VFD reliability

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ptonsparky

ptonsparky

Tom
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
I would like to start using VFDs for Ag related projects. Some of the low cost drives are competitve with starters plus have all the bells and whistles that I add as extras. My biggest worry is operating them for extended periods in climate extremes, mostly heat, and dirt. The enclosures will often times be exposed to direct sunlight with 90 to 105 degree daytime temeratures. Ventilation would be required but along with that comes the dirt. Most of these installations will see little or no maintenance. Have any of you tried these in similar applications and were you satisfied with the results?
 
Many VFD manufacturers will not provide their VFD in a NEMA 4 enclosure, because of temperature concerns. I realize you may use NEMA 3R, but considering many manufacturers hesitation to put the VFD in a NEMA 4 box, they may be concerned with extreme temperatures.
 
I have gone NEMA 4 with an air-air heat exchange or air conditioner for the enclosure. I think with your ambient temperature and direct sunlight you are going to find the heat load will most likely require the airconditioner. However, you may find that adding either of those no longer makes it an attractive price point. Go over 105F operating temperature and the VFD's have to be derated.

Tony
 
I would most definitely try one on a single motor before I invested in a whole series.
If I could find one that matches the application and operating conditions, I might experiment.
If you're wondering if it will be as dependable as your present motor control system, I doubt it, but others may disagree. What are you using now?
If this application is for something like ventilating a chicken (poultry) house, I doubt if you will have much success. Between the heat, dust and waste gases (ammonia for one), it's a severe environment and especially hard on force ventilation equipment. The expense and hassle required to protect the drive from the environment would be pretty big.
Plus...if you're a poultry producer, you know how important ventilation is on a hot summer day....lose your ventilation and you can lose your chickens in a hurry.
It's been a long while since I specified any VS drives, and I'm sure that the technology, dependability and performance has improved.
Others will have more recent experience.
Hope this helps
steve
 
we put VFDs in NEMA gasketed enclosures pretty regularly.

it is a real problem in warm areas. heat exchangers and A/Cs add substantial cost.

the lowest up front cost is to use a vortex cooler with a thermostat.

one thing that you may find is that there is no where near as much heat generated by the VFD as you might think. often they are run for only short periods of time at far less then maximum load.
 
I've put them in 3R enclosures in machine shops, where the air quality can just be horrendous, in that case with oils and cutting fluid vapors. The back frame of almost all VFDs is an aluminum heat sink, and bolting them onto an enclosure has never generated any significant heat doing that.

But then, those are not large continuous loads such as a fan might be, and indoors out of direct sunlight. You can always cut a heat exchanger into a box if need be. The drive will have a thermal cutout with a display of the event, and I see more positives with VFDs than manual starters.
 
Keep in mind what you are referring to cost wise, are most likely 6 pulse drives, which are notorious for producing harmonics back onto your system and having a negative effect on your motors, unless proper filters are provided. This will drive the cost up.

You need to check all the aspects of what woule be required to mkae sure you are doing your economic analysis using apples to apples. What may seem attractive out of the box, may cost more after it is up and running.
 
I have put several Yaskawa VFD's for air handler fan applications on roofs here in SW Florida. The enclosure is in direct sunlight and over 100 deg F. If possible a NEMA 3R ventilation kit helps tremendously with air flow and keeps the VFD from tripping on overheat. I recall the max temp for a Yaskawa is 120 degrees. Mounting the heatsink out of the back of the enclosure helps as does putting a sun shade over the enclosure.
 
Some manufacturers have a drive that needs no enclosure, the unit itself is rated 4x, and it has conduit hubs built in. I think I saw an ad for Baldor, but I've seen others as well. Could you mount this out in the open so that the heatsink is in free air?
 
petersonra said:
the lowest up front cost is to use a vortex cooler with a thermostat.
Click to expand...

I saw vortex coolers on a couple cabinets in a smoke house, and it seems they wanted like 40CFM- true enough about the lo upfront cost, but I was glad I didn't have pay for the air supply. Gotta make sure it is clean, dry air if used.

I installed a fountain controller underground in a chlorine vapor environment- I did what boater Bill said, cut the heat sink thru the enclosure wall. Then I resealed it. This was a repair for a prior electricians fix- he added the raintight vent kits to an otherwise perfectly good sealed NEMA 4 enclosure, and ruined some of the internals.
 
