[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]

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]

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]

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.

[in2steam]

Instead of building it just buy it, these work excellent for a router or sander...

clearvuecyclones.com

Although I don't know what the shipping would be to the sunny side would be. They were $165usd for one thats designed to run on about a 6.5hp vacuum with around 4" hose. These guys went through the trouble of getting the design down. They recomend changeing the vacuum to a HEPA filter.
When I said a 75 HP engine I was figuring a typical smallish diesel in a truck, w/turbo will run at the very least 1000 cfm(check your math). A hyped up carb v-8 will use anywhere between 650-850 cfm off idle depending on the carb and compression.

I still cannot believe that that type of system would work with smaller then wood shaving sized particles. Its all about speed when you use a cyclone and I don't think you can get it, granted the purpose here is to cool and not clean.

chris

[Warpspeed]

Instead of building it just buy it, these work excellent for a router or sander...

clearvuecyclones.com

Excellent advice, I was not aware that these could be bought off the shelf in smaller sizes.

When I said a 75 HP engine I was figuring a typical smallish diesel in a truck, w/turbo will run at the very least 1000 cfm(check your math). A hyped up carb v-8 will use anywhere between 650-850 cfm off idle depending on the carb and compression.

You must be joking! The normal accepted figure is 1.5 CFM per horsepower for most internal combustion engines at full power.

Sure, a hyped up V8 may use 650 to 850 CFM flat out if the expected power is in the 433 to 567 Hp range, (which is not unrealistic). But certainly not just off idle.

And you are seriously suggesting that a very small 75Hp truck motor consumes even more air than a souped up V8? I think it is you that need to check your maths.

I still cannot believe that that type of system would work with smaller then wood shaving sized particles. Its all about speed when you use a cyclone and I don't think you can get it, granted the purpose here is to cool and not clean.

chris

No it is density. Air is light, even microscopic dust particles are actually solid material, and relatively heavy.

Well, vacuum cleaners and truck air cleners trap extremely fine dust very effectively, otherwise they would be completely useless. A vehicle air filter that will not stop anything smaller than a wood shaving would be a complete waste of time. The purpose of the air filter is to CLEAN the air, not cool it????

[in2steam]

Must of the crap cloggs are filters, the the cyclone does get rid of the bigger particles, they open to the air so its hard to say, but the filters are normally clogged by 10-15k miles(20-30k kiloM) in the summer and about 30 in the winter, we run most of those truck 24-7 around 250k a year.

I am going to hook up my flow meter if I can find it to a cat 3126b at work this weekend, granted these are about 175-205 HP, free air on a diesel is entirely different then on a gas engine were they run a vacuum(I truthfully thought that cfm rating on a carb was about what they draw), I will except that you only get 1.5 CFM on a gas engine i have never equated it that way, diesel with a turbo thats enitrely different story.
I honestly don't know what the boost runs at on the cats, I know if the guage is accurate our 6.0L ford turb DI runs about 15lbs of boost the cats are about the same size, but the cats have big truck filters the ford does not. At ilde they don't draw alot of air, but at speed they draw incredible amounts of air. The meter is a little small but it should work, its got a read out to 900 CFM.

whats the conversion rate for L to cu anybody off the top of there head?
231 is to a gallon I think...

chris

[Warpspeed]

Chris, one liter equals 61.02 cubic inches.

Engine airflow can be estimated in two ways. The first is engine capacity, multiplied by rpm, multiplied by volumetric efficiency. As an engine is just a piston air pump, that works out fairly well for normally aspirated engines. Just remember to use half the actual rated capacity for four stroke engines.

Turbocharging complicates things, and I am in a discussion right now at an engine tuning Forum that drifted onto this very subject. The basic rule for sizing a turbo is still 1.5 CFM of air per required horsepower.

http://efi101.com/forum/viewtopic.php?p=18093#18093

If your turbocharged CAT diesel is in the 200Hp range, then expect the airflow at rated maximum power rpm to be fairly close to 300 CFM. We shall see..

What type of airflow meter do you have Chris ? I use one of those propeller type anemometers used in the airconditioning industry. For more accurate airflow measurement on my home airflow bench, I use orifice plates and a water manometer. Here are some pictures of my airflow bench that I posted over at the flowbench Forum. I post there as "Tony".

http://www.tractorsport.com/cgi-bin/...ct=ST;f=9;t=35

[in2steam]

yes my meter was..... a blade flow sensor....

