protecting a VFD from contamination

[bilinghm]

My shop is pretty dusty. I worry that my wide open Hitachi VFD will fill up with junk and short out. I mounted it high on the wall (above 7 feet) but I wonder if anyone has a good solution that won't impact proper cooling. How about mounting an air conditioner filter above the unit to catch dust? Suggestions?

Bill

[in2steam]

Bill I work in the printing industry, we have enclosed every one of our drives that were not already done so. Very simply get you average run of the mill cabinet, enclose it, add at least one fan(best to be pushing into the box), and but some filter mat. The cost of the box is no even close to replacing the box, plus it helps as a heat sink. Every drive I have worked with will have specfic instructions about clearances inside an enclosure, drives can handle fairly hot areas, hotter then most people can tolerate, but as with anything electronic the cooler that you keep it the longer it will last. I jsut finished an enclosure for a 5 hp mitsbushi drive and plc the enclousre was around $40 the fan was about $15, the filter mat I have in roll form I use from grainger 4wz60 i think but you would not need that much as its in the 100' length but a similiar material should work, its slightly sticky so it grabs dust out of the air. Also the when changing the filters( I put one on the outlet also) I blow out the cabinets with a brief indirect blast of air.

chris

[JRaef]

Fans and filters are one way to go, as long as you are fastidious about cleaning the filter media. If not, the filter clogs quickly, the air movement stops, the VFD fries.

For small VFDs however, a quick and dirty rule of thumb if to take the volume of the VFD case itself and multiply it by 6 to get the volume of a sealed (unventilated) box such as NEMA 12 or NEMA 4 as long as the ambient is 10 deg. C below the VFD max. temperature rating. In other words, if your VFD is rated for 40 deg. C (104 F) as most are, as long as your ambient is below 30 C (86 F) you can seal it up into a larger box. So if your VFD is 4 x 5 x 3, that is 60 cu. in.; X 6 = 360 cu. in. for a NEMA 12/4 box. Since you probably don't want a box over 6" deep, 360/6 = 60 sq. in. which is 10 x 6. So you can put that VFD into a 10 x 6 x 6 sealed box and it will be OK dissipating it's waste heat by radiation through the sheet metal in a shop environment.

BTW, don't use this rule outdoors because radiant heat from the sun makes a big difference.

[bilinghm]

Thanks for the excellent advice. I am currently considering a box built from heavy wire mesh and covered with filter matting (universal, cut-to-size air conditioner filter material). The idea would be to mostly rely on convection cooling (I have my VFD programed to only run the fan when temperature requires). With this open structure, I seems that it would not impede cooling but provide pretty good protection from dust.

[Warpspeed]

Better still run some fresh clean outside air first into a fan, then through some ducting to your VFD enclosure. If everything is pressurized, nothing can get in. Any small leaks will leak air out, not suck dust in. Then vent the hot air out of the VFD enclosure through a dust filter on the bottom.

[JerryFlyGuy]

This is 'in effect' what I've been working towards on my machine. I've made a control console which houses the PC, my VFD , my drives as well as my G100 and power supply. I made a small air box on the side of the machine. I'm using a small airfilter from Walmart [out of the automotive section] as a filter. However I'm pulling air through this filter and pressurizing my cabinet w/ it, there are several openings in various locations where the heat can escape, yet having the cabinet pressurized should keep all the dust out of the cabinet. I'll let you know how it works here in the next few weeks.

[in2steam]

Originally Posted by Warpspeed Better still run some fresh clean outside air first into a fan, then through some ducting to your VFD enclosure. If everything is pressurized, nothing can get in. Any small leaks will leak air out, not suck dust in. Then vent the hot air out of the VFD enclosure through a dust filter on the bottom.

In a dusty work area this is most certainly better, but the outside air is not always clean, esp in my area in this time of the year, between pollen, ragweed, and dogwood, and dandy lions the heatsink would clogged with in a week, not to mention the normal air dust. Even in a my "clean rooms" I have to replace the filters from dust at least bi monthly. The ones that filter outside air are monthly and they are not anything to write home about, I live in a northern climate in the us, 6 months out of the year I could go and look and the filters would be clean. The other 6 they would be clogged every month, so moral of the story is that its not always any cleaner outside. I would always use a filter with inside or outside air going through any fan.

chris

[Warpspeed]

If filter clogging is that bad, I would put a centrifugal "cyclone" type dust extractor ahead of any filter medium. Large diesel trucks almost all use these, very efficient drum type dust extractors, and your nearby truck dismantling graveyard should have a suitable selection available.

A centrifugal pressure blower, and some PVC pipework could then carry your clean air supply to wherever it needs to go.

[in2steam]

Originally Posted by Warpspeed If filter clogging is that bad, I would put a centrifugal "cyclone" type dust extractor ahead of any filter medium. Large diesel trucks almost all use these, very efficient drum type dust extractors, and your nearby truck dismantling graveyard should have a suitable selection available. A centrifugal pressure blower, and some PVC pipework could then carry your clean air supply to wherever it needs to go.

