Low Voltage or Direct Control?
The terms "low voltage control" and "direct control" refer to the systems that control electric chain hoists. Columbus McKinnon is one of the few electric chain hoist manufacturers to offer both control systems. In the case of direct control motors, the direction signal is transmitted along the four-pole 415V AC 3P+E power cable.
Direct motor control units manage the order of phases L1, L2 and L3 and supply power to the hoist rotor so that it turns in one direction or the other by reversing the phases. There are no direction contactors inside a direct control Lodestar hoist; they are inside the controller.
With low voltage motors on the other hand, the direction signal is transmitted along an additional cable (16A 110V 4 pole yellow connectors) which acts on contactors inside the motor itself.
There are pros and cons to both control systems; although many factors, such as working safety, margins of manoeuvre and - not least - economic considerations should be considered when deciding which system is best for you. Another thing to consider is that the majority of rental equipment in the U.K. is low voltage and in Europe the preference tends to be towards direct control. Some users prefer low voltage simply because you can control a single unit with a mains supply and a single channel hand pendant commonly known as a pickle.
One important difference between the two models is the presence of an end-stop unit inside the motor, i.e. electrical limit switches.
Direct control motors use mechanical chain stop systems; a two part mechanical block with a nylon ring is fitted at one end of the load chain which stops the chain from travelling straight through the motor (Picture right) when this mechanical stop comes into contact with the body of the hoist, the overload protection device (clutch) activates.
The low voltage control hoist has a chain length control system which stops the motor when the chain is about to reach the end, the limit switches (Picture photo below) are calibrated so as to stop the motor automatically a few links before the chain ends, thus preventing it from travelling straight through the hoist.
In the specific case of the Lodestar hoist, the number of safety links is factory-set on the thin notched plates in the end-stop unit, this can be adjusted by competent trained technicians if required. Correct limit switch operation depends on the exact sequence of phases L1, L2 and L3 in the hoist electrical power supply.
An incorrect phase sequence can impair the function of the limit switch system; most good quality controllers have phase sequence indicators or phase reverse protection built in to overcome this problem.
The direct control hoist does not pose this problem; in short, the substantial differences between the two hoists are the presence or absence of contactors on board and the use of two different end-stop safety systems.
The hoist is the same in both cases; the way it is controlled quite different.