VFD Elevation Limitation?

[T. J.]

When researching specifications for VFDs, I keep seeing it called out that the unit is to be installed at or below 1,000 m (3,280 ft) above sea level. I struggle to see how that is pertinent to an electronic device, but I'm definitely no expert. Since my shop elevation is about 4,000 ft (1,219 m), I would be out of spec.

My instinct is to ignore this requirement, but I figured I'd ask the brain trust. Is this really important? If so, why?

 

[rwm]

I'm sure it has something to do with the pressure/volume of the magic smoke.
Robert

 

[jwmelvin]

Lower-density air has less heat-transfer ability. I’d just pay attention to the cooling air flow (don’t install in a closed box). And maybe go up a size on the VFD selection.

 

[mksj]

Some electrical components have deratings for altitude, I do not know the specifics, but may be that the cooling ability may be less. VFD deratings usually are for components run at maximum load for sustained intervals. I would not worry about it.

 

[MrWhoopee]

Maybe the capacitors will explode at the lower air pressure. (JK)

"As altitude is increased, the air is less dense – cooling capacity of the air is decreased as altitude increases making heat removal via air less effective"

https://www.psma.com/sites/default/files/uploads/tech-forums-safety-compliance/presentations/is63-design-considerations-power-supplies-high-altitude-applications.pdf

If you're concerned, add an extra cooling fan and carry on.

 

[rabler]

Yes, cooling issue. Most decent VFD's monitor their own temperature, so they will cut out or derate themselves in various ways if they start to get too hot. Check also the VFD's max operating air temperature. If you are operating a higher altitude but not in an environment where the VFD temperature is near it's upper limit, you essentially have already compensated.

 

[mksj]

The below (altitude/temperature) derating may be helpful, the derating is based on 100% duty cycle at rated output, as rabler mentioned VFD's do have over temperature sensors which should shut down the VFD if exceeded. Long term heat will effect the longevity of components, the electrolytic capacitors are probably the most significantly effected. One could push the VFD sizing up if one was at higher elevations or temprature enviroments. Since the duty cycle and maximum current output is short in most hobbyist application, I would not have any concerns about magic smoke.

 

[rabler]

Per @mksj's datasheet: "... decrease 1% of the rated current, or lower 0.5*C of temperature for every 100m increase in altitude."

You're just a tad over 200m above the 1000m point, so as long as you reduce the operating temperature by about 1*C (to 39*C, or to about 102*F) you're good to go. That would be the air temperature that the VFD is pulling in at it's cooling input fan, or the temperature of the air in the cabinet of the VFD. Of course your particular VFD may be rated slightly differently, but these are probably all driven by UL and other industry testing standards.

In all reality it's not going to make that big of a difference even if you didn't reduce the temperature. Probably some statistical issue like it'll reduce the Mean Time Between Failure (MTBF) by a few percentage points.

To some extent, at higher altitudes also cause air to have less electrical insulation effect (Paschen's Law), so more chance of arcing inside the VFD. That may be why the VFD has a hard limit of 2000M in the above example.

 

[T. J.]

Ok, the cooling issue makes sense. The bottom line is, it’s not going to make much difference in my application (lathe motor). I won’t be operating anywhere near the max duty cycle or temp. (If it’s anywhere near 102 F in my shop, I’ll be working on the AC not running the lathe .

Thanks guys!