Selecting the Right AC Drive

Installing the drive

There are so many options when it comes to selecting an AC drive that it can be difficult to know which is best for you. Not only is there hundreds of brands to choose from but there are also a multitude of types as well as communication and control options available to confuse the user. Here we have set out a handy selection guide to steer you in the right direction when it comes to selecting a brand new AC drive.

First Things First – Know Your Motor

The first step in choosing the right inverter drive is to check the nameplate of your motor. This is where all the important information such as supply voltage, kW size or horsepower, and amp rating is found. Nameplates often have a lot of information on them so if you aren’t sure what is important and what isn’t, take a photo of the nameplate and email it to us.

All this information is important for specifying the correct AC drive, so make sure to take a note. If you need to convert the horsepower to kW simply multiply the horsepower by 0.75 to get the correct kW size. Please note that a DC drive will be needed for a DC motor.

What Are Your Requirements?

Understanding the requirements of your application is key to making sure you don’t pay over the odds for your variable speed drive. Nowadays, modern drives tend to have both normal duty and heavy duty ratings which can also be referred to as variable torque (ND) or constant torque (HD). In basic terms, constant torque can be compared to driving on a motorway where speed is steady for a number of hours whilst variable torque is more like city driving where you are constantly stopping and starting. Applications including fans and pumps are frequently normal duty as they ramp up speed gradually and then run for hours, whereas other applications like conveyors and compressors are heavy duty as they start and stop with the loads changing frequently every hour.

Where Are You Installing the Drive?

Considering where your inverter drive will be installed is the next step in selecting the right AC drive. Many drives feature an IP rating which stands for Ingress Protection. The IP rating is usually a two digit number with higher numbers offering higher protection. Users in wet or corrosive environments may want to mount the variable speed drive in a panel or choose a higher IP rating. We suggest that inverter drives that are subject to wash down procedures or extreme conditions are sealed to at least IP65 or IP67.

Controlling Your AC Drive

Take some time to think about how you want to control the speed of your variable speed drive. You have a few options when it comes to controlling the drive including keypads, a pot or a PLC. If you are mounting your AC drive in a panel or somewhere else where it is not easily accessed, a remote keypad or PLC could be considered.

Determine Your I/O Requirements

Your new AC drive will need to interact with other devices in your plant, so you need to know how many inputs and outputs you require and the type of inputs and outputs.

Digital inputs are used to allow the inverter drive interact with other devices such as PLCs, switches and push buttons. These signals can be used for functions such as start/stop, forward/reverse, external fault and preset speed selection.

Analogue inputs enable the drive to be controlled by a simple 0-10VDC or 4-20 mA signal. This can be something as simple as a pot or feedback from a PID controller.

PTK inputs can be used to monitor a simple temperature sensor within the motor windings to avoid damage in the case of an overload.

Digital and relay outputs are useful when you want to notify external devices of your drive’s status, for example if there is a fault or when it has reached its set speed.

Communication Requirements

There is an overwhelming amount of communication options available such as Profibus, CanBus, Ethernet and Modbus. Thankfully, nowadays most drives such as the Unidrive SP by Control Techniques and the A1000 by Yaskawa have expansion modules that you can plug into the unit which provide access to most communications protocols.

Programming the Variable Speed Drive

Programming your AC inverter drive can appear daunting. Despite it being estimated that 60% of operators only ever use the first seven parameters, too many manufacturers focus on high-end applications. This makes programming more simple applications a lot more difficult than necessary. We recommend the Commander SK range for simple applications as it is so easy to set up, with 10 preloaded parameters for standard tasks. If your application is more complex, we recommend the Yaskawa A1000 which offers more functionality than the Control Techniques inverter drive but is also easy to set up.

To Filter or Not to Filter?

Without a filter inverter drives send electrical noise back into the mains supply. Some variable speed drives come with an integrated industrial filter, such as the Control Techniques Commander SK and Unidrive SP, whereas others like the Yaskawa A1000 and V1000 offer no internal filter at all. If you are using multiple drives in one panel a drive without an internal filter may offer you a cost saving as one filter can be used to supply all of the drives. Residential or commercial drive installations, such as an escalator in a shopping centre, will require a commercial filter.

Brand Selection

As we have already mentioned – there are so many manufacturers of AC drives. At Northern Industrial, we prefer Control Techniques and Yaskawa but Lenze, Allen Bradley, Mitsubishi and Siemens all offer good value inverter drives. These manufacturers all use their own parameter structure or software for configuration but Control Techniques offer a good balance of simplicity and functionality. We set up these drives everyday for customers and can offer the best technical support for these brands.

If in Doubt

Still not sure about which is the best inverter drive for your application and setting? Drop us an email or give us a call and we can help you specify the right variable speed drive at the right price for your applications.

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