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What is a variable speed drive?

You might know your variable speed drive by a different name, such as inverter, AC drive, motor speed controller etc. but they all do the same job - control the speed of an electric motor. In order to do this, they are made up of a series of PCBs that control the drives power stage which receives and feeds the current to the motor to control speed and/or torque. Generally, the larger the power required, the larger the drive. We see drives small enough to fit in your hand to those taller than the average adult male.

Variable speed drives can operate without issue for a long time. They often only begin to fail due to environmental issues that cause components within the drives to degrade more rapidly. It’s not uncommon for companies to get over 10 years out their variable speed drives, which can cause people to forget about how important they are to their processes as they do their job quietly for a long time before failure. 

With our tips below, you can ensure you keep your drives in optimum condition, reducing the chances of unplanned downtime causing disruption to your operation.

How to prevent VSD failure

Keep the environment clean

Dust and dirt in a production environment can easily clog up the heatsinks on drives. This can cause the inverter to overheat, which is one of the biggest causes of failure. Running an ESD vacuum cleaner over the heatsink or blowing it out with compressed air is a good way to clean out the dust and dirt. If using a compressor ensure the surrounding air is clean and free of moisture, so as not to cause more harm than good.

Use the correct protection

Ensuring you get the correct ingress protection rating for your environment will go a long way to prolonging the lifespan of your variable speed drive. Drives rated IP00 or IP20 are particularly exposed to contamination from dust which will restrict your airflow. Higher IP ratings are also required for moist environments, otherwise moisture will lead to problems such as corrosion to circuit boards.

Maintain it regularly

Prevention is always better than cure and completing maintenance on your drives every so often will prevent them from failing unexpectedly. Aside from regular maintenance such as vacuuming or blowing out dust and dirt, checking control connections and ensuring air flows freely, we recommend servicing your drives every five to eight years to replace components that degrade with age. This enables you to get the maximum lifespan out of your drives and reduce unexpected downtime.

Keep the drive ventilated

Variable speed drives require sufficient air flow through them to keep cool and free from overheating. When installing the drive in the control panel, you need to ensure that it is well ventilated. Another thing to check to ensure air flows freely is the fans on the drive. These fans play an integral part in cooling the components within the drive, such as the electrolytic capacitors, so it’s important to make sure there are no obstructions stopping the fans from doing their job. Without sufficient cooling electrolytics capacitors dry out much faster causing intermittent faults like tripping out. If your installation environment is higher than 40°C many manufacturers recommend derating the output by up to 15%.

Tight is right

Periodically checking connections is something that is missed out of many preventative maintenance plans but it is important as loose connections can be attributed to many problems including extra heating and/or arcing. We’ve seen drives where the connectors have actually been melted down. Other issues that can occur from loose connections include intermittent operation and reduced efficiency. We recommend checking your control connections annually.

To summarise our five tips

  1. Clear dust and dirt with an ESD vacuum or compressed air if the air in your environment is clean and dry

  2. Keep the drive ventilated by ensuring fans are clear from obstruction and rotating freely

  3. Ensure your drive has the correct IP rating for your environment to ensure adequate protection

  4. Check the control connections annually to reduce faults caused by loose connections

  5. Prevention is better than cure - service drives every five to eight years to replace aging components before they fail