It’s a harsh world… part 3 – Drives vs Low temperatures

Wednesday, March 2, 2016
Icebreaker Polar Star in the artic between ice floes

3°C / 37°F – that’s the temperature my phone is showing me as I sit down to write this. That’s not quite cold enough for the snow to start flying, but it sure is cold enough for me to throw on my jacket, hat and gloves when I head outside. I’m in Hamburg, Germany – in other countries, and in higher altitudes, the temperatures drop even further. Sure, we’re heading into spring. But, for most of us, it just isn’t getting warm enough fast enough. However, we’re not here to talk about how the weather is affecting me; you’re all here to find out what low temperatures mean for your AC drives. Should they also find a way to button up for those cold, dark days? The short answer is – absolutely.

The slightly longer answer is, of course, a bit more complex than that. As you saw last time, there are quite a few different types of enclosure ratings for your AC drives. But, only UL Type 3R and 4X specifically deal with some of the particular challenges of cold weather environments. While these UL Type ratings deal with rain, snow, sleet and ice formation, they don’t specify any particulars about the temperature surrounding the AC drives.

If you look through the specifications table in any AC-drive installation manual or design guide, you’ll find that the drive has a minimum and maximum operating temperature range. Quite typically, this range bottoms out at an all too common, for much of the world, -10°C/+14°F. When running at this low temperature, the AC drive doesn’t always have the ability to provide full capacity, either, so derating is required when sizing and selecting the right product for your application. You would also find a separate rating for minimum storage temperatures as well. For some products, this is -25°C/-13°F and for others it’s -40°C/-40°F. It’s important to know where to find this information if your drive will be operating in these types of cold temperatures.

What exactly happens with the AC drive when it experiences these low temperature conditions? Well, many AC drives use a liquid crystal display, or LCD, for the control panel display. When temperatures drop, the LCD becomes slow to refresh its contents. The colder it gets, and the longer the LCD screen is exposed to these conditions, it ceases to be functional to program with. As you can probably imagine, when a liquid crystal display turns into a frozen crystal display, it is no longer useful. Additionally, electrolytic capacitors lose some capacity, resulting in a loss in starting torque in constant torque applications, and an increase in DC ripple voltage which can damage the AC drive. Fortunately, products in the VACON® 100 series contain thin film capacitors that aren’t susceptible to low temperatures in the same way as the electrolytic capacitors, which results in a lower storage temperature and no need to derate below freezing. Lastly, in extremely low temperatures, potted components can crack, dramatically reducing the lifespan of the product.

Obviously, avoiding or combatting these low temperatures is extremely important to keep your AC drive functioning in the best, most reliable way. When these temperatures are encountered, providing the appropriate amount of external heating varies widely based on both installation methods, relating to enclosure class and location, as well as the operating profile of the AC drives. In some applications, the AC drive is almost always running, which means it’s generating heat and doesn’t really need help from an external heating source. If it’s in an enclosure with other devices and the AC drive is large enough, perhaps an external heater is only required if the drive were not running. In other applications, the AC drive might be mounted outside where it’s nearly impossible to control the conditions. In this case, you may find options such as the VACON® 100 X, which has a temperature-controlled heating option that can be integrated into the drive enclosure itself. This option is separately powered by a 230V single-phase supply, which allows it to keep the AC drive warm even if the power supplied to the AC drive directly is removed.

In other applications, AC-drive operation is largely process-dependent based on the application demand and also redundancy. For constant torque applications, such as cranes and hoists where motors are run less often, both the AC drive and the motor should be warmed to maintain peak operating capability. Quite many products within the Danfoss Drives portfolio have DC injection or motor pre-heat functions that can be actively temperature controlled or activated just before startup for instance. AC drives operating pumps and fans also aren’t always running, and are rarely operating at full speed. AC drives in these conditions would require a larger amount of heating applied far more often. If any of these applications are critical, these heating systems should almost always be running at low temperatures to ensure that the AC drive is protected and ready to go when called upon.

As you can see, combating these cold temperatures isn’t necessarily difficult. But, depending on the application, installation location and surrounding environment, it’s important to know that the easy solution – adding an external heater – isn’t always enough to protect your AC drives. It’s very good to know that heaters inside an enclosure will help with both the cold and at least some of the humidity, but may not account for all of the moisture in the air in extreme cases.

Dealing with water vapor, specifically, is tricky because even if your AC drive is IP66/UL Type 4 rated, the moisture always seems to find a way in. In these types of enclosures, differences in air temperature result in differences in air pressure. In physics, especially in Thermodynamics, we learn that a system prefers to be in equilibrium and air pressure is no different. As the pressures inside and outside equalize, vapors are pulled in resulting in an opportunity for condensation and potentially frost where it’s not supposed to be. Using a dehumidifying system will definitely help. But, if you want to have your AC drive somewhere where controlling humidity is near impossible, Danfoss Drives may have a solution for you. Thanks to the GORE® Vent featured in the VACON® 100 X, VACON® 20 X and VLT® Decentral Drive FCD 302 products, humidity and moisture is no longer a concern. This GORE® Vent is made with a material that allows the drive to ‘breathe’, resulting in air pressure equalization through a moisture-proof barrier.

As you can see, even a topic as seemingly clear-cut as low temperatures even has its unique challenges. Making smart, informed decisions will help ensure that your investment operates worry-free for several years. We here at Danfoss Drives have worked on installations in some of the coldest environments in the world. So you can count on us to help make sure you have the most optimal solution for your application.

Authors: Jake Roeder, Global Product Marketing Manager, Danfoss Drives and Abraham González Ponce, Application Knowledge Manager, Application & Service Products, Danfoss Drives

Photo of icebreaker Polar Star by Ville Miettinen (wili_hybrid)