A worthy comment how ever I am talking about low psi high volume, these would not work with these(listed in my last post), these are for instance oven intakes, air handlers and HVAC units. Even for a VFD with a small housing you should only need minimal investment in filter mat, around $2.00(although you will end up buying more the first time) a year and a small 4-6" fan. The system you are talking about at bare minuim would cost several hunderd dollars and you would need around 3 HP(if not more) to make it work correctly, these systems work excellent at cleaning dirty air at the source like a saw or router not at cleaning air in general. Those systems use filters to post scrub the air, wereas a good venting system for cooling in a housing prefitlers the air and post filters the air and keeps a constant low psi in the housing.
Chris

[Warpspeed]

Have you ever checked out how a Dyson vacuum cleaner works? They use a patented multi stage cyclonic dust extraction system instead of the usual canvas "bag" type filter used in most other domestic vacuum cleaners.

A domestic vacuum cleaner is not a very high flow device, but probably roughly sized about right for what you might need to cool a single fairly average sized VFD.

Cyclonic air filter systems can be made quite small or absolutely gigantic.

The advantage of a centrifugal cyclonic dust extractor is that it can continue to remove vast amounts of dust and very small particles without blockage or air restriction. Any porous filter medium, by it's very nature stops dust by entrapment and blockage.

The interstate truckies, serious off road 4WD guys, and lunatic desert racers all use the cyclonic drum type air cleaners, because they can remove LITERALLY a bucket load of dust, without restricting airflow.

The solid debris just falls into the bottom to be collected and removed.

There is no real practical limit to how much dust it would take to become full. You could couple up a 55 gallon drum dust collector bin onto the end of a really small low flow "Dyson sized" cyclonic filter.

[in2steam]

Originally Posted by Warpspeed Have you ever checked out how a Dyson vacuum cleaner works? They use a patented multi stage cyclonic dust extraction system instead of the usual canvas "bag" type filter used in most other domestic vacuum cleaners. A domestic vacuum cleaner is not a very high flow device, but probably roughly sized about right for what you might need to cool a single fairly average sized VFD. Cyclonic air filter systems can be made quite small or absolutely gigantic. The advantage of a centrifugal cyclonic dust extractor is that it can continue to remove vast amounts of dust and very small particles without blockage or air restriction. Any porous filter medium, by it's very nature stops dust by entrapment and blockage. The interstate truckies, serious off road 4WD guys, and lunatic desert racers all use the cyclonic drum type air cleaners, because they can remove LITERALLY a bucket load of dust, without restricting airflow. The solid debris just falls into the bottom to be collected and removed. There is no real practical limit to how much dust it would take to become full. You could couple up a 55 gallon drum dust collector bin onto the end of a really small low flow "Dyson sized" cyclonic filter.

Again cyclones are high flow high psi deivces when used as a seperator, they work best in a removal of dust, not in cooling air as they add heat.

Vacuum cleaners are high psi and med to high flow, and they generate heat.
For instance the one dyson I looked at was 12 amps, thats not real practical consdiering a small cooling fan will draw around .2 amps.
And even the dysons have filters, just like any centriufugal system that cleans. The other problem is that you would be moving way to much air around, cooling is almost always the most effective at slower speeds then faster when transfering heat. Vacuums are almost always universal motors, which means they have brushes, sooner or later( more likely sooner) they will wear out and stop working.

An engine bare min. is around 75HP, these would be high flow, low to med psi. I drive a truck part time, the filters are good, but they are also fairly expensive and sooner or later clog. The dust that they don't catch is sign that the engine itself cannot generate enough static psi in the housing to work proper like a comercial seperator.

I suggest you read bill pentzs web site at billpentz.com , again its a noble idea and your right it would take gobs of stuff out of the air, and may actually have a use in some sort of really big application in a really dusty area were no cleaner air can be had. But we are talking about cooling a smallish VFD in a cabinet, it does not make sense to cool the VFD down with a vacuum cleaner motor that rates out higher then the VFD. In this case it would still be best to use a small .1 HP motor/fan and some filter mat.

chris

[Warpspeed]

I agree with you Chris, vacuum cleaner motors are noisy, hot running, inefficient, fast wearing machines, with a short life. Totally unsuitable for cooling anything.

The vacuum cleaner motor may be rubbish, but the cyclone filter is probably about the ideal size to filter the cooling air to a small VFD.

Cyclone filters offer very low forward pressure drop, if it were otherwise, they just would not be suitable to use on any internal combustion engine.

Realize too, that a 75Hp small truck engine will only consume around roughly 112 CFM of air absolutely flat out. And funnily enough 112 CFM is also about the typical rated unrestricted flow for a good quality four inch computer cooling fan! A small truck cyclone would not be much larger than a vacuum cleaner cyclone anyway. It is really just steel versus plastic. The construction is pretty much the same. I suppose it depends on which is easiest to find.

I still feel that a small cyclone, followed by a conventional porous filter, hooked up to a quiet low rpm fractional horsepower centrifugal blower, would be ideal.

Here are two really awful photographs I have just now hurriedly taken of a Dyson vacuum cleaner cyclone I have here. This shows the relative size and simplicity.

I intend to copy this in steel sheet, scaled up slightly to make my own high power permanently installed shop vac system for my home mechanical workshop.