Heat when an electric winch lowers a load

Raising a load takes energy, and it is easy to assume lowering simply gives it back for free, but on an electric winch lowering is a real engineering problem. As the load descends, it gives up the potential energy it gained being raised, and that energy has to go somewhere. If it is not managed, it tries to drive the winch faster, and controlling the descent means absorbing that energy, usually as heat. So lowering a load, especially a heavy one or one lowered often, generates heat that the winch must handle, which ties into the wider thermal story our note on motor cooling and heat covers and the control our note on variable speed describes.

Why lowering gives up energy

A raised load holds potential energy, given to it by the work of lifting it. When it is lowered, it releases that energy, and on a winch the released energy tries to turn the drum and the motor, driving the winch rather than being driven by it. To lower under control rather than letting the load run away, that energy must be resisted and absorbed, not simply allowed to accelerate the descent. So controlled lowering is fundamentally about absorbing the energy the load gives up, and where that energy goes, into heat or back to the supply, is what distinguishes the methods of lowering an electric winch uses.

Lowering on the mechanical brake

The simplest way to control a descent is with the mechanical brake, letting it absorb the energy as the load lowers. The brake resists the load, slowing the descent, and the energy becomes heat in the brake. This is simple and works, but it loads the brake with the lowering energy, which on heavy or frequent lowering generates real heat the brake must shed, and wears the brake. So lowering on the brake alone suits lighter or occasional lowering, while heavier, more frequent lowering benefits from a method that absorbs the energy elsewhere, sparing the brake from carrying the descent energy every time.

Dynamic braking

A common way to absorb lowering energy electrically is dynamic braking. As the load drives the motor, the motor acts as a generator, turning the lowering energy into electricity, and that electricity is burned off as heat in a resistor. So the load is resisted electrically, controlling the descent, and the energy goes into the braking resistor rather than the mechanical brake. This spares the brake and gives smooth electrical control of the descent. The resistor must be sized to absorb the energy and to shed the heat, especially on heavy or frequent lowering, but dynamic braking is an effective, common way to control lowering on an electric winch without overloading the brake.

Regenerative drives

A more efficient way to handle lowering energy is a regenerative drive, which feeds the energy back to the electrical supply rather than burning it as heat. As the load drives the motor as a generator, a regenerative drive returns that electricity to the supply, recovering some of the energy instead of wasting it. This avoids the heat of a braking resistor and is efficient, but it needs a capable drive and a supply that can accept the returned energy. So a regenerative drive suits heavy, frequent lowering where the energy is worth recovering and the system can take it, while simpler duties use dynamic or mechanical braking. It is the same variable speed technology that also gives smooth control, the subject of our note on variable speed and soft start.

Lowering and the duty cycle

Because lowering generates heat, it is part of the winch's thermal duty, not separate from it. A winch that lowers heavy loads often adds the lowering heat to the heat of its motor and any braking, and all of it has to be shed within the duty cycle, the subject of our note on duty cycle. So a winch sized only for the lifting duty may overheat if it also lowers heavy loads frequently, because the lowering heat was not accounted for. Considering the lowering as well as the lifting when sizing the winch and its braking is part of giving it the thermal headroom for the whole job, not just the lifting half of it.

Smooth, controlled descent

Handling the lowering energy well also gives a smoother, safer descent. A controlled lowering, whether by dynamic braking or a regenerative drive with variable speed, brings the load down steadily at a set rate rather than letting it surge or run, and eases it to a stop without shock. This smooth descent is kinder to the rope and the load and safer for whatever is below, avoiding the shock loads a jerky or runaway descent would cause, the subject of our note on shock loading. So managing the lowering energy is not only about heat but about control, giving a descent that is steady, gentle and safe.

Choosing how to lower

The right way to handle lowering follows the duty. Light or occasional lowering can be handled on the mechanical brake; heavier or more frequent lowering benefits from dynamic braking to spare the brake; and heavy, frequent lowering where efficiency matters suits a regenerative drive that recovers the energy. The braking and the drive are sized for the lowering energy as well as the lifting, so the winch lowers smoothly and does not overheat. We consider the lowering, not just the lifting, when specifying an electric winch, so it handles the whole job, raising and lowering, smoothly and within its thermal limits rather than struggling on the descent.

A winch that lowers as well as it lifts with us

We specify the braking and drive for the lowering energy as well as the lift, so the winch lowers smoothly and stays cool. See the range in our winch catalogue, and read how the motor cooling, the duty cycle and variable speed bear on lowering. Tell us how much and how often the winch lowers, and we will specify the braking that handles the lowering heat and gives a smooth, controlled descent.

Frequently asked questions

Why does lowering a load generate heat?

Because a raised load holds potential energy, and as it lowers it gives that energy up, trying to drive the winch. To lower under control rather than letting the load run away, that energy must be absorbed, usually turning into heat, in the brake or a braking resistor, unless a regenerative drive feeds it back to the supply.

What is dynamic braking on a winch?

A way of controlling a descent electrically: as the load drives the motor, the motor acts as a generator, and the electricity it makes is burned off as heat in a resistor. This resists the load and controls the descent while sparing the mechanical brake from carrying the lowering energy every time.

What does a regenerative drive do?

It feeds the lowering energy back to the electrical supply rather than burning it as heat. As the load drives the motor as a generator, the drive returns the electricity to the supply, recovering some energy and avoiding the heat of a braking resistor. It needs a capable drive and a supply that can accept the returned energy.

Does lowering affect how I size a winch?

Yes. Lowering generates heat that adds to the motor and braking heat, all of which must be shed within the duty cycle. A winch sized only for lifting may overheat if it also lowers heavy loads frequently, so the lowering is considered alongside the lifting when sizing the winch and its braking.