I know that some of the TB Wood's Ultraconn drives are mounted on a very solid, heavy foundry casting type case, and they close up like a freaking vault door. I have found these to be very good in dusty, dirty, and oily envirionments. They put me in mind of an old Crouse Hinds type hazardous location enclosure (although they aren't) with a drive inside.
 
Very few drive packages are designed for direct sun exposure. I know of no VFD that is designed to operate in an environment exceeding 40deg. C, which is 104F. Your ambient is already close to that, adding direct sun will raise it by 30+ degrees! Your VFDs will not last without an air conditioner. A heat exchanger will NOT work for you, you must have at least a 10 degree delta between max. ambient and max. internal temp. for a heat exchanger to function at all, 20 degrees is best.

What most people do on aggy pump panel VFD applications is to build a small sun shed around the VFD. It can be a simple cheap little lean-to type of arrangement, just something to keep the heat gain from getting out of control. Then you can use a sealed NEMA 4 or NEMA 3R enclosure. Don't ventilate, you will get condensation on the critical components and they will short.

The other thing to watch out for is if the environment even gets below freezing. If so, you MUST supply an input isolation contactor that is controlled by a thermostat on the heat sinks so that power is kept off of the VFD input terminals until the heat sink is above 40deg. F. if not, the capacitors will explode! I have warned people of this time and time again, they never believe me until it happens. When it does, the cost to repair is often more than the replacement cost because the capacitor goo gets all over everything.
 
On venting the enclosure, at least add some Crouse-Hinds drains or vents if your are not going to install a NEMA 3R filter kit. I had a situation with several tower fan VFD's outside in NEMA 4 boxes with no sun shades. During the day the enclosure was getting hot and expanding slightly, interior temps going up. Afternoon rain comes along. Quickly the enclosure cools, as it cools, it would draw in moisture, wicking is the term. Sun comes back out, now the enclosure gets hot again with moisture in it. The enclosure would pass the hose spray test, and took us a while to figure out how moisture was entering.

The moral of the story, Vent kits and sun shades.
 
RayS said:
I saw vortex coolers on a couple cabinets in a smoke house, and it seems they wanted like 40CFM- true enough about the lo upfront cost, but I was glad I didn't have pay for the air supply. Gotta make sure it is clean, dry air if used.
Click to expand...

Vortex coolers use a lot of air if they run a lot. Often if you put the heatsink outside, and run the vortex cooler on a thermostat, the cooler does not run all that much.

There are also liquid heat exchangers that can be added if you have cooling water available.
 
I should have picked up on this thread earlier. There are thousands of VFDS underground in mines completely type 4 enclosed, you do a dirty air system ? gasket heat sink in a filtered forced air duct. Thousands of VFDS in mill and commodity plants packaged the same, thousands of VFDS on oil wells taking care of all the rich Arabs oil wells in well over 50C ambient temperatures, I could go on. The integrators got past this long ago and have matured against their life long enemy, thermal degradation.

This thread began with what would be a VSI, PWM inverter. Pretty much the only type out there any more under 1000HP.

All have IGBTS sitting atop an aluminium heat sink. They can all run that heat sink up to 80+C. If you sink that heat out of your system with the right packaging, you only have a third of your heat load to contend with.

So do the math. They are all 97-98% efficient, lets round off 150HP to 100kW (unless you are from outside the US, you started with kW anyway). So we have 3kW or envision 30 x 100Watt lights bulbs of heat left.

Now put a stirring fan to create some turbulence in the type 4 section where the 1kW remains so as to prevent hot spots and distribute your remaining heat evenly to the exposed areas of your enclosure material, cold rolled steel for example. (no fibreglass please) Now figure out the thermal transfer per total exposed area and size your final enclosure. If your space is limited, consider a different material or add a heat exchanger, little ac unit, what have you.

But always remember - don't ever let any one extol the virtues of their brand over another. It is how they are packaged, Japanese, German, American or otherwise. All the VSI PWM varieties have the same limitations, anyone want to guess at how many IGBT factories are out there and whether amp for amp one IGBT will die sooner than another?

The really good VFD people should also be able to de-rate component MTBF also, ? if they can?t they are salespeople ??so beware.

I have to read back up this thread ? anyone mentioned F sub C yet?
 
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