistance too high to pass enough current, or a thermal interlock that has opened. A drive that trips at idle or at power up is a different problem entirely and points at the supply. Record the direction, speed, load and brake state at the moment of the trip before anyone resets the fault.

Will a regenerative hoist work on a diesel generator?

It can, but the generator has to be part of the decision. Reverse power from a descending load is normally absorbed by other loads on the same supply, and when it is not, it is pushed into the alternator terminals. Generator protection is usually set to trip at a small percentage of reverse power, so a hoist that returns 20 percent of the set rating will shut the set down. The three options are to disable regeneration, to size the set and its protection for reverse power, or to accept the trip. Decide before delivery, not during commissioning.

How do I know the recovered energy is actually being credited?

Install a bidirectional meter with class 0.5S accuracy on the hoist feeder before commissioning, and read it after a normal week. Import-only meters cannot show export, so a plant can run regenerative drives for a year and see no change on the bill. The meter also settles arguments about whether the duty you described to the supplier matches the duty the crane actually runs, which is usually where the discrepancy lives. Ask us for the metering point on any quote you take from us as well: contact the engineering team and we will mark it on the single line diagram.

Is regeneration worth it on a one tonne chain hoist?

No, and the arithmetic is not close. A one tonne chain hoist lowering 3 m at a typical light duty returns about 150 kWh a year, which is USD 18 at USD 0.12 per kWh. A regenerative front end costs several hundred dollars more than a resistor, so the payback runs to decades, longer than the hoist will last. Buy the resistor, keep it outside the panel, and spend the difference on a brake that releases cleanly.

What is the difference between a braking resistor and a regenerative unit?

The resistor turns the energy into heat and the regenerative unit turns it back into supply current. The resistor is cheaper, simpler, has no grid interaction and works on any supply including a generator. The regenerative unit saves the energy, removes the heat from the building, improves power factor and harmonics, and introduces a set of questions about reverse power, metering and protection that the resistor never asks. On machines below about 5 tonnes the resistor wins on money. Above 20 tonnes with real duty, the regenerative unit usually wins on money as well as everything else.