Spoilt for choice

Primarily, whether it is a motor, gearbox or inverter, the importance is that it achieves fit, form and function requirements. Followed by how easy is it to replace if for an existing application or how easy to tie in to your designs.

Decisions might focus on individual components or “overall” system evaluation. For example, is it reliable, “ease of change”, running costs, or initial purchase costs that are key factors. The answer to these points will help to guide you in a certain direction.

Let’s take these considerations through a few examples for a conveyor drive system.

This may be using a standard asynchronous induction motor (IE3 or IE4 efficiency), with a worm gearbox and a basic general purpose IP20 inverter or maybe even just connected DOL as fixed speed. Will it do the job? Yes; Will it fit? Yes; Will it be cheap? Yes; Will it future-proof? Maybe not...

Where energy is the focus the company might use an IE4, IE5 or IE6 motor, possibly with a very highly efficient gearbox and  a PLC controller and more advanced inverter. It will do the job but will almost certainly cost more. Is it worth the cost? In this system, the motor and gearbox are more efficient, whilst the variable frequency drive brings enhanced control and performance and can dramatically reduce running costs, potentially achieving payback in less than two years.

Another similar application with similar components could be a more integrated solution. It could employ a motor with a built in drive and possibly a gearbox. This gives many of the same efficiency benefits but is much simpler to install, reducing installation costs.

The final application could be a conveyor system in a food, beverage or pharmaceutical plant. Here there are other considerations such as hygiene, approvals, audits and reliability. Previously, there have not been many options available and plants had to accept that the drive systems wouldn’t be fully hygienic, efficient or easily controllable without high IP rated panels.

Another historic factor was an acceptance that if hygiene washdowns took place, then the drive system either had to be “bagged” or risk premature failure. This has changed and stainless steel IP69k motors can be supplied with efficiencies up to IE4, which could be used with efficient helical bevel stainless steel gearboxes and controlled by an IP66 inverter. This satisfies both the fit form and function criteria but also all reliability, audit approvals and washdown tolerance needs. This will require slightly higher initial investment but will result in reduced lifecycle costs, potentially achieving payback in a matter of weeks which has been proven on numerous occasions.

Selecting a VFD/inverter can leave some system designers uncertain about their options. Does it need to be IP20, IP55 or IP66, is a general purpose drive ok or does it need to be application specific and is basic control ok or is PLC functionality required?

These are only a snapshot of the basic questions if someone asks for a drive, other options could be switched or unswitched, filters or not, and more. Like motors, there is similar fit form and function requirement. Is it to be mounted in a control panel or on the wall near the application and what are the environmental conditions?  Beyond that, the functionality is more about the application itself and what level and ease of control is required.

Brian Bannister is motor specialist at Lafert Electric Motors

www.lafert.com