They don't like getting screwdrivers through the blades whilst running at high rpm. It read 440 at the last reading that was coming off of idle(maybe 900 rpm) without a load, the turbos don't really load out untill 1k and then only with a load, I had it rigged and was going to close the hood backup, I had it taped to the intake and block the other(there are two) and had a screw driver in my hand. The hood cowl is spring loaded and well the screwdriver could not have aimed better..... At least that one was free....

I did upon recommendation of one of the mechanics we employ hook up a computer and see if it had a cfm reading. It did not, at least not that I could find, but the computer interface for that system is lack luster compared to OBD II of cars and light trucks. We got a brand spanking new ford 650 with cummins in it this week I might play with that one and see...

It read 300-350 at idle, those engines surge at idle a little bit and my tape job was not the best. I don't know the exact HP of that engine, they can be changed depending upon the size of the radiator, I think that one was only 175 as it is the oldest and least modified. We have one set at 210, and another set 225 or so I am told, its all done in the computer at the dealer.

chris

[millminer]

protecting a VFD from contamination

(1) Sealed cabinet.
(2) Rear of cabinet heavy duty finned material.
(3) Fan cools heatsink from outside, cabinet cool!.
(4) End of clogged filter problem. :-)

[Warpspeed]

How was your air velocity meter connected? and what units were you actually reading in?

An air velocity meter cannot be just taped over an air intake to directly read in flow!

Unless your round intake air pipe is roughly 13.5 inches in diameter, (or close to one square foot in flow area). Then the air velocity reading in feet per minute will be about the same as cubic feet per minute flow.

But just taping a velocity meter directly over the air intake of your engine tells you nothing directly, without a fair bit of subsequent calculation.

How much air is flowing through a 2.75 inch pipe if the measured velocity is 32.8 knots ?

How much air is flowing through a 4.13 inch pipe if the measured air velocity is 300 feet per minute ?

Just because an air SPEED number displayed is 300 in some particular units, that is highly unlikely to correspond directly 300 CFM VOLUME flow.

Sorry to hear about your mishap. Yesterday I dropped my multimeter onto concrete with a similar result. Time to buy another one....

[in2steam]

Thats ok my primary car got impailed by buick today while I was in the basement hooking up my lathe, so the only playing with my new ford at the part time job will be towing my car to the car crusher. Then I blow the main circuit in my house, its a bad idea to use your VOM in amps(I will take my lumps for that now) connection across the line, at that point I stormed upstairs and opened a beer I had enough-I don't drink. I have not even done a tally what got screwed up then, but meter is no longer the same along with one battery chargerer and a cheap radio. I am ready to write this week off at least its a holiday week here so its short.....

To answer your questions, the meter is/ was set into a 15" piece of rubber pipe/hose like those used in a PVC/GI drain vent here in the states, its flexible. The intakes(one on top other on bottom) of the truck is on the order of 13" I cannot say i measured the size though it was slightly less then my tube I stuffed some cardboard and tape between the two. It reads in MPH so like you said its close to one cub, but not dead nuts on. The meter does not like spikes so the high of 350 was more then likely less. I had enough cord for the meter to tape the meter to the windshield and take it for a spin, I wanted to get a nice even long drawn reading.
This is/was developed to measure the cfm of a larger blower unit at work(full time) of the same diameter, its not incredibly accurate but I would say its with in 10' or less. It was used held in the center of the piece with a couple dowels about 7-8 inches inside, it reads in velocity of feet per minute. I think i got it from MSC or mcmaster-carr for around $300 with the tube although I don't recollect at this time as it was a number of years ago. I had to bend it(the rubber) slighlty to get the hood cowl down had I not had my screw driver in my hand things would have gone well as the hood got the best of me. My boss also pointed out to me today as I called to borrow a truck for my car that I put a rather large crack in the cowl from my reaction of pulling the screw driver out fast.....

edit:btw the number display I factored by 10, so I saw only 35(mph) oddlly untill I taped the top half of the intake off I got only 10(mph). I wrote that on the side of tube so years ago when I did that my assumption is that I figured it to be close.
chris